TREATISE FORTIFICATION %td\mB bclibtrcb t0 dBffiars reatring far lljc BM. CAPTAIN LENDY, F.G.S., F.L.8., t mRF.OTOR OF THE rilAnTirAI. MILITARY C:OI,I,KOE OF SUNBHIIV. •• Tho use of the spade, pick-axc, and barrow is as essential for the dcfeusive, as that of the nuiske I bayonet is for the olfcnsivc operations of tlic anny." — Article 56, Duties in Camp — Queen's Regulations. LONDOOS^ PUINTKI) AND PUBLISHED BY W. MITCHELL, MILITARY BOOKSELLER, 39, CIIAUING CROSS. % [entered at stationers' hall.] DEDICATED (by permission) TO H.E.H. THE DUKE OF CAMBRIDGE, ETC. ETC., COMMANDER IN CHIEF. [UFI7BRSITT1 PEEFACE For a reason difficult to understand, candidates for the Army are not expected to possess any information on tliis important branch of their future profession. A trifling knowledge of Fortification was demanded of them a few years ago ; but, strange to say, one of the first so-called improvements introduced into army education, after the Crimean war, was the entire suppression of this subject. However, the competition for entrance into the Staff College, and the qualifications required of candidates for Staff appointments, have kept up the study of the science among a certain number of officers of the Line. A small sketch of Fortification was pubhshed by me a few weeks before the alteration in the subjects of examination was made, but as it was intended merely to give a general, and therefore superficial, knowledge to young officers, it became necessary to prepare a series of lectures for those who were reading for the Staff. Having, more especially, the examinations in view, it was essential to avoid speculations and theories not founded on facts, and to compile from such sources only as would be likely to prove practically useful. This I have attempted to do, borrowing from the following sources : — vi PREFACE. The Courses in use at Woolwich, Sandliurst, and Chatham ; the Professional Papers, the Aide-memoire to Military Sciences; the Memorial du Genie ; the Aide-memoire d'Artillerie ; the excellent works of Zastrow, Baron Maurice, Noizet, Mangin, Choumara, Dufour, Mandar, Jebb, Emy, &c. &c. To adhere to the elements of the subject, and yet to convey a lai-ge amount of instruction in a small compass, has been my endeavour. Three-fourths of the English Staff have read Fortification vrith me. This course was compiled for them, it is now printed at their urgent request, and is intended for them and their successors. A. F. LENDY. Sxmburi/, September, 1861. DIVISION OF THE WORK CHAPTER I. ARTILLERY. PAGE. Section I. — Various Kinds of Ordnance 1 Definitions. Reinforce. Chase. JIuzzle. Bore. Calibre. Axis. Dispart. Breech. Chamber. Trunnions. Windage. Prepoiulcrance. Guns. Shell Guns. Carronades. Howitzers. Mortars. Section IT.— Organization of Artillery 5 Field Artillery. Horse Ai-tillery. Artillery of Position. Mountain Batteries. Section HI.— Artillery Carriages 6 Field Gun Carriage. Limber. Ammunition Wagon. Siege Carriage. Ho- witzer Carriage. Garrison Carriage. Common Platform. Dwarf Traversing Platform. Carriages for Transport. Naval Carriages. Mortar Beds. Ar- tillery Horses. Section IV. — Projectiles 10 Solid Shot. Hollow Shot. Grape Shot. Canister. Common Shell. Jlnrtar Shell. Shrapnel and Diaphragm Shells. Carcasses. Light Balls. Smoke Balls. Hand Grenades. Signal Rockets. Congreve Rockets. Rocket Tube. Service Charge. Cartridge. Wads. Tubes. Portfires. Quick- match. Shell Fuze. Time, Concussion, and Percussion Fuzes. Table of English Ordnance. Section V. — Rifled Ordnance 18 Cavalli and Wahrendorff Rifled Gnns. Louis Napoleon. Armstrong Gun. Shell. Armstrong Carriage. Range. Whitworth Gun. Small Arms in Service. Successive Improvements. Enfield Rifle, &c. Section VI. — Gunnery 23 Pointblank. Line of Metal. Elevation. Tangent Scale. Line of Sight. Trajectory. Ranges of Ordnance. Penetration of Projectiles. Direct, Oblique, Slanting, Enfilade, Reverse, Pitching, Plimging, Grazing, Flanking, Vertical, and Ricochet Fires. CHAPTER H. PRINCIPLES OF FORTIFICATION. Definitions : Natural, Artificial, Permanent, and Field Fortification. . . 30 Section I.— Covering Mass and Ditcu 31 I'arapet. Thickness of Parapet. Measure of Slopes. Superior, Interior, and Exterior Slopes. Banquette. Slope of Banquette. Line of Fire. Interior and Extei-ior Crests. Rampart. Ditch. Escarp. Counterscarp. Berm. Depth. Width. Glacis. Covered Way. Command. Relief Breast-work. viii DIVISION OF THE WORK. PAGE. Section II.— Outline 37 Properties of Salient Angles. Undefended Angle. Capital. Line of Defence. Ke-entering Angles. Dead Angle. Dimensions of Faces. Fundamental Principles. CHAPTER III. DRAWING OP FORTIFICATION. Section I. — Scales 42 Ordinary Scales. Diagonal Scales, llarquois Scales. Protractor. Section II. — Projections 52 Plan, Elevation, Section, Profile, &c. Section III.— Isometeical Projection 65 CHAPTER IV. FIELD WORKS. Section I. — Open Works 75 Redan. Lunette. Tenaille. Double Redan. Tenaille Head. Queue d'Hi- ronde. Bonnet de Pretre. Hornwork. Crownwork. Section II. — Enclosed Works 77 Redoubts. Star Forts. Tracing of Star Forts. Forts. Bastions. Curtain. Flank. Face. Gorge. Demigorge. Flanked Angle. Angle of Defence. Angle of Curtain. Shoulder Angle. Diminished Angle. Ditches of Bas- tioned Fronts. Demi-Bastioned Fort. Blockhouses. Section III.— Continued Lines 87 Properties of Continued Lines. Various Sorts of Contiiraed Lines. Lino of Front. Zone of Defence. Tenaille Lines. Lines of Vaubau. Indented Lines. Bastioned Lines. Section IV. — Lines with Intervals 93 Their Properties. Tracing of a Line of Lunettes. Reduits. CHAPTER V. SELECTION OF AN OUTLINE. Causes which Influence the Selection of an Outline. Ground and Object in View. Places du Moment. Garrison of Open Works. Garrison of En- closed Works. Maxima and Minima of Enclosed Works. Calculation of the Maximum and Minimum of a Bastioned Front 98 CHAPTER VI. ACCESSORY DEFENCES. Section I.— Autilleuy 106 Barbettes. Their Construction. Ramps. Embrasures. Neck. Mouth. Sole. Cheeks. Genouillero. Tracing of Embrasures. Merlon. Hurtcr. Common Platform for Guns and Mortars. Alderson Platform. Madras Platforms. Tracing of Convergent and Divergent Embrasures. DIVISION OF THE WORK. ix PAGE. Section IT.— Defence OF THE DiTfii ......... 115 Caponiers. Galleries of Counterscarp. Stockades. Retirade. Section ni.— Obstacles 119 Palisades. Praises. Stockades. Tambours. Abattis. Entanglement. Che- vaux-de-Frise. Pickets. Crows' Feet. Trous de Loup. KiHe Pits. Fougasse. Shell Fougasse. Stone Fougasse. Inundation. Dam. Time necessary to form an Inundation. CHAPTER VII. DETERMINATION OF THE PROFILE OF FIELD WORKS. Section I.— Defilade 127 Plane of Site. Plane of Defilade. Defilade of an Open Work. Defilade of an Enclosed Work. Parados. Traverse. Bonnet. Section II. — Calculation of the Deblais and Remblais 131 Calcidation for a Work not Defiladed. Ditto for a Work Defiladed. Defects of the Method. Centrobarique Method. Method of the Prisms. Simplifica- tion of the Centrobarique Process. Ditches with Variable Profile. CHAPTER Vni. EXECUTION OF FIELD WORKS. Section I.— Constrcction 140 Tracing on the Ground of Open and Enclosed Works. Defilading by the Plane of Site. Defilading by the Plane of Defilade. Defilading by sinking the Terreplein. Defilading of Enclosed Works. Profiling. Tracing of the Ditch. Division of Labour. Time Required. Section H. — Revetments 148 Fascines, small and large, Gabions. Iron Gabions. Sods. Sandbags. Hurdles. Planks. Section IH.— Communications 152 Closing of the Gorge. Passage. Traverses. Construction of Traverses. Barriers. Field Bride CHAPTER IX. MILITARY POSTS. Trenches. Defence of Hedges and Roads (from Colonel Jebb). Houses : their Site, Dimension, Distribution, Construction, Dependencies, and Ap- proaches. Of the means to prepare for Defence in the Interior and on the Outside. Farms. Churches, Castles. Mills. Woods. Defiles. Organization of the Defence of a Village CHAPTER X. ATTACK AND DEFENCE OF FIELD WORKS. Attack by Open Force. Attack by Surprise. Destruction of Obstacles. Defence X DIVISION OF THE WORK. CHAPTER XI. MILITARY BRIDGES. Military Bridges. Pontoons. Blanshard Large Pontoons. Saddles. Balks. Chesses. Raft. Construction of the Bridge. Small Pontoons. Francis and Fowke's Pontoons. Boat Bridge. Cask Bridge. Raft and Float Bridges. Trestle and Pile Bridges. Rope Bridges. Varieties of Small Bridges. Flying Bridge. Trail. Ferry. Passage of Rivers. Fords. Ice. Weight of Troops and Superstructure. Buoyancy. Buoyancy of Casks. Strength of Timber and Material. Strength of Cordages. Tetes-de-Pont. Booms CHAPTER XH. VAUBAN'S FIRST SYSTEM. Polygon. Front. Regular and Irregular Fortifications. System. Tracing of Vauban's First System. Enceinte. Tenaille. Main Ditch. Ravelin. Caponier. Covered Way. Salient and Re-entering Places of Arms. Tra- verses. Crochets. Outworks. Advanced Works. Detached Works. Profiles of the System. Empty, Full, Flat Bastions. Ramps. Pas-de- souris. Sally-ports. Batardeaux. Counterforts CHAPTER XHI. ATTACK OF A FORTRESS. Section I. — Irregul.\r Attacks Sm-prise. Escalade. Scaling Ladders. Artillery Attack. Bombardment. Blockade. Siege Section II.— Siege a. — Preliminary Operations. Investment. Reconnoissance. General Plan. Selection of the Pomt of Attack. Implements. Prolongation of the Faces and Capitals. 6.— First Parallel. Opening of the Trenches. Profile of Trenches. Batteries. Ricochet Batteries. Counter-Batteries. Cavalier, Elevated, Sunken and Half Sunken Batteries. Epaubnent. Traverses. Expence and Laboratory Magazines. Approaches, c— Second Parallel. Its Profile. Flying Sap. Demi-Parallels. Regular Sap. Standing Sap. Double Sap. Mantlets. Serpeutme Sap. Double Dh-ect Sap. Blinded Saps. f/.— Third Parallel. Crowning of the Covered Way. Circular Portions. Trench Cavaliers. Breaching Batteries. Breaching. ('.— Descent into the Ditch. Gallery. Blind Frames. Passage of a Dry and ' Wet Ditch. Assault, l.tidgiiicnt. DIVISION OF THE WOHK. si CHAPTER XIV. DEFENCE OF A FORTRESS. PAGE. Preparations before the Investment. Periods of Defence corresponding to the Periods of Attack. Lines of Counter-approach. Fleches. Retrenchments. Blindages. Blinded Batteries. Defence of the Breach. Journal of Siege . 248 CHAPTER XV. FORCES EMPLOYED IN A SIEGE. Armament and Ammunition for the Defence. Strength of the Garrison. Stores. Force of the Besieging Army. Battering Train. Quantity of Ammunition 255 CHAPTER XVI. MILITARY MINING. Section I. — Mines 262 Shafts. Galleries. Branches. Framing. Frame. Sinking a Shaft. Excava- tion of a Gallery. Inclined Galleries. Branches. False Frames. Casing. Sinking a Shaft. Construction of Galleries. Ventilation. Miner's Tools. Trucks. Chamber. Tamping. Conjunct Mines. Focus of Ignition. Focus of Explosion. Crater. Radii of Rupture. Radius of Crater. Radius of Explosion. Line of Least Resistance. Common Mines. Undercharged and Overcharged Mines. Charge of Powder. Globes of Compression. Camou- flets. Blasts. Section II.— Coi'ntek-Mines 278 System of Envelope Galleries. System of Gumpertz and Lebrun. System of Dufour. Gallery of Counterscarp. Magistral Gallery. Envelope Galleries. Galleries of Communication. Listening Galleries. Escarp Galleries. Dis- position of the Mines. Subterranean Warfare. Attack by the Mine. Gillot's Method. Breaching. Destruction of Revetments, AYalls, Galleries, Bridges, &c. CHAPTER XVH. THE SYSTEMS OF VAUBAN. Discussion of the First System. Tracing of the Second System. Tracing of the Third. Profiles of the Third. Properties of these Systems. Their Attack. System -nith Orillon 289 CHAPTER XVIII. MODERN SYSTEM. Tracing of the Modern System. Profiles. System of Cormontaingne. Tracing and I'nililf. Attack of the Mudeni System 304 xii DIVISION OF THE AVORK. CHAPTER XIX. SYSTEMS OF CCEHORN. PAGE. Tracing of the First System. Profiles. Details of a Front. Properties of the System. Outline of the Second and Third Systems. Attack of the Fu-st System 315 CHAPTER XX. PERMANENT BASTIONED FRONTS. Section I.— Tracing of Fortresses 332 Regular and Irregular Places. Principles of Fabre and Cormontaingne. Shape of the Town. Rivers. Section II. — Tracing op a Front 334 Exterior and Interior Polygons. Relief. Curtain. Flanks. Faces. Flanked and Duninished Angles. Tracmg on Conditions. Section III.— Interior Works 337 Cavaliers. Curtain Cavaliers. Interior Retrenchments. Casemated Retrench- ments. Section IV.— Escarps 342 Fausse-braye. Cherain-des-Roudes. Solid Revetments. FuU, Demi, Leaning, Rectangular, Counter-sloping, Sloping. Revetments of Vauban and Cormon- taingne. Counterforts of Vauban and Modern Engineers. Counter-arclied Revetment. Independent Scarp Wall. Foundations. Section V.— Ditch .350 AVidth and Depth. Cunette. CHAPTER XXI. ADDITIONAL WORKS. Section I.— Outivorks 352 Ravelms. Reduit. Coupures. TenaUle. Couuterguards. Front of Counter- guards. Envelope. Tenaillons. Demi-Teuaillons. Horn-works. Crown- works. Covered Way. Reduits of Places of Arms. Section II.— Advanced AVorks 361 Lunettes. Lunette d'Ar^on. Improvement of Maurice. Fleclies. Horn- works. Crown-works. Advanced Ditch. Advanced Covered AVay. Section III.— Detached Works 3G6 Various Forms of Detached Works. Loopholed Scarp AA^all. Machicoulis. Galleries of Reverse. Bastionets. Detached Lunettes of Gosport. Their Reduits. Citadels. Intrenched Camp. Section IV.— Coast-batteries . . . . ■ 374 Construction and Armament of Coast-batteries. Martello Towers. Toui-s- Modele of Napoleon. Batteries of Bomarsund. Battery of Shoreham. DIVISION OF THE WORK. xili CHAPTER XXII. DETAILS OF PERMANENT WORKS. PAGE. Section I.— Defilade 382 Defilade of Permanent Works. Fortifications in Mountainous Districts. To find the Command from Conditions. Section II.— Communications 385 Posterns. Pas de Souris. Ramps. Caponiers. Sally-ports. Gateways. Drawbridges. Old Pattern. Bascule. Dobenheim's. Belidor's. Roller- Bridge. Poncelet's Bridge. Section III.— Loopholes 394 Construction of Loopholes in Masonry. Embrasures. Revolving Loophole. Machicoulis. Section IV.— Casemates 400 Ordinary Casemate. Haxo's Casemates. Their present Construction. Powder Magazines. Section V.— Water 405 Influence of Water on the Profile. Inundations. Sluices. Flood-gates. Barrage. Batardeaux. Waste Weirs. Section VI.— Details 411 Execution. Deblais and Remblais. Estimates. Military Zone. Scale of Comparison of Cormontaingne. Moments of Fourcroy. CHAPTER XXIII. PRINCIPAL BASTIONED SYSTEMS. Outline of Bousmard's System. Outline of Chasseloup-Laubat's System. Outline of Noizet's System. Tracing of Dufour's System. Principles of Choumara. Outline of Haxo's System 413 CHAPTER XXIV. MONTALEMBERT AND CARNOT. Section I. — Montalembeut 437 Perpendicular Fortification. Tracing and Profiles. Discussion on its Properties. Polygonal Fortification. Tracing and Profiles. Circular Fortification. Towers of Montalembert. Section II.— Carnot 449 Principles of Carnot's Defence. Tracing and Profiles of his Bastioned System. Appreciation. Outline of the Second and Third Systems of Carnot. CHAPTER XXV. GERMAN FORTIFICATION. Section I.— German Systems 457 Tracing of Fort Alexander. Profiles. Front of Gemersheim. Front of Ingoldstadt. Discussion of their Properties. Prussian System and Profiles. xiv DIVISION OF THK WORK. SEcrroN 11.— German Fortresses . . . . 4f>8 Verona's Bastion. Forts of Cologne. Fortification of Radstadt. Ulra. Mayence. Maximilian Towers. Towers of Verona. CHAPTER XXVI. DEFENCE OF FRONTIERS. System of Vauban. System of General Rogniat. System of General Duvivier. Fortification of Capitals. Defect of Systems. Maritime Frontiers. Influence of Rifled Weapons on Fortification 481 CHAPTER XXVn. HISTORY OF FORTIFICATION. Antiquity of Permanent and Field Fortifications. Invention of Ai-tillery. . 488 Section I.— Italian School 490 Italian System. Spanish System. San Jlicheli. Tartaglia. Carpi. Urbin. Castriotto. JIaggi. ISIarchi. Bnsca. Floriani. Rosetti. Section II. — German School 495 Albert Durer. Speckle. Dillich. Rimpler. Gricndel. Werthmuller. Suttinger. Landsberg. Voigt. D'Harsch. Sturm. Herlin. Glasser. Herbort. Augustus II. Pirscher. Virgin. Section in.— Dutch School Freytag. Marolais. Russenstein. ' Scheiter. Coehoni. Section IV. — French School 514 Errard. Deville. Pagan. Vauban. Mallet. Blondel. Bernard. St.Remy. Rosard. Cormontaingne. Belidor. Rottberg. Robillard. Marshall of Saxe. Filey. La Chiche. Falois. Rhana. Montalembert. Cugnot. Trincano. Reveroui. Bousraard. Chasseloup. Camot. Noizet. Dufour. Choumara. Haxo. General Index 531 ERKATA. PAOK. 2. line 14, {nskad nfgomer read Gomer. ;■), „ 8, „ ■ Millar „ Millar. 11, „ 1, „ HollwB Shot read (20). Hollmo Shot. n, ., 5, „ (1) „ (21). 2(), „ 9, „ A sufficient „ (45). A sufficient. 28, „ 7 from bottom, instead of 1797 read 1097. 45, ., 12, instead of nto ten ,, into ton. 45, „ 16, „ ?49 2_40 ' " " .W " 50 47, .. 4, „ The diagonal lines being read The diai,'onal lines. l)ein£;. 52. .. 5. .. find a means read find means. 5r., ., 5, „ GG „ GG'. 56, „ 11, „ GG „ GG-. 58, „ ^fromboUom,insteadofG'ii read GB.. 67, „ 3, instead of H K read G K. 73, instead of Fig. 123 read FiG. 133. 76, line Sfrojn bottom, instead ofht read or. 76, ,, 2 „ „ aces ,, faces. 101, last line, instead o/" march to follow read metliod to follow 109, heading „ embratubes „ esidrasukes. Ill, last line, „ oy' read w'. Ill, fig. 223, ee' omitted. 120, line 8, instead o/ connects read conceals. 124, „ 14 from bottom, instead of 5 deep, read 5 feet deep. 140, instead of CHAWEK viii. reac? chapter vii. 142, line 1 1, instead of plane of sight, read plane of site. 148, „ 11, „ 6 read 9. 149, ,, 3, „ bends, read binds. 157, instead of chapter xi. read chapter rx. 185, line 6 from bottom, instead of resorted to. When the enceinte read resorted to : when the enceinte. 225, „ 9 from bottom, instead of marks read masks. 226, „ 3, instead of &ECTici; B. „ Section b. 227, „ 4, „ Mons. „ Mons, 233, „ 3, „ hove read have. 233, „ 11, „ Flyiny Sap „ Fhjing Sap. 234, „ 9 from botUnn, instead of 23^ h%t „ 2 J feet. 248, „ 11 from bottom, instead ofadvance ports read advanced posts. 259, ,, 21, instead of 1656, read 1856. 293, lines 4, 3, 2 from bottom, instead o/ towers contained two casemates, or subterranean, &c. &c. read towers contained casemates, or subterranean vaults, built bomb-proof; each tlauk had two casemated guns firing through embrasures 6 feet above the level of the ditcli ; making, with the two guns moimted on the platform of each tower, altogether eight pieces only for the defence of the ditch. 346, line 6 from bottom, instead of ^l read "^P , P p' 387, „ 9 from bottom, instead of thread read tread. 402, „ 10, instead o/ marked read masked. 413 to 436, heading, instead o/ bastion read bastioned. 420, line 20, „ V° read -^ 442, „ 24, instead of 14 yards read 28 yards. 25, „ ■ 16 „ „ 32 „ ... „ 27, ,. 30 „ „ 25 „ ... „ 28, „ 64 „ „ 56 „ . 29, ; 83 ;: ;; so ;; ?r 443, ' ., 5, , this read ; it. . 9; dv, rea-squaro, because the recoil is not great, as in field pieces. GARRISON CARRIAGES. Kio. 14 The carriage for howitzers is similar, but has blocks of wood instead of rear trucks, and is fui'ther strengthened by iron. Iron carriages are also employed in the colonies. (15.) Gari'ison cai-riages are raised, so as to fire over a parapet, by means of traversing platforms, of which there are three kinds. The common platform, made of wood, and sometimes of u-on, consists of two long side pieces placed upon four legs, ha\-ing trucks that ran upon a circular racer let into the gromid. On the top of each side piece is a plank for the tracks of the gun carriage to run upon, whilst a riband placed inside both pieces, prevents the trucks from running off. Those platforms traverse in front, centre or rear, and have a slope of -^ to diminish the i-ecoil. When a garrison carriage is mounted on such a platform, the two hind trucks ai-e replaced by blocks of wood. The dwarf traversing platform exposes the guns less than tlie above. The ordinary garrison carriage is used with it, but Fig. 16. 10 NAVAL CARRIAGE. has blocks instead of axle-trees. In front of each bracket is a brass truck, which is of sen-ice when the rear of the carriage is hoisted up by the truck levers. (98.) The casemate platform is low, has no legs in fi"ont, traverses on a racer let into the masonry, and has a carriage as above. The cai'riages for the transport of heavy ordnance are the slhiff cart, sU7ig waggon, platform icaggon, and trench cart. (16.) The naval carriages for heavy ordnance are distinguished into common ship carriage, rear shock carriage, sliding carriage, and jamming carriage. The light pieces have carriages similar to those of the field, besides carriages for boat service. (17.) To complete this nomenclature, we may add that mortars have no carriage: they rest on beds of iron as regai'ds the 13, 10 and 8-in., and on beds of wood as regards the Sj and 4^ in. mortars. A bolt on each side, both in front and I'ear, serves to run the mortar, which is pointed by means of a quoin, up or back. (18.) The number of horses allowed for the vai-ious pieces of ordnance viu-ies; in the service, it is found advisable not to employ more than 12 horses for the heaviest ordnance. Thus a 24 or 32-pounder carriage is di-awn by 12 horses ; an 18-pounderby 12, a 12-poimder anda 9-pounder by 8, a 6-pounder by 6. In horse ai-tillery, each horse has to draw about 4^ cwt., in field batteries 4f, and with hca\'y orcbiance, from 5| to 7 cwt. For field cai-riages, and those for light guns of position, double draught is em- ployed, the off-horse being ])laced in the shaft ; mountain ai-tiilery carriages have shafts for single draught ; for siege carriages or heavy guns of position, four horses are harnessed abreast, and there are two pairs of shafts, one for each of the inside horses. SECTION IV.— Pkojectiles. The projectiles fired from ordnance are— shots, shells, shrapnels, carcasses, and balls. The shots may be classed into round shot (solid or hollow), grajie, and common case or canister. (19.) Solid shot are spheres of cast iron, and are fired from all guns oxcei)t PUOJECTILKS. 11 shell giuis. Those for field giins have wooden sabots. Hollow shot, are hollow spheres of cast iron fired from shell guns, and are chiefly used for naval service. Their diameter is great in comparison with their weight ; and their relatively smaller momentum causes the formation of large apertures and numerous sjjlinters. ( 1.) Grape shot consists of a number of cast iron balls Fio. 17* arranged in tiers, by means of three cast iron circular plates, and a bottom plate of wrought iron, the whole being secured firmly by a wrought iron pin that passes through the centres of the plates. There are from 3 to 5 shots in each tier, from 8 ozs. to 3 lbs. each, according to the calibre of the gun. It is only fired from iron guns. Grape shot is very destructive at ranges under 300 yards, and will even produce great effect at 600 yards. (22.) Common case or canister, consists of a number of cast iron balls, placed in a tin cylinder liavmg a wooden bottom. The number and size of the balls vaiy, they weigh from 2 ozs. to 1 lb. each. A field gun canister contains 4 1 balls of 2 ozs.; a 32-poimder howitzer, fires a case containing 258 balls of 2 ozs. Canister is fired both by guns and howitzers. The case for the 10 inch (sea) gun, has a cylinder of sheet ii'on, with an iron top and bottom. Canister is effective at a distance of from 100 to 300 yards only. (23.) Shells are hollow spheres of cast iron, with a hole to receive a fuze : they were formerly filled with just sufficient powder to burst them, but at pi'esent they are entirely filled, which causes the projectile to be less eccentric, its flight to be more regular, and the fragments to have a greater momentum. The length of the fuze (33), is calculated to cause the shell to burst at the proper distance. The thickness of metal is about ^ of the diameter — to resist the shock of the dis- charge, and weighs neai-ly f of the solid shot of equal diameter. There are three kinds of common shells — The common shell, which is provided with a sabot of wood, attached by a rivet to the I)ottom of the shell opposite the fuze hole, and destined to maintain the fuze in the axis of the bore when loadinjr. 12 SHRAPNEL. When such a shell is conveyed loaded, a gutta percha wad, driven through the fuze hole, keeps the powder dry, and is secured by a metal plug screwed into the fuze hole. The naval shell is always carried loaded with its metallic fuze, and is similar to the former. The mortar shell has no sabot. The shells for the 13 and 10-inch mortars, have two small rings or slugs on the sides of the fuze hole to facilitate loading. (24.) A shrapnel shell, or spherical case shot, is a shell filled with musket balls, and a charge of powder to burst it. The thickness of the shell is about -fV the diameter, and the weight is half that of a solid shot. The bursting charge was poured loose among the bullets in the original shrapnel, which often caused premature explosions, it has Ijccn improved by Captain Boxer, who separated this charge from the balls. In the improved shell (fig. 20), the powder is placed in a cylinder of metal, and the balls are kept steady by melted rosin poured into the interstices. In a further improved shrapnel by the same oflScer, called the diaphragm shell (fig. 21), the bursting charge is separated from the balls by a partition or diaphragm of wrought iron. The balls are harder, being made of an alloy of lead and antimony ; the rosin is replaced by coal dust; and a coating of mai'ine glue inside the shell, prevents this dust from mixing with the charge, should the diaphragm give way. The bursting of the shell is facilitated by four grooves running into the interior, from the fuze hole almost to the l)ottom. The fuze hole is fitted with a mctul socket, into which the fuze is iilaced when tlio metal piny (23) used when C.VRCASSES. 18 canying the shell is removed. The bullets for field guns weigh 20 to the pound, those for heavy guns, 14. A shrapnel for a 6-pounder gun contains 29 bullets, for 12-pounders 62, for 32-pounders 151, for an 8-inch gun 338. Shrapnels do exe- cution at considerable ranges, but the fuze should be regulated so that the shell may explode about fifty yards short of the object fired at ; if either too long or too short, the effect is lost. (25.) Carcasses are shells with three fuze holes or vents ; Fio. 22. they are filled with a cei"tain composition, which being ignited by ^ -v,^^ the discharge issues in strong flames out of the vents during about / \ ten minutes, and sets fire to any combustible material it may fall on account of tlie three vents which weaken it. They are fired from any ordnance — generally mortars. (26.) Balls are of two kinds: Light-balls, — either ^roMncZ litjht (bm-ning on the ground), or suspended light (burning while sus- pended in the air by means of a small parachute, the invention of Capt. Boxer), are fired from mortars. They are made of canvass or paper, and contain a composition which produces a bright light and burns a long time. They are employed at night to discover the movements of an enemy. Smoke balls are similai" projectiles ; but the composition produces large volumes of smoke, which form a screen and obstruct the view. They are often employed to throw into mines. (27.) Hand grenades are small shells weighing 1 lb, 13 oz., filled with a bursting charge, and provided with a fuze 2| inches long. They may be thrown by the hand fifteen or twenty yai-ds, and are employed in situations where the troops using them are secure from splinters. They are sometimes quilted and tied together with their fuzes outwards, and fired at small ranges with mortars. Hand grenades are also made of thick glass. Fio. 24. 14 ROCKETS. (28.) A rocket is a cylindrical case of papei- oi- iron filled with composition ; to one end a cylindro-conoidal head is attached, while at the other end (the choke or neck) there are several apci-tures or vents for the escape of the gases produced by the combustion. A conical hollow, the base of which coincides with that of the rocket, is left empty about the axis of the composition, in order that a great surface may be ignited at the same time, thereby generating a large quantity of gas which exerts a pressure on the interior of the rocket. The pressure on the head being greater than that on the base on accoimt of the vents, the rocket moves forwards. It is fired through a tube, so that it is propelled in the required direction. A stick attached to tlie base counteracts the tendency to rotation, and maintains the projectile in its right direction. There are in the service two kinds of rockets. The signal rocket, weighing either 1 lb. or ilb., is made of paper: there is only one vent in the axis itself, and the stick of the rocket is attached to the side. It is fired vertically, and □^^SEZ3> when the composition is burnt, the bursting charge ignites the stars put into the head. A rocket of 1 to 2 inches in diameter rises from 450 to 600 yards ; if of 2 or 3 inches diameter, from 1000 to 1200. The time of flight is from seven to ten seconds, and the signal may be seen at a distance of 40 miles. The Congreve rocket, of which there are four kinds in the service, the 3-pounder, 6-pounder, 12-pounder, and 24-pounder, has a case of sheet iron. A hollow cylindro-conoidal iron head is screwed on the top, to act as shot if empty, or as shell if filled with bursting powder. Some conical heads with vents may also be substituted for the ordinary pattern, to act as carcasses. The base of the shell Fig. 26. carries a fuze, and the apex has a small hole through which the bursting chai-ge is introduced, and a bore bit is inserted to pierce into the fuze composition (33). A metal plug closes the apex. The bottom of the rocket is closed bj' an iron plate having a centre hole, into which the stick is screwed, anil five equidistant vents. The composition is stronger than that in signal rockets. They are fired, at the proper elevation, by means of iron tubes raised above ground by legs, so as to keep the sticks from touching it. The elevation is about lo for every 100 yards of the intended rango. In windy weather they should be SERVICE CHARGE. 15 Fio. 27. fired leeward. They are fired against troops presenting a lai-ge front, or are em- ployed to set buildings on fire ; but tlie accuracy of their flight cannot be relied on. Rockets are carried in the field in a special waggon attached to each battery. (29.) The charge of powder is fixed for guns and howitzers, that for mortars is variable. The service charge is in general one-third of the weight of the projectile for heavy and medium guns, and ^th for light gims. Iron howitzers have a charge of V^.th, and brass howitzers a charge of from 4th to Ath of the weight of the projectile. In ricochet fire this charge is much altered, and vai'ies from -j'^ to -jL. In the navy there are three kinds of charges, the distant, full, and reduced. The charge is contained in cartridges made of serge, which are conveyed in boxes. For the 3-pounder gun the projectile is attached to the cartridge. The ordinaiy wads ai-e junk or oakum rolled up in a cylindi-ical form, fitting the gun rather tightly, and grummet or a piece of rope formed like a ring of an external diameter equal to the calibre of the gun. The junks are used for hot shot and brass pieces. The grummets however are preferable, since they cause less deviation. The charge is ignited by means of a tube placed in the vent hole. Of tubes there are six different kinds in the service : the common quill tube, the Dutch or paper tubes, and the common metal tube, filled with meal powder, are fired with a port-fire ; the detonating quill tube, is used for guns which have a lock fixed to the vent plate ; the hammer of the lock ignites the fulminating composition on falling ; the metal or quill friction tubes contain a similar composition, and arc fired by moans of a lanyard hooked to a ring at the head of the tube ; the ring 16 FUZES. being pulled, sufficient friction is produced on the composition by a rough strip of copper attached to the ring. Finally, galvanic tubes are also used when the gmis are " proved," and ignited by means of a galvanic battery. . Portfires are of two kinds : the common portfiro burning at the rate of one inch per minute, is made of a paper case, 16 inches long, which is filled with composi- tion ; the slow portfire is paper impregnated with saltpetre. It is foi'med into a cylinder 16 inches long, and lasts from 3 to 4 hours. Quick match is cotton coated with a composition of powder and gum ; sloio match is hempen rope loosely twisted and dipped in a solution of lime and saltpetre; one yard burns three hours. Another soi-t bm-ning under water, and called " Bickford's fuze," bums at the rate of 12 feet per 5 miimtes. Shell fuzes are attached to the shells for the purpose of igniting the bursting charge at a precise moment. There are in the service three different kinds of fuzes, the time or Boxer's fuze ; the concussion or Freeburn's fuze ; the percussion or Moorsom's fuze (see 35). The time fuze consists of a conical case of icood, for land service, and of brass or bronze for naval shells. The wooden fuze contains a composition that bm-ns regularly, at the rate of one inch in five seconds, so that any length may be given to it, by merely boring a hole through the case, which will allow the flame to pass from the case to the bursting charge. There are special fuzes for common shells, shrapnels, and mortars. The naval (metal) fuzes are also of two sorts, long and short. Freeburn's concussion fuze is so constructed, that the concussion produced when the shell sti'ikes the object, drives the ignited composition out of the fuze into the bursting charge. The case is of wood. Moorsom's percussion fuze is made of metal, and contains 3 cylincWcal chambers, in each of which is suspended, by thin copper wire, a hammer, which, falling on a detonating composition, when the shell strikes an object, causes the bursting charge to be ignited. These are liable to accidents. A new fuze is now proposed ; it is invented by Mr. Pettman. 17 ,- ... 1 is : : : ;s is?^ i :s :2 t.l^- . e i "" F 3 s:. t; r.,r,r. a If g ooo H ■£ ^ ° ° . . ° . . .^ . ° ° o ooo i goo ooo oo CO oooooooo is« ;§'^s ■ 's '2 3 & li i~- -"" ■ ■" ■-" -OOO^.M-- ^ It goo oooo oo ooo OOOOOO ino oc^ — -* 00 n g y t;. Noo oooo oo OOO OOOOOO 5 1 -.1 goo oooo oo OOOO ^^^ iSS ■ ■ 'S 'S?!?? ■ 'S '2 ^ lii go ooooooooooooooo oo O O 00 ^ CO «£ = L gOOOOOOOOMOOOOOO o ooooooooo* iist^ ^222**22222 2" *«'° •gr^SiSS' ' ;r 2S2SS2 ^ si |ooo«««^i^.^SS^S^ ="-*oooooooo=,c»o=. _c _M_«, -w^-WoW I^sssssssssssg^s ^«05- -- : : : : : : : : :^ : : : : : : : = =i •I 1 5 o = 1 r . . . =l^^^ % ''/''' "t ^ u ^ u u u ^ ^ u 1 =2 o H t! . ^ lllilllllllllli lllll llllii till 2"*"»SSS?lgS3SS2 — r-. — — rtM— -nri-T 18 RIFLED ORDNANCE. SECTION v.— Rifled Ordnance. A revolution is now going on in artillery by the introduction of rifled ordnance. Not only is an increased accui-aey of fire, with greater range and penetration, obtained with comparatively small charges ; but the equipment and ammunition of field guns are much simplified, as will hereafter be explained. (34). In 1846 Major Cavalli, a Sardinian officer, invented a brcecli-loading rifled gun ; the bore was cylindrical, 6^ inches in diameter, and rifled with two grooves. At the same time Baron Wahrendorff, a Swede, invented a similar gun, with a bore of 6'37 inches. The projectile of Cavalli was cylindro-conical, that of Wahrendorff cylindro-conoidal, and both had two projections to fit mto the grooves ; their weight was about 69 pounds. Some experiments were made at Shoebm-ynoss in 1850, in order to tiy and compare these guns with a 32-pounder of 56 cwt, when it was found that for elevations under 5°, and with charges of 8 or 10 pounds, the accuracy and ranges were nearly the same. With greater elevation the foreign guns ranged further, the excess at 15° with 8lbs, charge, being 790, and with lOlbs., 1 100 yards. The gun of Wahrendorff stood well, that of Cavalli very soon became unserviceable. In 1851 experiments were made with Lancaster guns; those were service guns bored into tifled guns, the bore being an elliptical helix, the major and minor axes of which had ] of a revolution, increasing gradually from the bottom of the bore to the muzzle, and forming what is termed a " gaining twist." Tlie pi'ojectile is elliptical in section, cylindro-conoidal in form, and hollow. In these experiments, as well as in those made at Malta in 1859, it was found that the shell is liable to jam in tlio bore and burst the gun, whilst great irregulai'ities occur in the range. (35). In France some rifled gmis, of the invention of Louis Napoleon, were introduced into the service (1859), and, for the sake of economy, were obtained. AHMSTKONG tSUN. 19 l)y the transformation of smooth-bored brass pieces. They are muzzle loading, with 6 grooves, having a turn in 59 inches. The projectile is cylindro Oconoidal, and has two sets of buttons or projections, 6 in each set, fitting into the gi'ooves of the boi'e. The field shell gun (canon obusier), replaces the four kinds of ordnance hitherto employed, viz., the 12-pomider and 8-pounder guns, the 6 inch and the 24-pounder howitzers. The calibre is 3-6 inches ; the gun weiglis from 5 to 6 cwt. ; the cliarge is 1 lb. ; the projectile weighs 91bs. Instead of 9 projectiles, there are only 4, and there is but one sort of carriage and ordnance. There is also a siege gun of tlio calibre of a 12-pounder. (35). Tho Armstrong gaa, proposed in 1854, is now adopted in thcsei-vice; two batteries of 12-poundcrs, of 6 cwt., were sent to China in 1859, and forty 100-pomiders were lately sent to Portsmouth. The Armstrong gun is made of strips of wrought iron, wound spirally round and welded together, as in sporting gun barrels, by which process the strain arising from the discharge is received by the metal in the direction of its fibres, and, therefore, in the direction in which it has the greatest tenacity. The bore is cylindrical, with a chamber somewhat larger to receive the charge and projectile. The number of grooves varies with the nature of the gun, and often exceeds 40. They have one turn in twice the length of the bore. A breech piece, with a mitred face, fitting exactly into a similar face at the end of the bore, carries tlie Fm. 32. vent, and is di-opped into a recess, thereby closing that bore ; the fitting surfaces arc of copper. A cylinder of iron, with a screw turned on the outside, works in a female screw in the breech, and presses tightly the breech piece. The projectile is hollow, and may servo as shot, shell, case, or shrapnel. It is a pointed cylinder, formed of 42 cylindro-segments of cast-iron, externally coated 20 ARMSTRONG GUN CARRIAGE. with lead. When fired, the lead is crushed into the grooves, so that there is no windage, the point of the projectile remaining foremost dui-ing the whole time of flight. This result permits the application of a percussion fuze to the point when the projectile is used as a shell. The point is therefore provided witli a female screw, to receive a plug, a time fuze, or a percussion fuze, accox'ding as the projectile serves as shot, shrapnel, or shell. The charge of powder is about ^ that of the projectile. Tho carriage is similar to that of a field gun, but lighter. It has in addition a mechanism A B, which allows minute alterations in the pointing. A screw, turned by a handle, is connected by a bai- with moveable trunnion holes, so that a horizontal motion round a centre between them may be given to the trunnions of the gun. It is also provided with an improved tangent scale. WIIITWOR'l'II GUN. 21 The 12-pounder, of 6 cwt., has a point blank of 300 yards ; the ranges are with 1°, 700yai'ds; 2o, 900; 3°, 1,200; 4o, 1,600; 5°, 1,900; 6°, 2,200; 7°, 2,400; 8°, 2,800; 9o, 2,900. Several other calibres :u-o likely to be adopted. The lOO-pounders, 10 feet long, weighing 80 cwt., are intended for the navy, for coast defences, or for garrison, and whenever very powerful ordnance are required. The 40-pounders, 10 feet long, weighing 31J cwt,, will most probably be employed as siege, garrison, and navy guns, and for coast batteries. The long 25-pounders, 8 feet long, weighing 16^ cwt., and the short 25 pounders, 5 feet 6 inclies long, weighing 12| cwt., are intended, the first for guns of position, the second for boat service. The 1 2-poimders, 7 feet long, weighing 8 J cwt., are for field guns, the projectile weighing 121bs., for field batteries, and 9lbs. for horse artillery. The 6-pounders, 5 feet long, weighing 3| cwt., are for mountain service. (36). Another breech-loading rifled gun, due to Whitworth, is now competing with the Armstrong. There is a 3-pounder, of 2081bs. weight, a 12-pounder of 8 cwt., and an 80-pounder of 80 cwt. The bore is an hexagonal spiral, the inclination of the spire varying with the diameter; the twist is rather rapid, ui order to overcome the tendency of the projectile, which is long, to turn over in its flight. The breech is closed bj' a cap, which screws on the outside, and works in an iron hoop, attached by a hinge to the side of the breech. The cap is opened back for loading, after which it is shut like a door, and scciu-ed on the breech by a handle made for the purpose. The vent is in the centre of the cap. The projectile is hexagonal, and of cast-iron. The charge is ~. The range and accuracy of tliese guns is said to be very great, the 3-pouiider carrying above 5^ miles. (37). In 1851 the old musket was replaced by a rifle; and in 1853 entii'ely superseded by the Enfield rifle. It is 6 feet 0*5 inches long, including bayonet, and weighs 9 lbs. 3 ozs. The length of the barrel is 3 feet 3 inches ; it weighs 4 lbs. 2 ozs., and its bore measures -577 inches: it has three grooves, each forming a spiral of one tiu-n in 6 feet. It is sighted to 900 yards, but its practice is good at larger ranges. The charge of powder weighs 2.^ drams. Rifle corps and sergeants of infantry have a shorter rifle, with sword bayonet: its length is 5 feet \\\ inches, it weighs 9 lbs. llj ozs., and tlie barrel measures only 2 feet 9 inches. It is made exactly on the same principle, and is u.sed witJi the same ammunition as the former. The bullet is olonirated, -55 inches in diauietir, and weinlis 530 ifniins. 23 :nfieli) kiflk. (38). Fio 37. 'P Tho penetration of the projectile exceeds that of the old bullet ; at iOO yards it goes through 19 inches of stiff clay, and at 30 yards passes through 12 planks of elm half an inch thick, and placed half an inch apart It is only step by step that this improvement of the rifle has taken place. In 1827 Mr. Delvigne, a French officer, invented a rifle with a small chamber at the bottom of the bore ; the spherical bullet fitting loosely in the barrel, rested on the shoulder of that chamber, and was expanded so as to fill the grooves by a smai't blow from a heavy ramrod. This, however, disfigured the bullet, and in 1842, Colonel Thouvenin, of the French service, attempted something else. A "tige" of steel was screwed to the bottom of the bore ; the charge being placed round it, and the spherical bullet on the top, it was expanded into the grooves by a blow. The projectile receiving the impulse obliquely could not give accuracy. These two rifles had this serious inconvenience, that the bullet could not be Fig. 38. fixed to the cartridge ; but Mr. Delvigne introduced a cylindro-ogival bullet, with a groove round it to fix the cartridge, and in 1846 this projectile was adopted in J'rance, together with the " carabine a tige ;" the head of the ramrod being scooped out to fit the point of the bullet while loading. The tige frequently breaking, and the barrel rapidly becoming foul, a new bullet, of the invention of Minie, soon obviated these defects, and the tige was dispensed with. Minim's bullet is cylindro-conoidal, with a conical hollow at the base, into which is fitted an iron cup. The powder acting on this cup (fig. 39), di-ives it up the narrow end of the hollow, and causes the surface of the lead to expand into the grooves. It was introduced into England in 1851, but in 1853 was replaced by the Pritchet bullet (fig. 40). This projectile had no cup, and was made of such a length that the powder acting suddenly on its base, drove it up slightly, before the inertia of the point was overcome, thus causing it to expand into the grooves, neai- its shoulder, the hollow being merely intended to throw the centre of gravity forward. It, however, fouled the piece, and Colonel Hay improved it by introducing a plug of box wood into the hollow (fig. 41); this prevents the sides of the bullet from collapsing when it leaves tho barrel, and is found to prevent the barrel from fouling. z\ a I'lMTCHET nULKET. 23 Tlie Pritchet bullet, improved by Colonel Hay, is now employed in the service. Other projectiles have been proposed — Colonel Jacob's (of the Bombay Artillery) bullets (fig. 42) gave long ranges, but requireil great charges. A solid bullet, Fio. 42. Fio. 43. A (fig. 43) with two deep aninilar grooves, invented by Wilkinson, has been adopted in Austria. Mr. Whitworth's bullet and rifle are on the same principle as his rifled gun, &c. (39). Besides the Enfield rifle there are in the service : the Lancaster rifle, employed by the corps of Sappers. It is made on the same plan as his rifled gnns. The total weight is 9 lbs. 2 ozs., the length of barrel is 2 feet 8 inches, that of the sword bayonet 2 feet. Its range is good, and as the bore is smooth it does not foul, but the bullet is liable to strip. There are also the Artillery rifle, the revolvers of Dean and Adams, a cavalry carbine, and some breech-loading cai-bines on trial. The number of rounds carried by each man is 60, together with 75 caps. They weigh 5 lbs. 8 oz. The I'eserve for small arms' ammunition is divided into three parts : the 1st and 2nd reserves, conveyed in ammunition wagons, are attached to the field batteries of each division. The wagons are provided with ci-adles and ladders to transport the ammunition wherever required. The 3rd reserve follows at two days march in the depots of the military store department. SECTION VI.— Gunnery. (40). The point blank range of a gun is the range a h obtained at the first graze of the shot, when the piece placed on its carriage is fired with the service Fig. 44. ^ charge, on a horizontal plane, the axis also being horizontal. A gun is " laid point blank" when the production of its axis will pass tlu'ough the object aimed at, whatever be the elevation or depression with the horizon. (41). As the axis is not visible, its position must be obtained practically: this is done by means of the line of metal or visual line joining the notches i-ut on the 24 GUNNERY. highest points of the base ring, and the swell of the muzzle ; when the trunnions are horizontal, this line is in the same vertical plane with the axis of the gun. In guns which have no dispart patch, when the line of metal is pointed upon an object, the axis passes over the object aimed at, and the elevation thus obtained is called line of metal elevation; it is 1° in light field giuis, l^"' in medium ditto, 1^0 in ordinary iron guns, &c. (42). As the charge of a gun is fired, the initial velocity of the projectile is constant, the range will therefore depend upon the inclination of the axis to the ground. The action of gravity causing the projectile to descend continually after leaving the bore, it is necessary, in order to strike an object, to direct the axis at a point more or less above the object, according as it is more or less distant. The elevation of the axis is obtained by means of a tancjent scale, of which there are several sorts in the service ; the ordinary scale consists of a rod, which, sliding up and down in a groove behind the vent, can be fixed in any position, by means of a screw. It is divided into quarter degrees, as far as 8°. The line of sight is the line passing tlu-ough the top of the tangent scale, the notch of the muzzle and the object fired at. ;ntcf/'> Trajectory — ^.^^^^ The aiKjk of elevation is the angle which the line of fire, or axis produced, makes with the line of sight. The angle of elevation may be given to guns by other means than the tangent scales : thus in field guns it may be obtained as far as 3° by the quarter sights, or by cuts on the sides of the base ring ; the top notch, with another on the swell of the muzzle, giving a line of sight parallel to the axis. A spirit level quadrant, or a gunner's quadrant, may also be emj)loyed. (43). Trajectory is the path described by the centre of gra% ity of the projectile ; it intersects the line of sight in two jioints, one near the muzzle, the other at the object fired at. (44). Mortars are laid by means of a plummet, held in the hand just behind the piece; the string being made to coincide with two pickets planted on the parapet, in the direction of the object, the mortar is traversed until the line of the plummet covers the central lino of the mortar, indicated by a iioteli ). The supenor slope DH slants towards the country with an inclination ,!, in order to enable the defenders to fire immediately in front, and to see the assailants until they descend into the ditch. It may occasionally slant a little more, but it will have the inconvenience of weakening the crest of the parapet. This slope is also called plongee, or plane of fire, because it is from it tliat the fire is poured out. In fortification, instead of measuring the inclination of a slope by the number of degrees it makes with the horizon, or with its base, we obtain it by dividing its height or fall by its base, so that this inclination is reju'eseuted by a fraction "hose numerator is equal to the height, and the denominator to the base, "o. 58. Thus if AB = 1, and BC = 2, the slope AC is V.,^^^ said to be at i ; if MN = 3, and NP = 2, the slope [____j_^^^2^p MP is at f. A slope at \ is often called a slope at 45°. Most military authors on the continent take for the fraction the base divided by the fall ; but in reading these 'fractions no mistake can be made if the fundamental form of a parapet is well understood. The defenders are posted on the Banquette KE. It is level or slightly inclined to the rear, to carry off the water; it is 3 feet wide, or 4 feet 6 inches when destined for two files of men, and stands 4 feet 3 inches below the crest of the parapet, this being the most convenient height for a man to fire over and at the same time remain covered. To ascend from the interior of the work, or Terreplein, up to the Banquette, a slope of Banquette AK at ^ is constructed. A steeper slope would be inconvenient to ascend the banquette, and a more gentle one would occupy too much space inside the work : in fact, this slope is replaced by steps, whenever it is important to economise space. The parapet is connected with the banquette by the interior slope DE at f, and with the ground on the outside by tlie exterior slope HB at \. With an interior slope less steep than.f, the men would be more exposed, especially to pitching fire, and too far from the crest to rest their muskets on the superior slope. A vertical slope would bo preferable, but earth would not allow this, and even at f it requires (142) artificial means to support it. The exterior slope in works destined to stand for some time should be made I) M 34 THE DITCH. at -fT7) the slope which earth will generally assume ; it corrcspomls to an angle of 35o, The intersection of the superior and interior slopes is called the interior or superior crest, or merely crest, also line of fire ; that of the superior and exterior slopes is named the exterior or inferior crest This is the shape which experience has taught us to adopt in the field, when we are on level ground, but it should only be considered as a type (154). In permanent fortifications we find also a rampart AB or large mass of earth of various heights, and its slope of rampart AC, at |. This additional height is necessary to protect the buildings, and to command the countiy. (52.) The ditch is comprised between two slopes ; that next to the parapet AB is called the escarp ; that towards the country CD, the counterscarp ; the levo' part BD is the bottom. A ditch may have a triangular profile, such a one is found advantageous when it is without flank defence, because the assailant cannot easily form in it. The inclination of the scarps varies according to the nature of the soil, from I to ^. Escarp. Counterscarp. Berni. Strong soil -J^ A 1 foot Ordinary soil . . . . | a 2 „ Sandy soil i \ o „ DKPTii. 3n but the escarp, having to support all the covorini;le according to the direction of wliicli ;i face is flanked, are called lines of defence. Such ai'c AB, AC. If the face that is flanked is not contiguous to the flanking one, the line AC, is still called line of defence. The angle B A C, is in both cases called aiujle of defence. Vm. 70. Fig. 71. Should the angle he small, the men would fire on their own party ; and if it were very large, the flanking could not be efFoeted except by an oblique fire. Therefore, limits have been fixed at from 90° to 120° for these angles. Fig. 72. As the superior sloj)e of parapet is inclined at i, the shot that follows the line AB, meets the ground at a distance CD from the crest, equal to six times the com- mand ; and if the |)arapet belongs to the face of a re-enterigg angle, the defenders cannot see the ditch before them for a distance MN, equal to six times the relief. I 3 4!) -? DEAD ANGLE. '' ■i <> ir.t'^' Tliis space wliicli cannot he seen by the defenders, is called dead angle. It is a serious incon\enience of the re-entering angles. With the ordinary relief of field works, the distance CD is about 15 yards, that of MN 30 yards. (59.) Salients are points of attack : we obviate the inconvenience of the undefended space which they necessarily present, by artillery in the capital, by accessory means, and, above all, by flanking. The critical moment is when the enemy arrives at the comiterscarp and descends into the ditch ; shovdd he then be unexposed, he may mine the work, or collect in sufficient force to assault it vigorously. We have seen that along every flanked face, AB, there is a dead angle occupying nearly 30 yards ; if the faces then are shorter than 30 yards, no part of the ditch is seen by the defenders. As, however, the enemy in reach- ing the salient B must be seen in the ditch, we are obliged to make the faces longer than 30 yards. The inferior limit of faces destined to flank each other, has sometimes been fixed at 15 yards, but this dimension only permits a sight of the top of the counterscarp in front of the salient, and the whole ditch is dead. It should not, therefore, be adopted for works from which a vigorous defence is expected. As for flanks, or lines of parapet intended to give a flank fire on the side of a work, they may be made as short as convenient. The maximum length of the faces of a re-entering angle, or what is the same, of lines of defence, had been fixed at 180 yards, because the fire of the old musket was too uncertain beyond that range. The introduction of the Enfield rifle, will permit an increase of that distance, but it will not produce a great alteration in the faces of field works, because there is seldom any occasion to make them longer than 100 yards. In some cases, howe\'cr, it may enable us advantageously to modify the outline, as we shall see. (60.) The fundamental principles of all fortification which wc now recapitulate, have been deduced fi-om the nature of the arms employed, and are rendered evident by the most simple considerations. PRINCIPLES. 41 The extent of a work must be proportioned to the niunl)or of mon intended for its defence. The outline must give as much direct and Hanking fire to bear on the point of attack as possible. The salient angles must never be less than 60o. The angle of defence must bo between 90° and 1 20°. The length of the lines of defence should not be less than 30 yards, and should not exceed the range of musketry. {See 435.) A work in which all these conditions are observed is called a good work ; but hero theory must give way to practice : the ground to be fortified is given, and wo must make the best of the foregoing principles ; but it is not always possible to apply them all at the same time. Although in theory a work without flanking is deficient, yet the conformation of the gromid and the destination of the work may bo such, that this consideration becomes of less importance, and the work may be nevertheless a good one. jj ^ :tt c6lA kJ 42 CHAPTER III. ON THE DRAWING OF FOETIFICATION. SECTION I.— Scales. (61.) The representation of a work of Fortification can be made of different sizes according to the end in view, it being clear that tlie greater the accuracy required, the larger the drawing should be. The length of a dimension of the di'awing, compared with that of the corres- ponding dimension of the work on the ground, is called the scale of the drawing. Thus, if a face eighty yards in length, occupies but one inch in the drawing, the scale is that of one inch to eighty yards. Again, if a wall a hundred yards long is represented by a line of 5 inches, the scale is that of 5 inches to 100 yards, or of one inch to 20 yards. As one inch represents 20 yards, or 20 x 36 =: 720 inches, we may say that every length on the ground is represented in the drawing by a dimension 720 times smaller, and that the scale is of y-i-^. These two methods of exjiressing the scale are identical, and we may adopt one or the other. A scale of ^nrxn-oj signifying that the dimensions on paper are 63,360 times less than their corresponding ones, on the ground, it follows that one inch represents 63,360 inches, and that the scale is of one inch to 63,360 inches or one mile. Supposing that a drawing is to be made on the scale of j-h-u- If wo draw a line 5 inches long, and divide it into 10 equal pai-ts, it is clear that each pai-t will represent 10 yards, since 5 inches stand for 100 yards. If we further sub-divide each part into ten, the new subdivisions will each represent one yard. A line, thus sub-divided, is called the scale of the drawing, and we can by means of a pair of compasses, obviously use it on paper, as we would on the ground use a chain or any other instrument. To construct that scale properly, draw in pencil three parallel linos, about -rV of an inch apart, and mark off on the bottom line five inches. Divide that length SCALES. 43 into ten equal parts, and tlio k'tt-hand division into ten parts again. To divide a line AB, into a given nuniljer of equal pai-ts, draw through the extremity A a line AC, making with AB any angle ; on AC mark off any length A d, and take as many parts A dzzdd'^d'd" as there are divisions to he made on AB. Join tlie last point C with B, and through d', d", d"', &e., draw parallels to B C. these parallels intersect AB in points 1, 2, 3, 4, &c., equally distant. Through all these points of division, draw perpendiculars to the parallel lines, limiting those that mark the primary divisions by the top line, and those of the secondary divisions by the middle line. The perpendicular corresponding to the 5th or middle subdivision, may be carried half way between the two upper parallels. In inking the scale omit the top line, and draw the lower one thick. In order to Yards. IP 6 o xo ao so *o so 60 70 80 so i'n n I n , , I \ \ T I T 1 I ' "1 1 make this scale convenient for taking off distances, wo mark at the point where the primary and secondary divisions meet, and we number successively 10, 20, 30, &c., from left to right. The secondary divisions are numbered 5 and 10. The unit of measui'e, " yards" in this example is written at the right, and the name of the scale, either scale of ^l ^ or scale of one inch to 20 yards, is wTitten above it The method of using tliis scale is very simple. Suppose we want to take off 36 yards ; jilace one point of^the compasses on the primary division marked 30, and the other point on the 6th sub-division, the length included between the two points will be 36 yards. Conversely, to value a dimension of the drawing, take it with the compasses, by placing one point on the division 0, and reading the figure corresponding to the right point. If this point does not coincide with a primary division, move the compasses to the left, until the right pomt corresponds with the nearest division, the left point of the instrument will then mark the required sub-divisiou. 44 SCALES. As the theory of scales should be thoroughly understood liefore any attempt to draw a fortification is made, we shall give a few examples to render the subject familiar. I.— To draw a scale in which 360 yards are represented by 2-7 inches. The length of a scale vai-ies generally between 4 and 6 inches, and since the number of units which it represents should always be a simple multiple of 10, 100, 1000, &c., simple for the sake of convenient divisions, let us assume that the scale represents 600 yards. From the proportion 360 : 2-7 : : 600 : x, we find that 600 yards will be represented by -^g^ = 4'5 inches. Draw therefore, as above, three parallel lines, and take on the lower one a length Fio. 78. Scale of ^^. ^^^^ 100 60 O 100 aOO 300 400 soo hm i Imm I I I I I I of 4 -5 inches, which will represent our 600 yards ; d i vide it into six equal parts, each of which will represent 100 yards ; sub-divide the left hand part into ten, each of the sub-divisions denotes 10 yards. These secondaiy parts are too small to be further sub-divided, the scale cannot, therefore, show parts less tlian 10 yards ; but if it were necessary to mark oflP single yards, we should have recourse to a method which we shall hereafter point out. {See 62.) The figuring of this scale is done exactly as in the former example. As for the i-epresentative fraction, we observe that 360 yards or 12,960 inches ai-e repre- sented by 2-7 inches ; the proportion between a dimension of the cb-awing and the actual size, is 2-7: 12,960 or 27: 129,600. Therefore the representative fraction is ,.,lluo or T-gVo • II. — To construct a scale of , „',;o , to measure yards. In this case, 6 inches representing 6 x 1260, or 7560 inches = 210 yards, we shaU have a scale of convenient length if we represent 200 yards. As 200 yai'ds or 7200 inches are represented by i^^:=5-71 inches, set ofi" 5-71 inches on the bottom line, divide into twenty equal parts, and subdivide the left-hand division into ten equal parts, each secondary division shows single yai'ds. The only difS- Fio. 79. Scale of jJj^. -I \- culty is to draw with sufficient accuracy 5-71 inches. Now 5-71 inches is the same as 5v„',. 01' t' '. inches, or, dividing numerator and denominator liy 2, the same as SCALES. 45 285 1, fiftieths of an inch. If we have therefore a scale on which are found fiftieths of an inch, it is easy to take off that length as well as any other expressed in hundredths of an inch. Such divisions of fiftieths of an inch are usually found on protractors, or Marquois scales (64). III. — To construct a scale for a drawing in which we find that 1', inches re- present 17 '5 feet. Tiike 60 feet as the whole length of the scale ; 17-5 : 1-5 : : 60 : x, then 60 feet are represented by — — — =: 5-14 inches. Set off 5*14 inches, divide into six equal parts; subdivide the left-hand division Fio. 80. Scale of YTo- I , r o 10 30 30 40 .,., l ,..,l ' I I - I — '. nto ten : the secondary divisions will show single feet. As 1 7*5 feet zz 2 10 inches, the representative fraction is ^rj:= t-tj. IV. — To draw a scale of ^V to measure feet and inches. 6x12 72 Assume 6 feet as the whole length: these will be represented by — -_z=_ = 4-8 inches ('fl^). Set off 4*8 inches, divide into six equal parts ; the divisions mark single feet. Subdivide one part into twelve, and we obtain inches. Fio. 81. Scale of Vt- Fee T i,M., i t I I I I V. — To draw a scale of 8 inches to 1 mile, to measure yards. Since 8 inches represent 1760 yards, 4 inches stand for 880 yards, and we shall have a convenient length by assuming 1000 yai-ds. Now, 1760 ■: 8 :: 1000 : x, therefore 1000 yards are represented by — ^^-— — = 4-54 inches =tir_ inches. 1760 50 Dividing this length into ten equal parts, and subdividing one of them into Fio. 82. Scale of TfgVoi "'' ^ inches to I mile. Yards. T„fL„ i T -T — 4 ° T T' T T ^r H " ten, the secondary divisions show 10 yards. Smaller parts cannot be -shown (see 63). The representative fraction is ,; ^^^ „ = .,,',; „ . 46 SCALES. VI. In a French drawing we find a scale of French metres in whicli 70 metres measure 6"3 English inches. Construct a scale of English yai-ds for that drawing, 1 metre being equal to 3-270 English feet. 70 meti-es=: 70 x 3-27 English feet _ 70 X 3-27 3 76-3 : 6-3 : inches. 76'3 yards, which we find represented by 6*3 inches. Putting 3 : X, we find tliat 60 yards are represented by = 4'95 This length divided into six equal parts, shows parts of 10 yai'ds, which Fig. 83. Scale of ^1 2746-8 inches, the representative fraction will be subdivided into ten gives single yards. As 70 metres = 228-9 English feet ■= 6-3 _ 63 _ 1 2746-3 27468 " 436 (62). When a scale is required to show minute lengths, the former method is no longer available, and we have recourse to diagonal scales, the construction of which will be explained by one or two examples. I. To draw a scale of j-nVr, to show single yards. 400 X 36 , „ . 3000 Assume a length of 400 yards : it will be represented by . Draw a line 4-8 inches long, divide it into four equal parts ; subdivide the left- hand part into ten; then each subdivision shows 10 yards. Figure the scale as an ordinary one, 100, 80, 60, 40, 20, 0, 100, 200, 300. Parallel to it draw ten Fig. 84. '■^'•"'^ "/Woo- *T_\ L __1 \.el_ 6 Xa lOO 80 Co 40 parallel and equidistant lines about -^ of an inch apai-t. Through tlie points of primary division, 100,0, 100, 200, 300, di-aw perpendiculars intersecting the ten parallels, and number the left-hand perpendicular as in the diagram; Join the last point 10 to snlKlivisioii 90, and through subdivisions 80, 70, CO, &c., draw parallels to 10-90, crossing the former ones diagonally. The scale is now complete. The diagon.al lines, being parallel to one another, intercept segments of 10 yards on the other pai-allels; but between tlie perpendicular and the diagonal the intercepted segments are of different lengths ; and fi'om a well known princiido of geometry, the part intercepted on the first parallel is -'„ of a sul)division, and represents therefore one yard ; on the second parallel it is -^,;, on the thiixl -\-, and so on, the figures written on the left hand perpendicular indicating the number of yards intercepted. To show liow to use this scale : suppose it is required to take off 268 yards. Place one point of the compasses on the intersection of the parallel numbered 8 and the perpendicular 200, and put the other point on the intersection of the same parallel with diagonal 60. The legs of the compasses will thus include 268 yai'ds, viz., 200 from a to b,8 fi-om b to c, and 60 from c to d. II. To draw a scale of -p^^ to show feet and inches. 50 X 12 Assume 50 feet. This is represented by 100 6 inches. Draw a line of six inches, divide it into five equal parts ; the last part sub- divided into ten will show single feet. Figure the line 10, 8, 6, 4, 2, 0, 10, 20, 30, 40. In order to show inches, we must divide the foot into 12 equal Fio. 85. Scale of yi^. M M 1 M M ' 1 1 1 1 1 1 1 1 1 1 1 1 1 "l^H" H~l~"Hrl" ;b 1 1 1 111 1 ~H — ^^rri f ..11 11 \Vr[VW\-\ « parts. Draw, therefore, 12 equidistant lines parallel to the first: through the points 10, 0, 10, 20, 30, and 40, erect perpendiculars ; number the left-hand perpendicular, 2, 4, 6,8, 10 and 12. Dravy the diagonal 12 — 9, and parallels to it, as in the former example. It is readily seen that to measure 26 feet 7 inches, for instance, the compasses must include the distance a b. The selection of the scale on which a drawing is to bo made is not altogether arbitrary, for it depends on the one hand upon the dimensions of the paper, and 48 SCALES. on the other upon tlie degree of accuracy required in the representation of tlie work. Wlien we have to represent a work 250 yards long, it is evident that if our sheet of paper is only 8 inches long, we cannot employ a scale larger than 8 inches to 250 yards. Any scale smaller than this would, on the contrary, enable us to represent the entire work. Still, if we were to emjjloy a very small scale, we should fall into a serious difficulty, because small details could not possibly be represented. The accuracy required must therefore be* our guide. In the scale of 1 inch to a mile, for instance, a face of 10 yards would be represented by -rf^ of an inch, a dimension far too small to be appreciated or represented. If it were, however, necessary to rejiresent everything within ten yards, which scale should we select? To answer this, let it be observed, that in supposing a drawing mathematically correct, we unavoidably commit, in reading it, an error due to the imperfection of our sight. We cannot appreciate a dimension less than -pLj of an inch, because our eyes cannot distinguish whether the points of the compasses are within -p^ of an inch too near, or too far apart. This un- 1760 certainty in reading amounts to "Joo — ^^^ yards, in the scale of one inch to a mile. If the drawing must enable us to appreciate 10 yards, the scale shoidd be such that -pi^j of an inch does not represent more than 10 yai'ds ; therefore the scale must not be less than 1 inch to 1000 yards. For the same reason, the scale in which a drawing is made shows at once with what degree of exactitude it may be read. In the scale of 4 miles to an inch, the smallest distance we can possibly measure is rnn~ ~ ^^ j^ards. We have taken for granted that — l_ of an inch is the smallest dimension which we can appreciate, although divisions of an inch into 600 parts have been obtained. In drawing, however, such accuracy becomes an illusion, inasmuch as the paper on which we draw contracts and expands under the influence of heat and moisture, and -^-^ of an inch is already very small. (64). All excellent selection of scales is found in the instruments called " Marquois Scales," which consist of a right-angled triangle and two flat rulers of wood. These instruments are very handy for drawing parallels and perpendiculars with. If it is required to draw through point C a parallel to A B, jilace the bevelled edge of the triangle on A B, apply a ruler R R to the hypotlienusc, and MARQUOIS SCALES. 49 press it down with tiie left hand to steady it ; slide the triani;le with the right hand till the edge [)asses through C, when A' B' will be parallel to A B. If a perpendicular has to be drawn to A B through a point C, place the bevelled edge of the triangle on A B, apply the ruler as before, and slide tiie ti'iangle till the small side D E passes through C, when C D' will be perpendicular to A B. Instead of applying the bevelled edge on A B, the small side might be placed on it, and the triangle slided till the bevelled edge passed thiough C. These two operations can, however, be made with any triangle and any ruler. What distinguishes the Marquois instrument, and renders it especially useful for drawing fortification with, is that it is so constructed as to enable us to draw ]iarallels at any required distance without the help of compasses. For this purpose, the triangle has its longest side pi'ecisely equal to three times its smallest, and is marked with an index on its middle. The rulers, one foot long, have two scales on each edge ; an ordinary scale a little inside the edge, and an artificial scale on the edge itself: the divisions of the artificial scale are made exactly three times as long as those of tlic ordinary or natural scale, and are exclusively intended to be used in sliding the triangle. The graduations of this outer scale extend botli wavs from the ci'ntre. .)() MARQUOIS SCALES. If we have to draw a line parallel to A B, and at 40 feet, for instance, from it, select the ruler that can-ies the natural scale employed for the drawing, and proceed as in the former proljlem. Place the bevelled edge of the triangle on A B, and adjust the ruler so that an exact division of the artificial scale coincides with the index o. Slide the triangle until tiie index has moved from o to o' along forty divisions. The line A' C will be parallel to A C, and at 40 feet fi'om ii This is easily proved from the similitude of the triangles A C H, A P H'. Since AH = 3CH, therefore AH'=3PH', but A H' = AH + H H' = A H + oo', therefore AH+oo'=3PH'=:3 (C'H' + C'P) = 3 (C H + C'P) and sub- stracting from both sides the equals A H and 3 C H, there remains o o' =r 3 C'P. The artificial scale being three times larger than the natural, it follows that C'P is precisely equal to the distance required. In the scale mai-ked 50, we find that each subdivision represents -^ of an inch, and we employ it, as stated above, (61. II.) to measure lengths expressed in hundredths of an inch. In example 3, we had to set ofi' 5"14 inches or -f-i-i = "i^ inches. Placing one point of the compasses on division 25 of the 50 scale, and the other point on subdivision 7, we have the required length. The Marquois scales usually contain the scales 20, 25, 30, 35, 40, 45, 50, and 60. Taking one of the subdivisions to represent one yard, the scale 20 = -^ ; 25 =: ^rTM7 ; 30 = -nnrr,- ; 35 = Wrtt; 40 = ttVb-; 45 = -ruW ; 50 = -j-^; 60 = .rrViT- If one subdivision represents one foot, the scale 20 =: ^.j ^ ; 25 -j ^^ ; 30 = -jj^ ; 35 := ^^ ; 40 = -f-i^ ; 45 = ^rhr 5 50 = -^',-0 ; 60 = ^4-^. Again, taking one of the primary divisions for one yard, wc should have the scale 20 =: ^V ; 25 =-^; 30 = -tAtt, &c. (65). A protractor generally consists of a semicircle of thin transparent horn. It is, however, occasionally made of brass. Its circumference is subdivided into degrees or half degrees, and its graduations on the outer arc extend from right to left from 0^ to 180, whilst on the inner arc, corresponding to the rest of the PROTRACTOR. Fio. 90. V / >-•' circumference, the graduations from right to left run from 180° to 360°. The margin A B is pai-allel to the diameter 180—0. The instrument is frequently made of a rectangular piece of ivory, divided "^ ajid graduated from left to right,'as in the diagram, the margin coinciding with the diameter 0—180. Whatever be its form, this instrument is employed to measui'e the angles of a drawing or to construct (protract) the angles we require. To measure the angle formed by two given lines A C, C B : place the centre of the protractor on the Fig. 92. vertex C, and the radius o, on one side C B, the other side will indicate in D the value of the angle. To draw through a point C, a line inclined to C B at a given number of degrees : place the centre of the protractor on C (fig. 93), the radius o coinciding with C B, make a dot D at the graduation required, and draw C D. If the point given is not in the line, place the radius marking the numl>er of degrees required on -the given line A B, and slide the protractor along that line PROJECTIONS. Fio. 93. until the margin passes through C, keeping the radius carefully on A B ; and (U-aw C D. SECTION II —Projections. A work of Fortification is bounded by a certain number of surfaces, whose intersections are lines. To represent a work, we must, therefore, find X means of constructing a drawing, which will show these lines of intersection in their relative positions. As a line may be considered as composed of a series of points, the first step that must be taken is the representation of points. This is done by projections on planes. (66). The projection of a point on a plane is the foot of the perpendicular drawn from that point to the plane. Thus, if A be a given jjoint in the space, and M N any plane, the perpendicular A a meets the plane in a : and this point a is called the projection of A on plane M N. But it is obvious that any point of the line A a, B for instance, will have for its projection on the plane M N the same Fio. 95. point a; tliercfore, one ]ir()jei-tion on a fixed not sufficient to represent a PROJECTIONS :);$ given point : all we can conclude from it is, that the point is situated somewhere in the line perpendicular to the piano through a. Suppose now a second piano N P standing?anywhere at right angles to M N, if Fio. 96. A a' he drawn perpendicular to it, a' will he the projection of A on that plane, and, as before, we know that A must bo somewhere in the perpendicular to N P (h-awn through a'. The projections, a, a', on two fixed planes, will determine pre- cisely the position of A, smce the two perpendiculars erected through a, a can meet only in one point. It is found most convenient to take for planes of projec- tions a horizontal and a vertical one ; the projection on the horizontal plane is called plan, that on the vertical is called elevation. If M N is horizontal, N P vertical, a is the plan, a' the elevation of A, and the line N O, in which the planes of projection intersect, is called the ground line. The projection of a line on a plane is obtained by projecting every point ; thus, if from the points A, B, C, &c., of the curve ABC perpendiculars Fio. 97. A a, B b, C c, &c,, are let fall on the plane M N, the line a b c is the pro- jection of ABC, and if M N be horizontal, a b c is the plan of ABC. As the projection of a straight line is also a straight line, if we only Fig. 98. 54 PROJECTIONS. and b, and join a b, we obtain at once the project the points A and B, in projeftion. One projection is not sufficient to determine the position of a line. If we take C and D on the perpendicular A a and B b, the line C D will have also a b for projection ; any cm-ve E F G, situated in the vertical plane A. aB b, will have likewise a b for projection. We must, therefore, as we have seen for one point, adopt two planes of projection. If M N be horizontal and N P vei-tical, the plan a b and the elevation a b' perfectly determine the jiosition of A B, since it is the intersection of the planes a A bB perpendicular to M N and a' A b' B, perpendicular to P N, which planes can have but one intersection. Whatever may be the position of the horizontal plane of projection, the plan will invariably be the same, but the elevation will vary with each position of the vertical plane. Nevertheless, the elevation on any vertical plane, together with the plan, will perfectly determine the line. In the annexed diagram, for instance, the plan a b and elevation a' h' represent A B, but « b and «" b" rejjresent it as well. >ROJEOTIONS. Fiu. lul. A work of Fortification is bounded by seven planes, the slope of banquette, the banquette, the interior slope, the superior slope, the exterior slope and the two limiting slopes. These slopes intersect in 18 straight lines, which meet one another in 12 points. The projections of these 12 points, properly joined, give the projection of the whole work. Imagine a horizontal plane M N situated l)eneath the parapet, and two vertical planes N P, M P beside it; from the 12 points draw perpendiculars to the three planes, and join their projections as tlic}- arc in the work ; and wo tlms obtain a plan and two cle\ations. r,6 PROJECTIONS. Before showing the relation between the \)\an and an elevation, let us see how this method of projections can be applied to drawing on a flat sheet of paper. Let A be a given point, a its plan on M G, and a' its elevation on any vertical / ! 1/ / ! 'Z plane N G, the ground line being G G. If from a and a' perpendiculars a B, a' B are drawn to the ground line, it is obvious that they will meet that line in the same point B, so that a A a' B forms a rectangular parallelogram ; and, therefore, A a =r a' B, A a' r= « B. Imagine now the vertical plane turned about the ground line G G as an axis, in the direction N N', until it coincides with plane M G'. The line a' B remains at right angle to G G', and when a has come to a", the line a" B is still perpendicular to G G', and equal to a' B, or a A, the height of point A above the horizontal plane. Taking the surface of our paper for a horizontal plane, and supposing the vertical plane turned down till it coincides with it, we are enabled to construct both plan and elevation on our sheet. LctG G'be our ground line or intersection of the vertical and horizontal planes, and a the plan of a point : the point itself lies somewhere in a vertical line, through a, and its elevation must be somewhere on the perpendicular drawn from a to the ground line, at a distance firom B equal to its height above its plan. If, then, a and a are the plan and elevation of a given point, we know that it lies vei'tically above a at a distance equal to B a'. PROJECTIONS. 57 Acain, if ab and a' h' be tlie plan and elevation of a straight lino A B, we sec that tlie extremity A lies vertically above a, at a distance m a', and that B is vertically above h, at a distance n b', so that B is higher than A byn b'—m a' = b', whilst a J is the distance from A to B, measured horizontally. Apian, therefore, gives us the horizontal distances, and an elevation the vertical distances between any two points ; hence, we can fully fix the position of points, and consequently of lines and sm-faces. We have said that the plan is invariably the same, whatever be the position of the horizontal plane of projection: in the example of a parapet, imagine now the work resting on the horizontal plane itself, the plan is not altered, and the elevations remain the same as they were; but their bottom lines coincide with the ground lines. 58 PROJECTIONS. The vertical planes being now turned until they coincide witli the horizontal one, we have the elevations and plan represented on the same sheet, the ground lines indicating the positions of tlie vertical planes, and the elevation of any point being still on tlie perjjendicular, drawn from its plan to the ground line. (67.) These principles once understood, we can proceed with the drawing of a few elementary examples of Fortification. Let us, for the first step, draw the plan of a parapet 12 feet thick, 8 feet high, and 20 yards long. In order to ascertain the true horizontal distance between every line of this parapet, let us draw M N to represent the level of the ground ; and erect a per- pendicular A B =: 8 feet, take A C:=12 feet, draw the perpendicular C D = A B — ^ = 6 feet, and join B D ; take C N= C D and join D N ; parallel to M N and 4-25 feet below B, draw a lino L O; from O to E carry the third of 4-25= 1-4 and join E B ; draw the perpendicular E H, and a parallel L G to it, at a distance of 3 feet or 4 '50, according as the banquette is intended for one rank or two; making GMrr 2 GL = 7-5 and joining ML, we have complotod the profile (51,69), and we have in M G, GN, HA, AC, CN, the horizontal distances between each line of our Fortification. If now we make A A' =20 yaixls, rcjiresent the sub-t-rcst (or projection of the PROJECTIONS. \ \c y ' a- A (8) J ^ ■ ■ ■■ W H' 1 "\ r\ d a'; / \ ." x' / J- '\ X- line of fire), and draw parallels to it at the respective distances a H= l"4j H G = 3, GM = 7-J, aC = 12, and CN = 6, these lines will be the projections NN' of the foot of the exterior slope, C C of the exterior crest, H H' of the foot of the interior slope, G G' of the top, and M M' of the foot of the slope of banquette. There remains now to be constructed the slopes that limit the parapet at both exti-emities. Suppose that they slant at t : produce A A' of A a =r half the com- mand ■=! 4 feet, and through a draw M N perpendicular to a A; take (jtg = \ the ,_3-75,. height of the banquette : H /t =: G jr ; C c = 4 the height of the exterior crest, and join M -. '+2 s -^ ^ -S -T3 .2^ 1 :§ i c :3 ^^' 8 .^-^l -J .2 1 2 ■3 c a ., ^§ .5 S I ^ <" S 2 " t. m ^^ ^ "^ ^ '^ 2 2 b c»- (M E '^ Or-r^i .^ (^ CHAPTER IV. FIELD WORKS. The profile of a field-work has already been given, and it has been shown that its standard height is 8 feet ; and that the other dimensions are dependent upon the weight of the enemy's metal, and the natui-e of the soil. The outlines of this sort of work vary ad infinitum, but we may classify them under two heads, Isolated works, and combined works or Lines. The former are subdivided into open and enclosed works ; the latter into Continued Lines, and Lines with intervals. SECTION I.— Open Wokks. (75). Under this category wc place all the works opened at the rear or Gorge, and we may reduce them to three types, which are, as it were, the elements of an infinity of others. 1st. The Medan or fleche, formed of two faces salient towards the enemy. 2nd. The Lunette, formed of two faces and two flanks. Fio. 135. ,Yote;_The angle formed by a face and a Hank is calkd shuuliler angk'. OPEN WORKS, 75 3rd. The Tena'dle, formed of two faces, presenting a rc-cutoring angle to the assailant. Fin. 136. Among the many works ilorivcd from these, few have received a special name. The Double Redan. The Tenailk Head. The Queue d'Hironde, or swallow's tail. Fio. 139. The Bonnet de Pretre. All these may be somewhat modified, especially to obtain flanking fire, but they still retain their names ; thus — A, A, X, are still called redans 76 OPEN WORKS. Tlio name of Ilornworks, or Bastion-head, applies in general to all works com- posed of abastioned front (78) and two faces. Fig. 142 n n That of Crown Works to open works containing two or more Ijastioncd fronts. Fio. 143. When any one of these works is employed to defend a bridge, it is called a Bridge-head — Tete-de-Pont in French. A mere inspection of these figures, shows the defects of these outlines when employed by themselves. Thus the Redan and Lunette have no flank defence, and the ground before the salients is deprived of fire. The Tenaille has flanking fire, but its ditch contains a dead angle. We may here observe, that although these works have by tliemselves but a weak outline, they are, nevertheless, capable of making a most vigorous resistance when flanked by others in the rear ; the inconveniences we have alluded to are besides, as we shall hereafter see, obviated by accessory means, such as artillery, obstacles, &c. Of the tracing of these works on pai)er, we say nothing, because their outline varies indefinitely, and the conditions (57, 58), relating to the opening of the salient, and re-entering angles, and to the length of the lines of defence, are the only ones to be obsei^ed. r J 1. hi SECTION II.— Enclosed WoEKs. (76). Here, again, we have three different types— the Redoubt, the Star-fort for fortlet, and the Fort. A Redoubt is an enclosed work having no re-entering angle, and is formed of four, five, or si^^-^acos, but generally cif I'our. it may even be circular. ^ - t f -~ ? X ; l^' y) z STAR-FORT^ FlO. 144. Ol Fio. 145. Fio. 146. / X ii,H □ ooo The circular redoubt is rarely employed, as it is more difficult to throw up than the others ; tho square is most generally preferred. The defects of the redoubt are obvious, viz., imdefendcd angles before each salient, and miflanked ditches. In order to remedy the want of fire at the salients, it has been proposed to trace them "en cremaillero," but this plan has not been found expedient in practice. (77). A Star-fort presents a series of salient and re-entering angles ; tho number of salients may be four, five, six, eight, &c. It is easy to perceive that the Star-forts of four and five salients must be cntii-ely laid aside. Their outline is opposed to principle 58, since the condition of making the salients greater than 60°, gives re-entering angles of 150° and 132°. The Star-fort of six salients is the first, the outline of which is superior to that of a redoubt, its angle of defence being precisely equal to 120° ; yet it should not be employed indiscriminately, because the enemy advancing on the capital is only exposed to oblique fire (fig. 150). In the heptagonal (fig. 151) and octagonal (fig. 152) Star-forts, the capitals receive direct fire, which renders these two tracings preferable. Star-forts of a greater number of salients are not employed in the field, because their garrison would be sufficiently sti'ong to defend a fort. The Star-fort is not so much preferable to the redoubt as would be imagined at first sight, because the greater part of the ditch is dead, the enclosed space is small for the long extent of their parapet, and their faces arc exposed to enfilade. Despite the defects of these enclosed works, star-forts and redoubts are frequently constructed ; and militai-y liistoiy gives us instances of the great value of works having of themselves but a weak outline. Thus, at Montenotte, in 1796, a redoubt, garrisoned with 1500 French Grenadiers, resisted successfully during a day and a night the repeated attacks of 12,000 Austrians. The redoubt of the Stamboul gate at Silisti-ia, in 1854, stood the continuous attacks of the Russians. The redoubts established in 1855, at Kars, by Colonel Lake, owing to their skilful disposition and mutual flanking, resisted for several months the eftbrts of the Russians. A few words may bo said on the tracing of these forts : — 1. To trace on paper a Star-fort of six salients, describe an equilateral triangle, trisect each side, and on each centre portion describe an equilateral triangle (fig. 153). 2. To trace an eight salients' Star-fort, describe a square, trisect each side, and repeat the above construction (fig. 154). 3. This tracing is somewhat improved by replacing the angle of the square by an angle of 60°, since the angle of defence is thereby reduced to 105°. It is done by producing the sides ah, a b, till they meet in c, and joining A c, A c, B c, B c, &c. STAR-FORTS. 4. The eiglit salients may be made equal. Describe a circle ; through the centre draw two diameters at right angles, and bisect each right angle. From the extremity B of a diameter, carry the radius B C on the circumference, the line A C will make an angle of 30' with A B ; so will A D. The other salients Fig 156. \}j. k>'' m.ay be traced in the same manner, or the construction may be further simplified by drawing another circumference with radius O H, and joining each salient to Fig. 157. the adjacent points of intersection of this cii O 2, O 3, &c. inifercncc, witii the lines O 1, 80 STAR-FORTS. 5. For the seven salients' fort, describe a circle, draw a radius A B ; from B as centre, and radius A B, describe an arc, intersecting the circumference in a and b, join a b. The line a c is the side of the regular heptagon, which, carried on the circumference, gives the 7 salients. The construction is completed as for the 8 salients' fort. Fig. 157*. The position of the salients may also be found by means of the protractor, by dividmg 360 degrees by 7 or 8, and drawing through the centi'e, as vertex, seven angles of '^-y^, or eight angles of -^^-^^ degrees each. These methods do not enable us to construct a Star-fort, with faces of a given length, except, however, for the cases 1 and 2, in which tlie side of the equilateral triangle, and of the squai'e may at once be taken equal to three times the length of the face. In all other cases, the fort being described of any dimension, join the centre to every angle, and produce the lines thus obtained. In the dircftion of a face take A B equal to the required length, through B draw B B' parallel to O A. If now we draw B'A' parallel to B A, and through A', A'C' parallel to A C, and so on, the starfort B'A'C'D' will have faces of the required length, {see 133). Fig. 158. //, ^^^t*^%r\/^ 81 (78). A fort is the name given to any enclosed work possessing bastions; it may be square or pentagonal. Kio. i.-ig. ^ Of hastions. — The serious inconvenience of dead angles has rendoi-cd it advisable to adopt a combination of such a kind that in no part of the ditch should a man be sheltered from the fire of the defenders. The bastioned outline, discovered three hmidred years ago, for permanent works, completely answers this piu-pose, and is advantageously employed in field fortification. Let us suppose that a work of that kind is to be constructed to defend a position, and let us take the case of a squai'e fort. The lines A B, B D, D C, C A, wliich vary from 200 to 300 yards in lengtii, are called fronts, and for each of tliem the construction is the same. ■''/| On the middle of the line A B, a perpendicular C D, called the perpendicular of the front, is drawn ; and towards the interior, a length C D is taken, equal jth of the front. Join A D and B D ; on these two lines measure the 82 BASTIONS. distances B E and A H, each equal to J rd of the front ; from H draw H K perpendicular to K B, and fi'om E, E M perpendicular to M A. Join K M, and A H K ]\I E B will be the outline of the bastioned front, which consists of t^vo half bastions and a curtain K M. The same construction being repeated on each front, a bastion K H A O L is obtained.* The lines H K, EM are called flanks; A II, BE, faces; KL, the gorge of the bastion ; A T, the capital ; K R, the demi-gorge ; A M, B Iv, the lines of defence. The angles H A O, E B N, are the salient or flanked angles ; H K B, E M A, the angles of defence ; H K M, E M K, the angles of curtain, or of the flank ; A H K, M E B the slioidder angles; and C A D, C B D the diminished angles. On inspecting this outline, it will be perceived that at whatever ]Kiint the enemy presents himself, he is exposed to cross fire in several directions ; and that if D M is greater than 30 yards, there is no longer a dead angle. The length of the perpendicular, fixed at ^th of the front for the square, is made |th for the pentagon, and J^th for figures of a greater numl)er of sides. In hornworks and crownworks the same construction is adopted, but the perpendicular which has been fixed for enclosed works so as to give more than 60° to their salients, may now vary from ith to T^th. Many engineers object to the employment of bastioned fronts in the field, because the defenders on the flanks are liable to flre at each other; but there is no doubt that for an important position the bastioned tracing is the best. In order to give more fire on the salients, the curtain has occasionally been broken, Fig. 162. Fig. 163. as in these diagrams ; but it becomes exposed to enfilade, of several other tracings, such as the accompanying. When the ditch of a bastioned front is excavated parallel to the faces, flanks, * This word comes from the Italian ' bastido,' a tower ; bastions made of earth were invented to replace in permanent fortification the tower that flanked the walls of a town, after the discoveiy of gunpowder and the use of artillery. BASTIONS. 83 and curtain, one of the great advantagos obtained from (his tracing is lost, as may be seen by making a profile on h c The shot grazing the counterscarp in a does not reach the bottom of the ditch until c, and with the ordinary relief, a c measui-es 70 yards. It becomes necessary, then, to excavate the ditch, as below, which entails great labour. When time is of importance, the amount of excavation may be reduced by Fio. 167. 84 BASTIONS. cutting a ramp in the prolongation of the escarps and counterscarps of the faces of the bastions, but the ditch of the flanks is still without defence. To avoid this defect, the whole mass of earth before the em-tain may be cut into a glacis, the (plane) surface of which passes through the crest A B of the flank, and a line a b, situated 2 feet above the bottom of the ditch. Fio. 168. Another modification of the original tracing, which has been made for the jiurpose of diminishing the deblais, consists in bringing the original curtain A B forward to C D to the distance ??i'«' = mn = thickness of the parapet, because the part C A of the flank does not contribute to the defence of the ditch ; but it is not an improvement as far as the outline is concerned. We may also state that if the flanks are merely intended to flank the ditch, a perpendicular = .Jj is sufficient for that purpose, but the tracing becomes for inferior to the original one. Sometimes a small redan is placed before the curtain, to give flanking fire on Fig. 170. BLOCK-HOUSES. tlie capitals of the bastions, but its small saliency does not prevent the enemy from attacking the bastions. (79.) The demi-bastioned fort has sometimes been employed. It is described on a square A B C D. Trisect a side A B in G and E. Produce the adjacent side, making B L = B E, join L A, and erect E H peqiendicular to A B, and Fio. 171 A \ s s B . repeat the same construction on every side. This is a bad work, having as many dead angles as half bastions. t''^''^{80.) Among enclosed works we may place block-houses; these are em- ployed in woody and mountainous coimtries where timber abounds, and where artillery is not likely to attack them. Their outline varies; the square and the o cross being the most general forms. The walls are formed of logs of wood from 9 to 12 inches square, bui'ied 3 feet, connected to sills and cap-sills, the latter consolidated by girders. The interior should be 20 feet wide, and 9 high in the clear. Loopholes are pierced 3 feet apart ; and a banquette, serving as a 73. m BLOCK-HOUSES. cauipbed, allows the men to fire through them. A parapet of earth and a ditch prevent the access of the enemy. When ai-tillery can be brought against these works, their wall is made of two rows of logs, the sj:)ace between the timljer being filled up with earth well rammed in. The profile of their walls varies nmch. The roof is covered with earth 3 feet tliick to avoid fire, and render it bomb- proof, and is sometimes furnished with a banquette. Sometimes the blockhouse has two stories, (See fig. 175) and machicoulis are pierced in the projecting floor to defend the foot of the lower stoiy. The men enter the upper story by means of a ladder. These works make good defensive bai'racks in a hostile country. Blockhouses were erected in 1849, in the bastions of Vienna, commanding the principal streets, as a defence against future internal enemies hi the Austrian -- capital. -) J \ SECTION III.— Continued Lines. Lines is the name given to the intrencliments constructed to fortify the position of an army, or to connect important forts or redoubts. According to their object, tiiey are called Intrenched Positions, Intrenched Camps, Lines of Circumvallatioti, Lines of Contramdlation ; but tiio two last are obsolete. (199.) With regard to their arrangement, they either cover the ground without inter- i-uption, or are composed of works combined for a common defence ; in the first case they are called Continued Lines, in the latter, Lines with Intervals. (8L) Continued Lines are generally to be avoided, on account of the amount of labour they require, which bears no proportion to their value ; in fact, the defenders may expect an attack on every point and pi-cparo for it, whether real or false, and when once the lino is forced at a point, it is altogether lost. Yet, there are circumstances, when they are advantageously employed, as, for instance, to co\er a besieging army. Their outline varies indefinitely. The cliief sorts may, however, come under the following heads : — The Tenaille Lines. The Lines of Vauban or Redan Lines, with small or large Redans. Fig. 177. Continued Redan Lines. INDENTED LINES. Indented Lines. Bastioned Lines. (82.^ In these woi-ks we call line of front, the line that joins all the salients, and zone of defence, the gi'ound situated before them as far as a lino parallel to tlie front, and on which the enemy is within range of musketiy, the fire being sup- posed to be perpendicular to the crest of the parapet. The deeper this zone the better, since the enemy remains exposed during a longer time. jT"' A discussion on some of these continued lines will give an idea of the principles ' on which they should be traced. (83.) Tenaille lines : — As their salient and re-entering angles are necessarily equal, the opening of these angles can only vary between 90° and 120°. The minimum of the faces is already known as 30 yards (59). To find the maximum distance between the salients, the following method will apply to any sort of tenaille. A salient BAD being traced in direction, together with the line of front A M, and a line A Q being 'drawn perpendicular to the face A D, to represent the direction of the last shot, it is cleai- that the capital of the next salient should cut this line within range. Therefore, on A Q, measure A O equal to the range given, tlu-ough O draw O K parallel to the capital A H, and the point A' where this line intersects the front, gives the position of the next salient required. Sup- posing the range to be 300 yards, the following residts may be noticed. Faces. Dist.ince between salients. Depth of zone of defence. Perimeter for 1000 yards. 150 yards. 212 yards.. 212 yards... 1414 125 „ . 192 „ .. 229 „ ... 1305 . 104 „ . 171 „ .. 245 „ ... 1220 86 „ . 150 „ .. 259 „ ... • 1154 90° 100° 110° 120° The inspection of this table shows that it is advantageous to open the angles to the maximum of 120°, since the labour is diminished whilst the depth of the zone of defence is increased. Besides, the enemy cannot enfilade them so easily, being obliged to come nearer the front to clo so. In general, the tenaille ti-aeo has the drawback of presenting many points of ^^l attack, of requiring much labour, and of being exposed to enfilade. /A-^- (84.) Lines of Vaulan or redan lines : — Vauban usually constructed two sorts . /^ of lines, those with gi-eat redans and those with small redans. The great redans / had 80 yards gorge and 55 yards capital, the small ones 60 yards gorge and 44 yards capital. In both eases the salients were placed 240 yards apai't. This tracing was bad, because the angles of defence were greater than 120°, and the undefended angles were not flanked within proper range for the old musket, 90 LINES OF VAUBAN. whilst in front of the ciu'tains where the enemy does not attack, the fire crossed in three du-ections. The defect of the angles is now remedied, by making the redans equilateral ti'iangles of 60 yards face. The distance of 240 yards, would not be too much at present. However, the range being given, the maximum distance between two salients is found as for the teuaille by taking A E, perpendicular to A C, and equal to the range. A further improvement may be made in this maximum line, by lengthening the faces of the redans, till they meet the perpendicular B H, drawn upon their direction fi-om the exterior crest of the adjacent salient. The minimum distance is obtained by the condition, that the last shot fi-om the face at C, shall graze the salient of the pai'apet in M. In this case the distance is 130 yards. A Supposing the range 300 yards, the maxiuumi distance between the salients is INDENTED LINES. yi 260 yards. The jierimeter of the parapet for 1000 yards uf front, is equal to 1230 yards for the line maximum, 1500 yards for the same modified, and 1615 yards for the line minimum. Tlie depth of the zone of defence is 248 yai'ds. It has been proposed to alter the tracing of Vauban in a dift'crcnt maimer by breaking the curtain, but it is evident that it gives a greater number of points of attack, and that tiie branches that replace the curtain become exposed to enfilade. Anotlicr form of the redan line, is the following, which is sometimes called the caponier tracing. (85.) Indented lines. — Two sorts have been employed, respectively called great and small "cremaill^re." The line of front was divided into equal parts of 120 or 90 yards, and perpendiculai-s of 40 or 30 yards drawn through the points of division. By tracing the diagonals of the rectangles thus obtained, either to the right or left, and tkopping perpendiculars from the point of division upon them, a line was obtained which easily adapted itself to all varieties of ground. These lines are more advantageously employed along the side of hills, as the short branches by an increase of command, admit of an easy defilade (Chapter VII.) The long branches, owing to theii' inclination to the fi-ont, render the enfilade difficult, as the batteries of ricochet must be established rather near the front. In taking the range into accoimt, and adopting 30 yards for the minimum flank, the greatest distance between two salients is found by the condition that the shot from one salient shall reach the capitid of the next. With a range of 300 92 INDENTED LINES. yards, it is evident that the long branch measures 270 yards, and that the sides of the rectangle are respectively 271 yards, and 31 yards. In giving any dimension to the flank, the range must always be equal to the sum of the short and long branches. In the example selected, the zone of defence measures 284 yards, and the perimeter 1265 yards. To generalize the tracing of this sort of line, let us calculate the dimensions of a cremaillere, in wliich the shot from one salient, will reach the capital of the third salient, the range being 300 yards. Giving 30 yards to the flank, the in- spection of the figure shows that the range must be equal to 3 times the sum of the long and short branches ; hence 300 =3x30 + 3 times long branch, and long branch rr 70 yards. Fin ISq •< To protect these lines from enfilade, the original ti-aciug is sometimes altered as in the annexed diagram, where the long faces are directed to a point on wlxich it is supposed the enemy cannot establish himself. BASTIONED LINES. (86.) Tn Bastioned Lines, the front to bo fortififd is dividod into partial fronts of 200 yards, and on each of them the construction of No. 78 is rc|>eated. The tracing that follows has been proposed to diminish the nimaber of the salients of attack, C E is taken equal to A D, and the flanks are traced perpendicular to tlie lines of defence. The ditch, however, is not well flanked, owing to the small dimensions of the curtain. SECTION IV.— Lines with Inteevaxs. ^^ ^^.i/ftsA/- (87.) These are formed of detached works, placed at such intervals as to derive protection from one another, and so as to cross their fire on the intervening space. Different outlines may be selected, two or three rows of lunettes, or two or three rows of redoubts. <>. ■O o o Such lines can bo more easily adapted to the ground, and occasion less labour; they permit the defenders to move rapidly and in force on the intervals to repel 94 LINE WITH INTERV.^.LS. tlie attack, and assume the oflfensive when the opportunity presents itself; an immense advantage over Continued Lines, where the defensive attitude is compulsory. During the seventeenth and even the eighteenth century, continued lines were frequently employed to cover an army engaged in besieging a fortress, or to defend a position ; but experience has made us wiser: we no longer employ them in a siege, and we have recourse to lines with intervals whenever we have to defend a position of some extent. At Arras, in 1634, Turenne made three false attacks on the lines constructed by Conde and the Archduke Leopold, and succeeded in forcing them. In 1656, at Valenciennes, the lines of Turenne were also forced by Conde. In 1706, at Turin, Prince Eugene defeated Marsin, who awaited him behind his linos. In 1793, the Prince of Cobourg, commanding the Austi-ian forces (60,000 men), was attacked in his lines at Wattignies, by General Jourdan, at the head of 40,000 French troops, and was compelled to raise the blockade of Maubeuge. It was during the Seven Years' War that the Prussians and Austrians had recourse to powerful combinations of lines with intei-vals. The most remai'kable were those of the King of Prussia, near Jauernig ; those of H.R.H. Prince Henry, near Liebenthal, in 1759; those at Colberg, in 1761 ; and those of the Austrians at Dijipoldiswalde, in 1759; at Boxdorff, in 1761, and upon the high Eulenge- birge, in 1762. In the Peninsular war the most celebrated were those constructed at Ton-es Vedras, by the Duke of Wellington, in 1810. (88). Lines with Intervals. — The following formiila for tracing a line with in- tervals may be taken as a fair standard. Divide the line of front into parts of 300 yards, A B, B C. Bisect them in D, E, and through these points draw perpendicular DP, E Q, measimng 120 yards. Join A P, B P, B Q, C Q, and on these lines take 40 yards on P/, Q/, to obtain the faces of the lunettes of the second row. If the points A, B, C, &c. are respectively joined to the extremities f,f, of these faces we obtain the direction of the faces of the lunettes of the first row, which can also be made 40 yards long. This tracing will protect the second line against enfilade, and tlie angle of defence will measiu-e 90°. The flanks are made 20 yards long, so as to receive four guns. To trace them, from the shoulder angles of the lunettes as centi-es, describe circles of 20 yai'ds radii. By di'awing tangents wi F, nf, &c., to these circles tlu'ough the salient of the crest of the parapet of the first lunettes, the point of contact gives a second point of the flank, which will thei-efore make an angle of defence = 90°. 95 An additional row of works can be obtained by producing tlie faces P/, Q/, of tlio hmcttes of the second line, measuring 20 or 30 yards on »-M, and joining Q M and P M. These redans are not exposed to enfilade. A foitrth line of works would be superfluous, as the force which would allow the three rows to be carried could not be expected to defend a fourth. The defensive properties of this line are gi'cat, for the assailant must carry three works of the first row, two of the second, and one of the tliird, altogether six works before an opening can be made. The amount of labour for 1000 yards is only 1000 yards of parapet. It is usual in all lines with intervals to construct the ditches of the works of the first and second rows, parallel to the faces and slanting into a ramp, so as to expose it entirely to the fire of the work in rear. (89.) To complete the nomenclature of field-works, there remains only to mention the reduits, or interior retrenchments. They are woi-ks of any out- line thrown up in the interior of a large work (fig. 196), and ovei-looking the sur- 96 rounding terroplein, either to seno as a place of refuge to the garrison and facilitate its reti-eat, or to keep possession of tlie principal work with a small force. Such reduits ai'c difficult to establish in the field, inasmuch as they imply a work of great magnitude, and, unless the groiind be very imeven, they would be too much exposed to the plunging fire of the enemy mounted on the parapets of the intrench- ment. Besides, if the garrison perform its duty, it will remain on the banquettes to the last moment, and the enemy would enter into the reduit pele-m^le with the defenders. If, however, this interior retrenchment be placed in some re-entering pai't, where the defenders can retire under the protection of its fire, it may become most useful. When a gamson, after having repulsed several assaults, has been reduced to a small number, and has become too weak to hope for a vigorous resistance, a reduit can then serve as a refuge and a citadel. A circular redoubt, although deficient in outline on account of its diverging fire, has sometimes been found an excellent reduit for a system of opened works. A block-house may serve as a defensive baiTack and interior intrenchment, to guard a larger work. In mountainous countries, among hostile populations, such block-houses surrounded by field-works, which the garrison can defend if neces- sary, have been found most advantageous to occupy the chief passes with, and to protect the resting-places of convoys with. It is chiefly in tlie works destined to cover bridges (183) (tetcs-de-pont) that interior retrenchments are met with in the field. They are, in fact, indispensable. When the army retreats, it first collects behind the principal work, whose artillery and musketry delay the advance of the foe, and give time to the troops to cross the bridges. As soon as the principal work has fulfilled that purpose, the reduit continues to keep the enemy in check in the terreplein in front, covering the last retreating body ; and, as soon as the bridges have been destroyed, its small garrison hastily retires on rafts or in boats kept ready for that purpose. The tete- de-pont of Cassel, constructed by the French in 1792, was intended to allow space for 20,000 men to fight, and yet it could be defended by 3000 men only. The works throwTQ up at Nordheim, on the Rhine, in 1744, by the Prince of Conti wliile retreating, afford an example of the most judicious employment of the tetes-de-pont with reduits. The tetcs-de-pont erected on the Vistula in 1806 and 1807, those on the Danube in 1809, that at Dresden in 1813, that of Praga, on the Vistula at Varsovia, &c., present similar dispositions. d^.-^-^T/' 6 ^, t- I- CHAPTER V. .iSr SELECTION OF FIELD WOEKS. ^ ^ ^- } q 6 The ground is th^ first element to be considered before selecting a particular outline, but it is not the only one. We must also bear in mind the end for wliich the work is designed, and the force of the ganison destined for its defence. Again, tho amoiuit of labour, and the time required to throw up the work, may fui'ther induce us to modify this outline. (90). With regard to the ground, and tho puqjose of tho work, no absolute rule can be laid down ; here all is left to the ingenuity of the officer, and it should never be forgotten that it is not by difficult and complicated tracings that skill is displayed. If a bridge thrown across a river is to be defended by a work, the figure shows that a redan (fig. 199) would not answer the piu'posc if the river runs in a straight line, the assailant being in fact unexposed in his approach on the ground A and B ; this outline would, on the contrary, be good when the river presents sinuosities : the lunette should be preferred on the former supposition (fig. 200). FiQ. 200. GROUND. 00 If a marsh or ground impassable to the enemy is in the vicinity of a posi- tion, it would be absurd to place a face |>arallel to the obstacle, since its fire would 1)0 lost. On the contrary, in directing a salient towards it, we at once obviate the disadvantage of the want of fire on the capital (fig. 201). o V/ If a work must be thrown up close to a commanding height, the outlines 1, 2, .3, would give faces exposed to enfilade and reverse fire, and therefore the outline 4 should bo preferred (fig. 202). If the work is to be constructed in a valley between two commanding heights, outluie 1 would again be absui'd, so would be any other than figure 2 (fig. 203). ^5T%. Again, the redoubt 1 has all its faces exposed to enfilade and reverse fire, while redoubt 2 has better conditions (fig. 204). -^ Examples of this kind could hr^ multiplied ad infinitum, but a perusal of former campaigns is the best exercise tliat can be recommended to an officer desirous, in time of peace, of acquiring information, if not experience, on this inijKJrtant subject. In general, none but good positions should be fortified, and the command should, as much as possible, be obtained fi-om the ground itself rather than from high parapets. In hilly regions, the summits ai'e good points to occujn-, because a command of 5 to 6 feet is sufficient for cover ; but in general the crests are not sharply defined, and the works must be constructed on the side of tlic hill, in order that the whole slope may bo seen. Shoidd the crests have salient ponits, of com'se these should be preferred. (91). As for the object in view, it may be said that, in general, redans are employed to cover the front of the enemy, to defend a road, a bridge, a dam, a gate, &c., when the gorge is not exposed to be turned. A lunette will answer the same pm-pose when the flanks can defend some parts of the grounds not seen from the faces. Double redans, queues d'ldronde, bonnets de pretre are preferable when the extent of gi-ound is greater. Horn tvorks and crown works scarcely belong to field fortification : they serve for the defence of several bridges, as reduits for intrenched camps, &c. Of the inclosed works, redoubts are constructed to secure an advanced post, to occupy a defile, to support the wings of an army, to flank lines of intrenchments, to defend an inundation, covering the front of a position exposed to bo turned, &c. Stai--forts -AuA forts have a similar purpose when thegai-rison is more numerous, and when the position must bo occupied for a longer time. When the operations of an army render it necessary that a position should be fortified and occupied for the whole campaign, the works assume more impor- tance, and may consist of forts having .'> or 6 bastioned fronts. Such a fort is GAKKISON. Ktl (■;illecl a "place du moment." An open town in whicli magazines, liospitals. itc, arc cst:il)lisiied, is frequently ti-ansf'ormcd into a field fortress, and it should possess such outline and profile, as to oblige the enemy to make a regular °'°"" '^-'^^ f52). To calculate tlie garrison of a work- already constructed, wo measure the perimeter of the parapet, and allow one or two men per yard ; but with such a force the defence will be slack, and it is better to allow two men per yard, plus :i reserve of one-third the whole garrison, i. e., a man per foot. If a lunette has 90 yai'ds of parapet, the garrison will muster 270 men, of whom 180 are stationed on the banquette, and 90 are kept as a reserve. Slioukl two ranks and file be deemed necessary, the garrison Avould Ijc 540 men, 360 on the banquette, 180 as resen^e ; but the former number is quite sutKciont for a \igorous resistance. Let it be understood that in measuring the perimeter, we do not include the part occupied by guns. • When the garrison is given, and the outline of the work is optional, we act on the same principle. Let us suppose that we have to tln'ow up an open work for 480 men. Of these, 320 will be on the banquette, and 1 60 on reserve ; at the rate of two men per yard the perimeter of the parapet is 160 yards. This length is tiien devised into the outline that will best suit the ground. In this example, a double redan will be preferable to a redan of 80 yards faces (fig. 205). FlO. 205. In this calculation, allowance should be made for guns, at the rate of 15 feet each, and 40 feet for those in capital. When the work is an enclosed one, a new item must be taken into consider- ation, viz., the area of the terreplein, every man requiring 15 square feet to bivouack. In star forts and bastion forts there is always moi'e interior space enclosed than is required for the garrison, but in squai-e redoubts the case is different. The distance between the subcrest and the terreplein being 12 feet, it is clear that tliore would be no terreplein when the side of the redoubt is equal to, or less than 24 feet, or than 27 feet when the banquette must be 4 feet 6 inches wide. Fio. 206. 12 f. "72 f." A few examples will illustrate the mai'(>h to folic 102 GARRISON. Let us calculate the dimensions of a square redouljt for 350 men, of Avhom any number may act as reserve. Each man requii-ing 15 squai'e foet, the area of the terreplein should measm-e 15 X 350 = 5250 square feet. The mass of earth (traverse) usually erected to Fio. 207. cover the passage, for the ingress and egress of the garrison, absorbs 1 000 feet, so that the whole area should measure 5250+ 1000 or 6250 square feet. The square root of 6250, i.e. 79, gives the side of tlie terreplein, and adding 24 to it, we find the side of the redoubt equal to 103 feet. Shotdd the redoubt be intended to contain guns, we allow 500 square feet for each piece, which includes room for gunners and ammunition, and 500 square feet extra for every barbette (96). The side of a redoubt intended for 300 men with two guns en barbette, and tlu-ee in embrasures must have a terrcj)lein of area=: 300 x 15 :z: 4500 for men, + 1000 for traverse, + 500 x 5 = 2500 for guns, + 500 x 2 = 1000 for the barbette; altogether 9000 square feet. The side of the terreplein will therefore be 94 feet, and that of the redoubt 118 feet. This calculation is made whenever the garrison has to occupy the redoubt for a considerable time, and must therefore bivouack in it ; but when it is thrown up for an occupation of a few hours only, the dimension of the terreplein is altogether neglected, and we calculate the side of the redoubt by the general method. Let us, for instance, suppose that a redoubt is to be constructed for 240 men, with 3 gims along the parapet, and one in capital. If nothing is said of the number of men allowed for every lineal yard of parapet, we adopt the ordinary rate of 2 men and a reserve. Of these 240 men, f or 160 will line the parapet, the remainder, 80, acting as reserve. The 160 men require -L^zz 80 yards of parapet, or 240 feet; the guns must have 15 x 3 + 40 or 85 feet. Thus the perimeter of the redoubt measures 240 + 85 or 325 feet, the side therefore = .a^Az=8i feet. It may readily be seen that such a redoubt cannot give accommodation for its garrison on the terreplein, since its ai-ea measures only (81—24)- ^ 3249 square feet, whilst the men, traverse, and giuis require 7100. When the redoubt is to be defended by a certain number of men per lineal yard of parapet, and must at tlie same time accommodate its garrison on the terreplein, it is easily seen that the problem is not indeterminate, but that there is a minimum side with a corresponding minimum garrison, mider which the two conditions cannot be made to agree. We must have recourse to algebra to solve tills problem. DIMENSIONS. 103 Let us suppose that such a redoubt must bo constructed with one man per lineal yard of parapet. Let N represent the garrison and X the side of the redoubt in feet. The garrison N zz -^ , and as every man requires 15 square feet, and the traverse 1000, the teiTeplein (X-24)- = 15 N + 1000. In solving the equations, we find X =: 73, N := 97. Hence, no redoubt with a face smaller than 73 feet can be made which will hold its garrison, and be defended by one man per yard ; but any redoubt larger will do it, since the ai'ea of the terreplein inci'eases more rapidly than tJie perimeter. A similar minimum may bo found for a defence by two men per yard ; the 8 X equations would be respectively N :^ -^ ; (X — 24)- ^ 15 N + 1000, giving X = 92, N r= 245. For a defence by two men and a reserve N n: 4 X ; (X —24) - := 15 N + 1000, from which, X = 101, N =404. Should the redoubt contain guns, the method remains the same. To conclude, let us find the smallest redoubt capable of holding two guns in bai'bette in capital, and one in embrasm-e, besides its garrison and reserve. 4X = N + 2x40 + 15=N + 95; (X - 24) = = 15 N + 3x 500 + 2 x 500 + 1000 = 15 N + 3500 The gan-ison ^ 385 men, the side 120 feet. (93.) We have said (92) that star-forts and forts need no such calcidation. Their dimensions are determined on different principles. The question may naturally suggest itself, when should we construct a redoubt, or a star-fort, or a fort ? Supposing the consideration of the ground to be laid aside, we give the preference to the fort, next to the star-fort, since theii" outline is superior to that of a redoubt. If in a star- fort the faces are less than 15 yards, the ditch is entii-ely dead, and the defenders cannot even see the ground immediately in front of the salients ; such works are not so good as redoubts, since they have their defects, and are more exposed to enfilade. But when the faces ai"e above 30 yards, the ditch is seen at the salient by the defenders, and the outline possesses good properties. AVe therefore lay it down that the faces should be at least 30 yards long. The minimum perimeter of a star-fort of six, seven, and eight salients will, therefore, be 360, 420, 480 yards. Hence, when calculating the perimeter of a redoubt for a given garrison, if we find it above 360 yards, we should prefer constructing a star-fort. The maximum of 160 yai'ds has been fixed by some authors for the perimeter of a redoubt, because they consider a star-fort of 15 yai-ds face a possible work, but the generality of engineers allow 360 yards. The perimeter of the smallest square fort, with a front of 200 yards, measures LIMITS OF BASTIONED FRONTS. 920 yards, therefore tlie longest face which should be given to the three star-forts should be ^-^, Vt > tVj or 77, 66, and 57 yards. Above that a square fort can pf coustnicted, ^-H^-l V. 4- ">^- s on the niit 4.) To conclude this Chapter, a few words on the minimum and maximum of bastioned fronts may be added, for the use of more advanced students. One of the great advantages of the bastion trace is, that it has no dead angle ; but we have seen tliat this result is only obtained by excavating the ditch, before the curtain and flanks, as fiir as the counterscarp of the faces. Yet, if the front is less than 200 yai-ds, this advantage no longer exists. To avoid the dead angle, it is necessaiy that the planes of fire of the flanks should meet the bottom of the ditch, precisely in front of the middle of the cur- tain. With a command of 8 feet and a depth of 9 feet for the ditch, the distance M N zr 34 yards. Fig. 208. -^ , -, 3-^' , the With a mean parapet of 12 feet, a berm of 1 foot, and an escarp at distance N Q = 7-83 yards. By means of M N and N Q, the minimum of the front^s calculated. Let A C K L D B, represent the line of fire, e ef the foot of the escai-]i before the curtain : the distance L^ =: Q G = 34 yards, and Q m ^7-83. Through m, draw r n, pai'allel to L P, and through P, draw P q, parallel to D L. The triangle A H P gives : — AH:AP:HP::4: n/T7 : 1 for the square. AH: A P : HP:: 7 : v/^ : 2 „ pentagon. AH : AP : HP :: 3 : v' iT) : 1 „ hexagon. LIMITS OF BASTIONED FRONTS. In Qrm, similar to A H P, the above proportion gives us resjiectivcly in Square. Pentagon. Hexagon. rmzz 1-8 . j-ra ,v>- aiv r<\::v-..i -s piaeevi r.onzonTaiiv ai ii>e crest o: ino est^rp, or rather slifhtlr slant ng dowiiTrards; tbey mast not pro"oot further than the f«x>t of the escarp, in order not to afford cover. Two ribands^ as is seen in the diagram, Irind them tt^:eiher. A glacis nsnally OM»e«ts them. Thev may also be placed on the coonterscarp, bat they ai« then inclined up^srards. ^V^len placed on the escarp they oflfer a serious inc^mvenieiKe. At the storming of Fon Picurina, at Eadajos, in IS 12, the assailants threw their ladd^^ in the manner of bridges on the slanting stakes, — and having passed ov«- them, scaled the parapet by resting their ladders on the step tormed I y these fraises. Two carpenters can make ten palisades per hour, and three men can plant 15 yards in a day. (109). Sfocfcjx;tween WeissenUrg and Lauterburg, was rendered literally 122 CHEVAUX DE PRISE. impenetrable by the French. In 1810, at Torres Veilras, the ravines were secured in the same manner. At Sebastopol, in 1855, the Russians greatly increased the resistance of their works by means of abattis. In putting a village into a state of defence, the trees that border the roads are readily tm-ned into a serious obstacle, by sawing half way tlirough their trimks, and fixing their heads on the gromid. This forms what is called an entanglement. (111). Chevaux de /rise axe not so good, and requu-e more labour; they are fonned of a large joist, 10 or 12 feet long and from 6 to 9 inches square, into the sides of wliich are driven wooden pins, 6 feet long and 1 or 2 inches in diameter. Several are connected together by a chain. Sometimes they are ■l made of iron. They are chiefly employed to close the gorge of a work, to form barricades, or to arrest the inroad of cavalry. (112). Pickets, from 1 to 2 inches in diameter, or thereabout, and from 2 to 3 feet long, and pointed at both ends, affoi-d a good obstacle when placed at small distances from one another. King Henry V. won the battle of Agincourt, in 1415, in consequence of having defended his bowmen watli such pickets. Fio. 254. In the ditch before a caponier, or in front of the counterscai-p, they may become a serious impediment. (113). Crows' feet at the bottom of a ditch full of water, or under an inimda- tion, are used like pickets. They consist of stout nails 6 or 7 inches long, so constructed that one pouit always stands upwards. When scattered on grass MILITARY PITS. 12:i they are a serious hindrance to cavalry. The Romans, by the employment of crows' feet, were enabled to gain a complete victory over the Parthians, whose numerous cavalry would have overpowered their legions, greatly inferior in numbers. Bruce, at Bannockburn, is said to have employed them with advantage. (1 14). Military pits, or Trous de Loup, placed in two or tlu-ee rows in front of the countcrscai-p (at tlie salients, generally), are a formidable defence. Their dcjith may vary fz-om 6 to 8 feet A sharpened palisade is placed in the centre. They may also to bo made 2 feet deep, when there is no time at disposal. On no account should they be 4 or 5 feet deep, because the enemy might turn them into rifle pits. The attack of the French on the Little Redan and on tlie works on Careening Bay, in 1855, failed because the assailing columns were thrown into considerable confusion by rows of trous-de loup, into wliich men stumbled in tlie midst of the darkness caused by dust and smoke. (115). Rifle pits are excavations 3 feet deep and 4 feet wide, affording room for two marksmen : they may be advantageously employed in front of important positions, and in the operations of a siege. (116). Fougasses are mineSj placed at the bottom of smaU shafts sunk in advance of the comiterscarp. They are fired from the interior of the work, by moans of a powder-hose brought along one side of the shaft, and cai-ried through fi inches (fig. 259) below the ground : the exjtlosion breaks the ground, and FOTIGASSES. Fio. 259. throws the assailing columns into conftision. But they are of difficult construc- tion. Their distance from the counterscarp ought to be about t^vice their depth, otherwise the explosion would desti-oy this scarp, the crater of explosion being of a diameter equal to U the depth. (See 250, 258). Shell fougcisses are formed of shells buried imdergromid, either singly or in rows : generally they are placed in double boxes, the fuses passing into y^^ ,gQ a compartment full of powder, with which the hose communicates, rri pn At Badajos the French buried rows or cliaplets of these shells along — ^^ the comiterscarp of the breached faces. A Stone Fougasse is of easier execution. It consists of an excavation 5 or 6 feet deep, the axis of which makes an angle of 45° with the horizon. The powder is placed at the bottom of it, and covered with a strong shield of wood at right angles to the axis, commmilcating with the work by means of a hose. It is then filled up with stones, pebbles, &c., and the upper part covered in with turf. A fougasse 6 yards wide and 5 deep, loaded with 50lbs. of powder and 4 cubic yards of stones, when exploding scatters the material over a squai-e 55 yai'ds wide. At Gibraltar (1782) the defenders had recourse to them frequently. Fougasses are sometimes formed under works for the purpose of destroj-ing them when abandoned. In this case they must be laid 6 or 7 feet below the centre of the parapet before the rampart is built. They may also be laid under the terreplein, as the Russians did at Sebastopol in their redans. (117). Inundations. — When a stream is in the vicinity of a work, an inunda- tion may be formed by constructing dams across the valley; the water thus swells above the banks and overflows the country. To be a serious obstacle, it should be deeper than 5 feet; and when this depth cannot be attained, holes should be excavated here and there, and crows" feet employed, t« render access .liffic.ilt. INUNDATIONS. 120 Tlie up-side of a dam is inclined at •^, the down-side at J or even at ,' , when tliere are 6 feet of water on that side : with a steeper slope, the weight and fric- tion of the liquid would soon injure the work. The top, or cro\vn, is horizontal, and 4 or 5 feet above tlie level of the water up the sti-eam. The thickness at the top is 5 feet, or double that dimension when it is exposed to ai-tillcry. It is advisaljle, in order to protect it against that fire, to trace the dam obliquely to the ground which the enemy can occupy, the upside facing towards that dii'ection, because the down side is not so much covered with water. The material employed for the consti-uction, is extracted from a ditch excavated at about 20 yards, below it, but if the earth foiuid on the spot does not bind well, some clay or puddling must be procured to form the centre of the dam, so as to prevent filtration. The dam is constructed by horizontal layers, an opening being left in the middle to let the stream pass : when both extremities are completed, a belt of sods is formed in front of the opening, and the work is rapidly finished. When sevei'al dams are consti-ucted, the distances at which they arc placed apart, depend upon the inclination of the valley : they are calculated so as to allow a depth of at least 5 feet at the foot of the down side. Thev should be defended bv works or battci-ies in the rear. Waste weirs are ^^ constructed in each dam to let the superfluous water run over into the atljoinhig inundation, but as it would rapidly injure the dam if it were allowed to run over its earthern slopes, the sides and bottoms of the weir are strongly riveted with 12(i INUNDATIONS. fascines or planks. Other fascines are also laid down in tlie bed of the lower inundation to prevent the formation of pits. If the dam serves as a commmiica- tion, a wooden bridge is thrown over the weir. Sluices may also be employed simultaneously with the weirs. (381.) (118). An attempt to form an inundation, should not be made hastily: we must first ascertain whether the soil is suitable, some soils would let all the water soak through in 24 hours ; next, wc must calculate the time necessary to effect the required inundation. Evaporation and filtration both tend to diminish the depth, and when the supply of water is small, they may become prejudicial. The quantity of water V furnished per second by a stream, is found by the formula of Prony. Y z=.l, h, u; m :=: - -07 + n/oo5 + 3233 ^qryft' in which I repx-esents the width of bed, A the mean depth, u the mean velocity per second, i the fall. The volume of water may also be calculated by measuring the section of the bed, and multiplying it by the mean velocity. The mean velocity V is given by V + (W — IV^ the formula of Dubuat. V ^ ~ ' in which V represents, in inches, the velocity at the surface. The evaporation varies from tV to tt inch per day, but in windy days and in summer it is far more. The filtration may be reckoned at 2 inches per 24 hours. Water may also be employed to fill the ditches of field-works ; but this sort of defence fails in winter, and becomes dangerous ; and when a garrison has to remain a long time in an inmidated country, fever does more mischief than the enemy. In tetes-de-pont however, we often make use of it. ^— . ^/ J Y ^ IS CHAPTER VIII. DETEEMINATION OF THE PROFILE OF FIELD WORKS. - ^^ SECTION I.— Defilade. (119). When .a field-work is to be erected in the vicinity of a height that commands it within the range of musketry, it becomes necessary to conceal its interior from the plunging fire of the enemy. This is done sometimes by modify- ing the outline ; otherwise, we ari-ive at the solution of the question by altering the relief — either raising the parapet or depressing the terreplein — an operation called Defilade. This is a very important pi'oblem, inasmuch as the veiy purpose for which the fortification is made is not obtained if the men ai'e not covered : they must move without being seen on the banquette and the terreplein. In open works, the gorge is the limit to which the defilade must cover the gan-ison ; and in lines, this limit must extend as far as 20 yards in rear of the innermost tracing, because much space is required for the lai'go bodies generally occupying these works. Let us suppose H a height, within reach of musketry of a lunette, G a point of the gorge, and A the salient. By the line of gorge and the commanding point O, we imagine a plane called the Plane of Site, the trace of which is here represented by the line OG. Parallel to and 8 feet above it, another plane, the trace of which is here represented by BC, is called the Plane of Defilade. 128 DEFILADE. If the crests of the work are kept in this plane, the terreplein and the gorge will evidently be covered. The increase of relief must not exceed 4 feet, otherwise another position or another outline must be selected for the intrcnchment. The defilade can also be effected by sinking the ten-eplein and keeping it parallel to the plane of defilade. Fig. 265. In such case the ditch becomes smaller, or a glacis must be constructed to got rid of the surplus of earth. The first method is preferred in the field, when time is a matter of importance. If the work is to be defiladed from artillery instead of musketry, the plane of defilade is 4 feet only above the plane of site. 1000 yards is generally the greatest distance from which we defilade a work from artillery fire. The great difficulty of defilade consists in the proper selection of the plane of site ; this plane should pass over all the commanding ground, therefore it is not the highest point, but that point whose apparent elevation is the greatest, which the plane of site should pass through. (120). When the commanding ground is in front of an open work, there is no difficulty in defilading its terreplein, or even a larger zone of ground in its rear, as is the case with tetes-de-pont, when the bridge or dam they protect must be concealed from direct view. But when the work is enclosed, the problem is more difficult. It is clear that in raising the part of pai-apet nearest to the height, the men mounted on its banquette become exposed to the reverse fire directed over that part of parapet which is more remote from the commanding ground. Thus the men standing on the banquette a, are exposed to the fire du'ected from R, and the more so in proportion as the parapet is made higher. In this case, the most advantageous that may occur for an enclosed work, the terreplein is defiladed, yet it is necessary to erect a traverse or parados, to cover the men from Fio. 267. DEFILADE. 129 the reverse fire direeted from R, (C and R ai-e supposed to be at tlie liniil from which we must defilade,) to 8 feet above the banquette a. (134.) This parados would not always be sufficient, as in the following case wliere the men on banquette a, being covered from reverse fire from R, those on banquette b, are exposed to reverse fire from c. Here the parados must be raised up to m. Fio. 268. Hence, to defilade an enclosed work, it is indispensable to construct a traverse or parados across its terreplein, when the work has the commanding height in front, or is on the side of a hill. B O (121). Should the commanding height be situated on the right or left of open works (fig, 270), a similar disadvantage attends them, and a pai-ados is also necessary; and if there is a height on both sides as well (fig. 271), a traverse must bo erected, which will cover both banquettes. A % In the case of an enclosed work, it is a matter of the utmost difficulty, and whenever the commanding ground is on the front and on the side at the same -ffl time, two traverses across the terreplein must be constructed. Should it be commanded in all directions, it would no longer be possible to defilade it. 130 DEFILADE. (122). When the ground only rises slightly in front of a salient, a mere increase of relief, 2 or 3 feet,'on a length from 4 to 5 feet of the parapet, called Fig. 273. a bonnet, is sufficient to prevent the enfilade. Bonnets are sometimes employed along faces, between guns firing en barbette. Traverses with fascine or gabion revctment.s fulfil the same purpose. Although these parados gi-eatly increase the labom-, and render the communication difficult, still, when time is abundant, they are most valuable. Passages are cut through tliem to enable the garrison to pass freely from one part to another, and they form a good shelter for powder magazines. Their profile varies : the thickness at the top should be 3 feet to resist musketiy, or from 6 to 9 to resist artillery. This top is cither horizontal or inclined in a ridge to carry off water. The slopes on both sides are at -f. When there is not sufficient room in the terrcplein for a traverse of this kind, a mask of timber and earth may be substituted for it. J To protect the banquette ft-om ricochet fire, small traverses of this description m DKBLAI AND REMBLAI. 131 are sometimes constructed. As a drawing exercise, we give tlie jilans of two jKirados, one along a face (fig. 277), the otiier at a .salient (fig. 278); their top is horizontal, and their slopes at -f. rio. 277. Kio. 278. We should avoid the necessity of having to defilade fieldworks ; but if seen from the plain, or from commanding points, a remetly must be found in simple methods : high parapets should be avoided, and traverses made very sparingl3% The slopes of the ground itself should serve to defilade in the field whenever possible. It is a fact that defilade is but a poor remedy for the defects arising from a bad position ; it is very seldom that a fieldwork can be properly defiladed ; and even when the teiTcplcin is covered, the banquettes are much exposed, and the work is unfit to make a good defence. ^ SECTION II. — Calculation of the Deblai and Remblal L ( (123). The earth extracted from the ditch must be in sufficient qu.-uitity to con- stiiict the parapet and its slopes. In permanent fortification, when time and means of transport are at our disposal, we may deviate from this rule ; but in the field w hen we are obliged to spare time and reduce as much as possible the number of workmen, the equality between ^the dcltlai and remblai is indispensable for every part of the work, nay, for every face. Even then, if .the faces are long, this condition is scarcely sufficient, since in defiladed works, where the covering mass has a greater thickness at the salients, there, will be groat difficulty in transporting ^A^ J J 132 CALCULATION OF THE with shovels tlie excess of earth from the salient to the other extremitj-. To solve the problem completely, equality should exist for every part of each face, but this would lead to inconvenience as will hereafter be seen, and we content ourselves with establishing equality for every face. For works not defiladed, and having therefore their crest horizonUd, we employ the following method, whenever expedition is required. We suppose the parapet and the ditch to have the same length, tlieir volumes will therefore be equal if their profiles are equal, and the problem is simplified into this : knowing the area of the profile of the covering mass, to calculate the dimensions of the ditch so as to make the surface of its section equal to that of the remblai. Let S represent the ai-ea of the section of the remblai. When earth is excavated, it increases in bulk, and whatever care be taken in ramming it in, the volume it occupies in the remblai will be greater than the space it filled in the deblai ; this increase or bulk, called foisonnement, is J- in strong soil, -^ in ordinaiy soil, and ^\ in sand. Represent it by -j, and let the area of the profile of the ditch = S', we should have S : y, therefore S If we take for an example, a parapet 12 feet thick with a command of'8 feet, its area is calculated by decomposing it into three trapezoids and one triangle. Trapezoid ABCD = i^J^I|~±^ x 3-75 = 25-31 square feet. Ditto . . CDLH = ^ ^ ^~ X 1-43 = 8-22 square feet. Ditto . . HLPQ =: ^-^4"^ ^ 12 = 84 square feet. Triangle. PQS =z^^-^ =: 18 square feet. S := 135-o3 square feet. and in assuming a foisonnement =z i, the surface of the profile of the ditch will be ^ S zr 120-47. 6' 5 ' ■r{i >\ DEBLAI AND REMBLAI. 133 Tliis calculation of the area of the parapet may be simplified since the surface S'9 ButFHM^FGM-FGH; FGM = and F G H = Therefore F H M = 2 FG ADFM remains constant, whatever be tlie thickness, and is equal to 22.5*53 square feet, with a banquette of 3 feet, and to 231-15 for a banquette 4 feet 6 inches wide. The area required is equal to that surface minus the triangle F H M. ^v FT- 6FG.FG _6FG'. 2 ^ ^ ^JixFG = ^' 5 FG^' Hence the total area of the profile is given by the formida S =: 225*53 ^ ^ FG being at once found by subtracting a sixth of the thickness of the parapet li-om the command 8 feet. In our case, S zr 225"53 — 4(6)- ■=. 135'53. This calculation is not long, but for greater rapidity, the following rules are given in the Sandhurst course : add the bases of the superior and exterior slopes, antl multiply by the command ; or to three halves of the command add {; of the thickness, subtract 44-, and multiply by the command. The calcidation of the ai'ea of the profile may bo simplified by a geometrical construction, which consists in drawing the profile on a large scale, say, 10 feet to the inch, and making a triangle equal to it. Suppose the parapet 8 feet high, and 12 feet thick. Draw the profile A B G D E H. Join C A, draw B M parallel to it, and join C INI. The triangles M B C, MBA, being on the same base M B, and between the same pai'allels are equal, and as the part MOB is common to both, the remainder B O C = M O A ; therefore the the two lines C B, B A may be replaced by C I\I. Again, join D H, draw E L parallel to it, and join D L : for the same reason as before the two lines D E, E H may be replaced by D L. Lastly, join C L, draw 134 CALCULATION OF THE D N parallel to it, and join C N. This line replaces C D, D L, and the triangle M C N is equal to the given profile. Measuring M N with the scale, we find it 33*5 X 8 equal to 33'5 feet, therefore the area of the profile = ^ feet. := 134 square .7^ (124). Passing to the ditch, we observe that the slopes of the scai-ps are giv by the nature of the soil (52), and that two dimensions, i. e. the width and the depth, can vaiy. In general we assume the depth, and calculate the wi(|th. Let D be the depth, x the width at bottom, - the slope of the escarp, y that of the counterscarp. ^ ^ ^ (; 'V ut ABCr _ AB BC_ 2 2 < — (- + -j. a simple The area S'=rABC + DEF + BDCE: D E F = -^, , and B D C E = D .1-, therefore S' equation which gives the value of CE. In our example, assuming a depth of 9 feet, and the slopes -j = ^, r-= i, we have 120-47 = 9 .» + V (} + i) = 9x + 33-75, hence a; =z 9-63. If instead of adopting a certain depth we had assumed the width w, the former equation becomes S' = w a; + -^ (t "^ 7 )' ^ quadratic equation. (125). This is only an approximate method of calculating the deblai, as may- be seen by the diagram. There is equality along the faces, but at the salients there DEBLAT AND REMBLAI. 135 is excess in the deblai, and at the re-entering angles a deficiency wliich does not compensate for it, the excess being always greater than the deficiency. In oitler to remedy this, the workmen wliilst excavating are directed to tlu-ow the earth obliquely towards that part of the remblai where it is wanted ; and to get rid of tlie surplus of earth either a bonette is constructed at the salient, or the material is thrown up into a glacis. In a tcnaille where there is but one re-entering angle, the deficiency is supplied by cutting into the angle of the counterscarp, but this method has the incon- venience of increasing the area of the dead angle. (126). Should a glacis be required, the ditch is first calculated as above, and to obtain the increase of width x necessary to fiu'nish earth, we have, in repre- iZJ!: senting by li and h the base and height of this glacis proximately. To prove tl: D A G E must be equal to A C B, w ,_ _Ai/. formula, let us observe, that since rectangle the depth d, ,r,f7rz — , and with the foisonnement (..i) = '^'. __ hhf f ^ ■ f- 2' '■ •''- 2d{\+f)- For a traverse, the earth is either extracted from the nearest ditch, and enters into the calculation, or it is neglected and tlie remblai taken from a ditch excavated in the terrcplein — either from a ditch of tlie usual form, or from an excavation ha\-ing a gentle slope, so as to form part of the terreplein itself. When the de- filade is practised by sinking the terreplein, the material is at once obtained. In the case of works flanked by others, ramps are frequently cut to unmask tile ditch. In tills as well as in other circumstances when the ditch proves in- 136 CENTROBARIQUE METHOD. sufficient for the defence, its width is increased, and the excess of earth thrown up into a glacis. Wlien the work is defiladed by an increase of command at the sahents, it becomes necessary to obtain the mean profile : this is done by calculating the area S, of the profile at the salient, and that of S„ of the extremity of the face, when S - ^'\^\ For field purposes the method above explained is generally found sufficient. When, however, there is plenty of time to prepare a work, a plan is drawn and more exact methods are resorted to, in order to obtain the volume of the remblai, especially when the works are defiladed. (127). Centrobarique method. A section is made in the middle of each face, and its ai'ea is calculated as above. This mean sm-face is multiplied by the mean line B, which is the path of the centres of gravity of the various sections ; the product gives the volume. This line o B may be measm-ed at the scale of the plan, and when the work is regular, this method is rapid. (128). Method of the prisms. — But when the work contains barbettes, it is preferable to divide the surface of the ground occupied by the remblai into tri- angular parts, more or less wide as the gromid is more or less mieven, endeavom-- ing also to place the sides of these triangles mider the projections of the various crests. The triangles thus become the projection of vertical prisms contained between the ground and the planes of the remblai. The solid content of each prism is equal to the area of the base or projection, multiplied by a third of the sum of its three vertical edges. The dimensions of the triangles are measured by means of the scale of the drawing, the various altitudes being also indicated by the plan. The sum of all the prisms gives the solid content of the work. These two methods may occasionally be employed together: thus in defiladed METHOD OF THE PRISMS. 137 works, wlierc tlie gi'ound is rather uneven, the volume contained between the plane of site and the groiuid is measured by the nietliod of jn-isnis, and that of the mass above by the centrobariquo process. ( 1 29). Supposing that by either of these methods the volume V of the remblai has been found, that of the ditch V is equal to •^ V. The mean section of the ditch multiplied by its length must be equal to V, but the dimensions of the ditch are unknown. Let P represent the area of its mean profile, and L its length, PL := V. Now, L does not vary much when the ditch is kept within the usual limits of 8 and 12 feet; the width at the top is never less than 12 feet, and is seldom found greater than 20 feet. We can therefore select approximately the centre of gravity of a provisional profile, and trace the line L jiarallel to the foot of the exterior slope, say at about 9 or 10 feet. The length L is measured with the scale of the di-awing, and by P L = V wc find P. With this value we can calculate tlie dimensions of the ditch as before, P rz: Do; + — ^ +-). If the centre of gravity diflfers much from the position selected, we modify it and begin a fresh calculation, or we add or subtract from tliis ditch a certain prism, the width of which is given by y, D being the difference between the volume of the provisional ditch and V. (130). This process is frequently em ployed, but there is another more exact which may be pointed out. Let V be the solid content of the face A B. The volume of the ditch, whose depth is d, must be equal to area abode (fig. 287), multiplied by the line g c passing through its centre of gravity G (fig. 288). Let us divide the solid content of the ditch into two parts : the first we may imagine to be generated by the triangle a b c, the second by the parallelogram bcde. The first volume we know at once, since it is equal to the area of a 6 c, multiplied by the path g' c', let this volume increased by -.- be represented by v. We do not know the second volume, as the side ceis the unluiown x of oiu- problem. Let G" be the centre of gravity of the jjarallelogram heed, situated at the intersection of the diagonals, and G the centre of gravity of the whole profile a. ced. The distance O G" be- CALCULATION OF THE tween G" and the vertical passing through the foot of the extci-ior slope G"/ + rf + rs+ so, and in calling h the width of the berm, G"0 :=— + (d dx. d\ , . t + 2t' / X Now, the circles described from the centre O and contained in the angle D O H of the right-angled triangle D O H, have for the limit of their development the line O H', obtained by describing an arc H h with any radius O H, and carrying the length of that arc on H H'. The line passing through the centre of gravity G" will be limited in C''. Producing H'O and g K till they meet in x, and drawing X P perjiendicular to H H', the similar triangles thus formed give X P : X s : : R IP : / C". The dimensions X P, R H' arc measui-ed with the scale of the plan as for X s, it is equal to X T + T S, of which X T is also given Therefore q" C r= by the plan, and T S already found z^b -\- —^rrT^ d X«.RH' XP ■ 2tt Putting H' R =z m, X P = m', X T = nf, wc lia^ e y fixing a piece of rope at each of them, and doubling it, the vertex belongs to the perpendicular. To drop a perpendicular on a line from a point without, drive a picket at the point, fasten to it a piece of rope suflScieutly long, and in keeping it stretched, move round until the other end of the rope intersects the line on right and left. Half the distance between the two points of intersection is the extremity of the perpendicular. (133). The tracing of open works and bastioned fronts presents no difficulty, but for redoubts or star-forts a few words are necessary. To trace a polygon of five, six, seven, or eight sides, form an isosceles triangle of cord, having for base -^, •^, 4-, and J- of the whole perimeter, and for the other two equal sides a length of fi, i^, i^, or ^ of the base. This triangle being stretched and carried, five, six, seven or eight times, as the case requires, will give the polygon. A For star-forts of six, seven, or eight salients, trace as above a polygon of six, seven, or eight sides, and on each side describe an equilateral triangle. The sides of these polygons should of course respectively be equal to ~r, ^, and -^ of the whole perimeter of the st^'-fort. (134). The projection of the superior crest being traced, the next step is the (hfilading of the work. The pickets planted at the various angles of the tracing are replaced by vertical poles, and the operation proceeds as follows : — 142 DEFILADING. For open works, a rope is stretched along the gorge on the ground, and a rule of wood is fixed along it, so as to be veiy nearly on the surface of the ground. At 8 or 10 yards in front of this line two poles are planted vertically, and a second rule of wood is moved along it by two men facing the goi-ge. An officer lies on the ground in the rear of the gorge, and places his eye close to inile A B, and command? the men who hold the rule C D, to raise or lower it, until he sees the upper edge touching the commanding ground. The Ime C D is kept in the same plane with A B by a fourth person, who, turning his back to the commanding ground, by signs, causes those who hold the rule C D to lower or raise one extremity, as the case requires. The rule C D being nailed on the poles, when the plane of sight is determined, the officer oljser\-os where the line of sight across the two lines intersects the poles planted at each angle, a man marking these points. By measuring eight feet above them, the command is obtained, and the poles are cut at tlie proper height. If the altitude D C of the commanding ground, and its distance A C to the gorge of the work are known, we can at once find the increase of command O B at the salient B, by a proportion A C : C D : : A B : B O, and B O + 8 feet Avill be the comniand. If the commanding height, instead of being in front of the salient, is on the side of a face, it is usual to make the plane of site pass only through the furthest extremity A of the line of gorge, because tlie process explained above would give too great a relief. In that case a triangle made of smooth lath, each of whose sides is from 4 to 5 feet long, is placed with its vertex on A, and is made to revolve about it until an officer lying on the ground can see its surface tangent to the commanding ground. A parados is necessary to cover the men on the banquette DEFILADING. I43 of the foec A C (fig. 298) ; aiid to reduce its height it is erected as neai- to that face as is convenient. When, instead of one lieight there are two in front of the salient, the i)lane of site must be tangent to both, and cannot, therefore, contain also the line of gorge: it is also necessary to make it pass only through one point of it In general a single plane of defilade will give too great a command, in which case we take two planes of site, and defilade separately each face from the height in front of it, and erect a parados to avoid the reverse fire. (135). This method of proceeding is called defilading by the plane of site in opposition to a less expeditious way called defilading by the plane of defilade, which consists in sending a man to the commanding ground to plant a stick 8 feet high ; a rope is then fixed on two pickets at 8 feet above the gorge, and the visual rays passing along this rope to the top of the stick being in the plane of defilade intersect the various poles of the tracing at the required heights. (136). It is not found advantageous in the field to defilade a work by sinking the terreplcin, because the earth thus obtained forming part of the remblai, the ditch destined to furnish the remainder would be too small, and would require to be widened, the excess of earth forming a glacis ; but if this method is not employed alone, it is often had recourse to in combination with the other. This hapj)ens when the command found with the plane of site is too great. In this case a first plane of site passing below the commanding ground is selected, and to complete tlie defilade by the excavation of the terreplein, a rule A B is fixed to two pickets on the projection of the crest with its superior edge in the fii'st ]>lane of site. A second rule^ is placed in rear along two poles, and the observer moves it until its superior edge, coinciding with A B, touches the com- manding ground. It is then nailed to the poles, and by its position it fixes the plane of the terreplein. 144 PROFILING. (137). In regard to enclosed works, a redoubt for instance, the process described, No. 135, may be applied, a man being sent to the dangerous points with a pole 8 feet high ; or an officer raises himself 8 feet above any convenient point of the terreplein, and a man placed on the tracing of a face, holds a measuring rod between the officer and the hill. A visual ray directed by the officer to a point estimated 8 feet above the commanding ground will intersect the rod at the point where the crest of the parapet must pass. This is repeated on the opposite face. The parados will be erected where the officer stood, its command being determined by visual rays passing 8 feet above the commanding height opposite, and 8 feet above the banquette of the face most remote from it. However, much trouble is spared by merely making the parados 3 feet higher than the parapet, as it is a command quite sufficient in most cases. (138). The defilading terminated, we pass to the profiling. //jy/ To show the dimensions of the remblai, and to guide the workmen, right profiles (fig. 300) made with slips of deal ai-e constructed along every face, some 10 yards apart. At the salient and re-entering angles oblique profiles are also erected, the position of their vertical poles being obtained (fig. 301) by the intersection of the lines passing through the corresponding poles in the contiguous faces ; the slips marking the slopes are fixed and adjusted with those of the faces, so as to form regular planes. Similar constructions are made for barbettes and traverses. (139). The ditch cannot be excavated at once in its proper shape, but it is dug by vertical layers of about 3 feet. If the lines A B represent the width of DIVISION OK LAHOUK. the ditcli at the top, wo first trace the lines C C parallel to A B, and at a distance regulated by the slopes of the scarps: in this cxamjjle both the escarp and counterscarp being at -f, the distance between A B and C C will be 3 feet. The working party excavates vertically between C C, and when the depth reaches 3 feet, new lines are traced (fig. 302) and so on. When the required depth is arrived at, the steps of the counterscarp are first cut away, then those of the escarp. ~\yr~~ (140). Division of Labour. — The workmen are divided into small squads, occupj-ing about four or five yards on the deblai, according to the nature of the soil and the depth at which they are working, a greater number being necessary for a greater depth. Ten men form a good squad. A pickaxe breaks tlie ground, two shovels (fig. 304) following, throw the earth towards the scarp, whence two other shovels throw it up the berm ; from thence again two shovels throw it upon the profile. The remblai rises horizontally, two shovels equal- izing the earth, and one man ramming it in. When tlie soil is hard, two pick-axes are necessary to occupy the shovels, and when it is very loose, one pick-axe may require three shovels to clear the deblai. As a rule, the diggers should not be nearer to one another than 4i feet. In order to place the squads on the ground, the line a b which represents the toj) of the escarp is divided into parts of four or five yards, and c d, which repre- sents the covmterscarp, into tlie same number of equal parts. In joining the points of division, the position of each squad is determined. In defiladed works the men nearest to the gorge will have completed their task sooner than those at the salients, Init when they have finished then- task, they are employed to prepare the obstacles, &c. 146 DIVISION OF LABOUR. Fig. 305. At the rate we have supposed, there will be wanted aljout two men per ruiniing yard, and as the garrison is generally calculated at the rate of two men per yard and a reserve, there will be a sufficient number of hands. Another method of di^ading the labour, is preferable for works of small profile. The workmen are told into two parties : the first have a shovel and a pick-axe each ; lialf of the second party a shovel and a rammer each, and the other half a shovel only. This arrangement permits the first party, whose work is the hardest, to change with the second without confosion, since their number is equal. The deblai is then divided into rectangles 8 yards wide, and 16 men are allowed for each. The pick-axes, 8 in number, will be in the ditch, the odd numbers Fig 306 "°^^' ^^^^ berm excavating towards the counterscarp, the even ones in the middle : these also excavate towards the counter- scarp, and when they reach it they move to the berm, and proceed as the odd numbers did, so that there will always be 6 feet distance between the pick-axes. The shovels are on the berm, the shovelled rammers on the parapet. In this method there will still be two men per running yard of parapet- When the remblai is nearly completed, fine eartli is reserved for the superior part of the parapet, to avoid splinters. The slopes steeper than |, are supported by revetments, the others are pared when the work is completed. The terreplein, if necessary, is drained. (141). The men conipusiiir;- a detiiciimeiit are usually expected to tiirow up as DIVISION OK I.ABOl'R. 147 their intrcnclnneiits tliemselves ; in some few instances, workmen are taken from among the inimbitants. It is then better to pay them by tho task instead of by tlic day, and to fix the task and the price of labour. An officer will find it tlie lu'st phm to employ at first a few men, anil to pay them well for a day or two's \vork : it will soon regulate the daily task. Field-works are often tlirown up in a great Imrry, anil care must be taken not to begin a work unless there is a certainty of having it completed in duo time. The following data will serve as a basis. It has been found that a man excavates a cubic yard per hour for a day of 8 hours in ordinary soil : in stiif clay he would only do half of it, and in dry light soil lie could dig and load on barrows nearly three times as much. The very worst worker should never do less than four yards a day, tlu'owing the eai'tli 12 feet horizontally, or 6 feet vertically. A man can wheel 20 cubic yards, or 500 wheel-barrowfuls per day to a distance of 30 yards on level ground, or 20 yards on a ramp. A horse can do tho work of seven men. Let us calculate for example, thcf time necessary for throwing up a work having a command of 8 feet, and a parapet 12 feet thick. Constructing a profile (1231 we find that the area measures 135 square feet, so that with a foisonnement of -^ the area of the deblai will measure 120 square feet. Adopting the first method for such a profile, as a squad occupies 15 feet, the solid content of tho excavation will be 120 X 15 = 1800 cubic feet, or 66 cubic yards. At tho rate of a yard per hour, this will require above 8 days' work. The following is extracted from the course of fortification taught in the French Military Schools : — " A work of 8 feet comraaud, with parapet feet thick, requires 8 days. „ 7 feet „ 7 feet „ 6 „ „ 6§ feet „ 6 feet „ 4 „ 6 feet „ 4 feet „ 2 „ " To obtain approximately the time required for a work of greater command, multiply the thickness of the parapet by the command expressed in yards ; tlie product gives the number of days. A work ten feet high, with a parapet twelve feet thick, will, then, require about .3-3 X 4= 13-2, between thirteen or fourteen days. In urgent cases this time may be reduced one half, bv excavating on both sides." For further details see 154. ^ If a work is to be thrown up in the proximity of the enemy when an attack ma}- be made before it is completed, the parapet is no longer erected at once. It is at first made four or five feet tiiiek, and in that state it is fit to resi.st nuiskutry ; h 2 1 48 FASCINES. it is afterwards widened, then raised to its proper height, the banquette and its slope being formed from earth taken fi-om the terreplein. The worlv may thus be constantly kept in a defensive condition whilst being erected ; but the ditch being rendered too weak, a glacis becomes necessary to widen or deepen it. When the remblai has been raised to the level of the banquette, working parties are told off to construct the revetments, which as we have said (51)ai-e necessary to support the interior slope. f SECTION II.— Revetments. (142). Fascines are a sort of faggot made of brushwood, firmly bound by several gads. Small fascines (fig. 308) ai'e 6 feet long and 7 inches in diameter. With stronger stuff, lai-ge fascines, 18 feet long and 6-inches in diameter, are also made. They are secured to each other by pickets, and to the parapet by a picket in the middle. The joints must be broken, and at the angles the extremities should be alternately flush. They are made as follows : Three or six tressels, according to the size of the fascine, are placed exactly in a line : these tressels are formed of strong pickets 3 or 4 inches in diameter, and 5 feet long, buried about 1^ feet in the gi-ound, and bound strongly in the middle with twigs or rope, so as to resemble the letter X. Upon tliem the brushwood is laid, and when a sufficient quantity is obtained, it is compressed to the required diameter by a choker (fig. 310), which is composed of two strong levers about 4 feet long, having a roije or a chain 3 feet long fastened to each end. Whilst two men draw towards themselves the extremities of the lever, a third bends the fascine tightly with gads : a mark made on the chain enables him to see when the 'diameter is right Five gads are sufficient for a small fascine, but a large one requires about fourteen of them. Five men can make a l;u-go fascine in one hour, and three men a small one in twenty minutes. (143). Gabions are cylindrical baskets open at both ends, 2 feet in diameter, and 3 feet high. They are placed close to each other in revetments, and can stand at a slope of -J . If used for a battery, the first row of gabions is surmounted by two rows of fascines ; if for an interior slope, the gabions rest on a row of fiiscines half buried in the banquette, and a second row placed above the whole completes the revetment. ;^ To make them, a directing circle, with an interior diameter of 1 foot 10 inches, is laid on a level spot, and from seven to nine pickets 3 feet 6 inches long, are fixed upright in the ground at equal distances on the circumference. The circle is thus raised and fastened to the middle of the pickets, and the basket work or randhtg* or iceb, is made above it, by taking three rods and twisting them alternately in and out round the pickets. When the rods are expended, others are taken and the work continues, care being taken to strike down the web now and then to make it stronger, and to fix it to the pickets by gads when it is finished. The gabion is then turned, and the other half finished in the same manner. The ends of the pickets are cut off about 1 V inches from the randing and pointed. Two men can make a gabion in three quarters of an hour. * When the web is made \rith more than two rods at a time, the process is called waling ; with two rods, pairituj ; with flat bands of three or four rods, as in basket-work, sheing ; with one rod, randing. This last requires an odd number of stakes. Among the several gabions which liavo latel}' been proposed, the most semce- able, and at the same time the cheapest, is that of Sergeant-Major John Jones (fig. 312). The pickets, instead of being round, are U inches by f inch thick. Twelve ai-e required for each gabion. The web is replaced by bands of thin sheet iron, 3.f inches wide, and of a length equal to the circumference of the gabion. The ends are fastened together by two buttons at one end (fig. 313)^ J s fitting into two slots at the other. Two men can make a gabion in five minutes. A band is put together, placed on the ground, and the pickets di'iven aroimd it alternately inside and outside : the other bands are afterwards placed so that each is outside the pickets, of which the former was inside, and they are pressed down close to each other. This gabion weighs only 26 pounds ; it is easily immade, repaired, and carried, and very rigid : it is calculated to last five times longer than the common wooden gabion. (144). Sods are chiefly employed in the field on account of the ease with which they ai-e procured. They are cut from meadows ^'°- ^•'*- previously mown and watered, but are only laid when dry, or nearly so. Good sods are 16 inches long, 8 inches wide, and 4 inches thick. Sometimes two sizes are employed : headers, 18 inches long, 12 inches wide, 4 inches thick ; stretchers, 12 inches long and wide, and 4 inches thick. They are built up like bricks, the grass downwards, the largest surface at right angle to the slope, and are fastened by jiegs to one another. One man can lay 1 9 square yards of sods in eight hours, when the sods are brought to him ready cut. They stand at ^. (145). Sandbags, made of strong canvas, are a poor revetment, but are employed when no other can be had. The bags are disposed as the sods, alternating headers and stretchers, and breaking the joints. They Fio. 315. measure 2 feet 1 inches'liy 1 foot 4 inches when empty, and 2 feet jnjfc 3 inches by 9 inches when full, and contain when full a bushel of lyP earth. Sixteen of them build 10 square feet of revetment, and tliey are disposed with tlieia' ends and sides alternately in front, the joints being broken as in brickwork. Fig. 316. By placing these sandbags on the top of the parapet, a loopliole is made which affords cover to the men when i_ firing. The great precision of rifle fire will render tlieir protection still more necessary. (146.) Hurdles are formed by driving pickets G or 9 inches upai't into the Fig. 317. slope in the dh-ection of the slope, and by interweaving twigs or rods with the pickets. (147). Planks, when they are to be had, form a good revetment; casks, trunks of trees, &c., are ;U1 also employed. It is not usual to give revetment to the scarps, except iif works intended to stand for a long time ; and where water is employed, timber revetments ai'e the best. In a paper published in the " Aide Memoire," Colonel Hamilton Smith, obser\'ing that trees in general are but little shattered by cannon shot, recommends the adoption of vegetating rami)arts. With five rows of trees planted, as in the Fig. 319. 152 COMMUNICATIONS. diagram (fig. 3 1 9 ), and kept clear of branches a few feet off the ground, the defenders will have ample material to strengthen their position. These trees prevent the enemy from seeing what is going on inside the ramparts : at the moment of need, the trees of the ditch and berm may be cut down, and be employed with those of the rampart to construct high stockades, palisades, fraises, &c. The pine, larch and fir, ho will plant 3 feet apart. He also recommends to plant on the glacis a hedge of holly or common furze. In the colonies, these hedges would be of cactus undecimalis, and the plantations of cocoa and palm trees. (148). The best revetment for field purposes is that formed of gabions, because it requires less trouble than any other, and requires less wood than fascines. Gabions stand in the revetments without fastening, can he placed by any work- man, and last longer than fascines, which requii-e skilful men, and besides do not resist so well in embrasm-e cheeks. Sods require much labom-, and a sod revet- ment takes three times as long to build as a work of brick of equal dimensions. Sandbags are expeditious, but do not last, and as they rot within two months, tliey require tarring. For the construction of batteries (96, 205) fascines ai-e, however, preferable as presenting no joints to be loosened by the explosion of ordnance. Gabions are suitable for the cheeks of the embrasures, and for traverses; sandbags are excellent for powder magazines, traverses, and mortar batteries. In the batteries constructed before a fortress, especially in those thrown up towards the latter part of the siege, these three revetments are frequently employed simultaneously. {see aho 201). SECTION III.— Communications. (149). Commu7iications. — When an open work is completed, its gorge is generally closed with palisades or clievaux-de-frise, with a barrier for the ingi-ess and egress of the garrison. Stockades may also be employed, and planted on the outline of a bastioned front, or some other tracing that will give flanking fire. Fig. 320. ire COMAri'NICATlONS. 150). In enclosed works, an opening, 2 y:ircls wide, or 6 feet 6 inches when \ destined for the passage of ai-tillery, is always left on the side the least exposed; and in order that the enemy may not see the defenders in reverse, a mass, called a traverse, is erected inside, cither witli or without a ban(iuette. These traverses can be organized defensively by forming them of two ))arts respectively crossing their fire. In the defence of a village, the above s/ disposition has been found most advantageous. In 1757, when the Austrians found it impossible to batter down the walls of Gabel with their 12-pounders, they forced open one of its gates, and some companies rushed into the town ; but meeting with traverses in their front and on Ijoth flanks, tliey were obliged to retire wth considerable loss. We sometimes heai* of cavaliy storming field-works. This is a mistake. Cavalry cannot storm a work, but may turn it, and when the gorge is not defended by palisades, barriers, &c., it can rush on the garrison, and become master of the intrenchment. At the battle of Borodino (1812), the French cavaliy thus took the Russian redoubts. A similar occurrence had taken place in 1760, near Weissen-Hirsch, when the Austrians were marching to the relief of Dresden. In forts, the opening is left in the middle of the curtain, and is covered by a small redan, or ravelin. It is either a mere palisade, itself provided with a barrier, or a regular redan, with its ditch communicating with that of the fort. In the latter case, a covered way is generally formed, and openings are made into the face of the ravelin, and also in the covered way (367). The traverse destined to prevent the enemy from du-ecting a reverse fire should be sufficiently long to intercept the whole. As a man fires at about 4^ feet above the ground, it is clear that we may imagine a plane of fire parallel to the ground, and 4 ! feet above it : this plane will intersect the profiles on both sides of the opening on lines ab, ah' (fig. .324) pai-allel to their bases, and at 4 feet 6 inches 154 TRAVERSES. Fio. 324. I E V from them. The extreme shots which the enemy can send into the work are those directed on a' b, ab'; the traverse should therefore extend 3 or 4 feet beyond the points m and n, where it is met by these two directions. In general the ti'averse will be long, and in order to diminish the labour of its construction, it is advantageous to construct a small bonnetto 3 or 4 feet thick on each side of the entrance. Many sorts of barriers are constructed : the following ai-e at the same time strong md simple, and will answer for a passage through a palisading. ■]iii Chevaux-de-fri.se may also lie employe COMMUNICATIONS. 155 All these l)arriors slioiild open internally. (151). When the work is defiladed by means of traverses, it is necessary to cut passages through them to facilitate tlio communication. These passages may be constructed as mining galleries, with frames or cases, and should be 6 feet 6 inches wide, to allow of the passage of artillery. These traverses serve also to shelter powder magazines. Advantage must always be taken of these traverses for the defence. The traverses for the defilade of Fort Little Gibraltar, at Toulon, were combined to contribute actively towards the defence, and the losses of the stonuiug-))arty testify- to their value. (152). To cross over the ditches of enclosed works, moveable bridges are fonnod ; for narrow ditches, three or four sleepers laid across, and covered with planks, are sufficient. For a greater width, one, two, or three, or more trestles, support the sleepers. (173.) When the width is small, two little wheels adapted to the bridge permit it to be moved along the sleepers. A kind of drawbridge can easily be constructed by means of two pairs of wheels. Each pair carries on it« axle a long lever strengthened in its middle, or a pair of levers of the form C B (fig. .330.) 156 COMMUNICATIONS. The platform of tho bridge is fixed to the extremity B, whilst the other extremity carries a comiterpoise made of shells or a mass of metal. The wheels being moved, the counterpoise describes a curve C c" c', and the bridge is drawn. It is maintained in a vertical position A B', by means of bolts that can be fitted into a pair of strong posts. 157 CHAPTERIXK MILITARY POSTS. ( 153). As \vc liavo said, it is not always jwssiblc in the field to throw up works witii accuracy; tlio chief of a detacliment, upon receiving news of the arrival of tile enemy, cannot waste time in calculations, but he sets his men to work at once, and makes them excavate a trench that will give a cover, which, time permitting, is atlerwards converted into a regular breastwork. Tools may be wanting ; in which case, recourse is had to such accidents as the ground may present. It would require volumes to enter into the never-ending details of the peculiar circumstances in which the vicissitudes of war may place an officer. If he is well acquainted with the principles of fortification, it matters but little if he cannot recollect all the figures and dimensions given above ; his sagacity will suggest what is best to be done. It is needless to tell him that if he has to defend a ^^llago against an enemy having artillery, lie must remove the thatch from the roofs, barricade the streets, &c. &c. A mere wall will become a good cover for him. Fig. 331. A hedge, with little trouble, will be transformed into a breastwork lo8 MILITARY POSTS. The banks of a river, when ever so little inclined, will soon become a good position. The slope of a hill, by merely cutting down the inequalities it jiresents (an operation called scarpiinj), will render his position difficult of access. The more we investigate this subject, the more convinced we become that military history is the best complement of all military sciences. There, indeed, we see that much can be done with small means. In India, sun-dried bricks, mud, and even tiers of camel saddles, have served to construct intrenchments. At Paris, paving-stones have answered the same purpose. At the attack of Edinburgh (1688), at Fort San Christoval (1810), at Bhurtpoor (1825), in America, &c., cotton bales and woolpacks have pro\ed of great advantage. At Lisbon (1810), scarping was employed on a large scale. At San Sebastian (1812), a redoubt was erected with casks to support the trenches of attack on the isthmus. At Badajoz, sword-blades, transformed into chevaux- de-f]-ise, became an insm-mountable obstacle, &c. &c. The French term passagere (temporary), applies admirably to this kind of fortification constructed at a minute's notice, with the materials found on the spot, either on the eve of a battle or for the defence of outposts. It is the application of the principles, which we have exhibited, to the various obstacles which nature offers; the strengthening of these obstacles, the combining of their properties, together with the seeking in the gi'ound for additional defensive advantages, con- stitute in fact the practical part of the science. Officers of the line are not likely to be enti'usted with the tracing of those works which a general constructs to secm-e the front or the flanks of his army previous to battle ; this care generally devolves on some officers of the engineers ; but any officer may be called upon to obtain cover for his men, to intrench a detached post, to defend a house, &c. Colonel Jebb, R. E., in his work on " the Defence of Outposts," has so ad- mirably treated this subject that we shall, with his permission, borrow from him a few pages, first, on the time necessary to obtain immediate cover, secondly, on the defence of hedges, roads, walls. &c., from 154 to 157. > TRENCHES. I59 ^ ( 154). Before entering into details, it may be right to mention as a general rule, tliat in almost all cases where trenches are required, it is essential that the means of getting out of them with facility, both to tlio front and rear, slioiild be preserved, by leaving slopes or steps for that piu-pose. Thus on some occasions it is desirable tiiey should ofter no impediment to a foi-ward or retrograde move- ment, but that troops should be able to march straight over them when necessary. In the trendies, however, which will now be brought more immediately under consideration, and wiiich are designed not only to provide cover, but to be vigorously defended when attacked, the chief object in making a step in the rear would be, that the defenders instead of waiting for the assailants in the bottom of the trench, might step out after giving their last fire, and thus interpose a fresh obstacle between them and their enemy, besides placing themselves in a better attitude for resistance. Fig. 33-i represents the section of a small trench, and tlie parapet or breast- work that has been formed by throwing the earth in front of it. The trench is 2^ feet deep, and the same width, having a rough step 1 foot broad in the rear. The eai-th thrown out will make a parapet of a height nearly equal to the depth of the trench, without taking any precaution in building it up at a proper slope different from that at which it will stand of itself; we will assume that it is 2 feet high, which will make a total of 4^^ feet from the bottom of the trench. A man, therefore, though he can reach to fire over the top of the parapet, has to stoop to be wholly concealed or covered Ijy it, and it therefore affords as little protection as can be of much sei'\'ice. From the solid content of the excavation may be determined the probable time it will take to execute it ; this is found by multiplying the depth and breadth of the trench together, for the superficial measure or area of the section, and tliat product by the length each man has to do. Here 2^ multiplied by 2^ feet is equal to 6t[ square feet; and this product, multiplied by 6 feet, which we have assumed to be the portion allotted to each workman, gives 37-1- cubic feet. The step is 1 foot broad and 1 foot deep, and being 6 feet as before in length, there will be 6 solid feet more to add, making altogether 43.V cubic feet for the solid content of the mass of cartii that has boon roinovcd. 160 rRENCHES Now, if a man is only supposed to di<; out 27 cubic teet in an hour, it will take him rather more than an hour and a half to remove 43 [ cubic feet on level ground. Fig. 335 aftbrds more cover, for the top of the parajiet is 6 feet from the bottom of the trencL The best way of executing such a profile would be to sink a ti-ench 3 feet deep and 3 feet wide, and to throw the earth about 2 feet in front of it; so that in the progress of the work, when the trench was found to be too deep to stand in, and fire with convenience over the top of the parapet, a little step might be cut out of the solid left in front, for a banquette, as shown shaded in the section ; and another step of the same description in the i-ear would complete it as far as it went. The steps might be 18 inches wide, and the same depth. The area of this section is nearly 14 feet, the trench itself being 9 feet, and the two steps 4^ superficial measm-e, which, multiplied by 6 feet, the length of the poi'tion allotted to each workman as before, gives 84 cubic feet, or about 3 cubic yards, for the solid content of the excavation ; and, therefore, under the presumed data, it would bo completed in tliree hoiu-s ; still, however, it will be observed, that it offers no impediment in itself to an enemy, and men could only be drawn up in single file for its defence, from a want of room for more. A trench of the dimensions shown in fig. 336 might be completed in five hours on the presumed data ; and being roomy enough to dispose men in double files for its defence, and high enough to screen and cover them, it may be considered as large as is necessary for merely fulfilling these conditions ; for could be dc\()tc(l to strengthening a post, or if other circumstances wr TRENCHES. It'.l it would become a consideration wliether some profile of a different form could not be substituted with advantage, for such a one as only affords cover, without opposincr any obstacle to the advance of a hostile force. Fig. 337 is a form of breastwork that might be adopted for obtaining cover in rocky or marshy situations, where a ditch or trench could not be made deeper than 1 or 2 feet ; and if there were plenty of men, they might be sot to work in two lines, and get it completed in half the time it would otherwise take, either by sinking on each side of the proposed situation, or by arranging the men in two lines behind it, as shown in the figure, where the situation for the second line of workmen is shown at (a). To work on both sides of the breastwork, which is the quickest wa}', would render it necessaiy to calculate what breadth of ground the breastwork, with its slopes to the fi'ont and rear, vvoidd stand upon, and what breadth the banquette and berm ought to be. These particulars being determined, two parallel lines would be roughly traced on the ground, with pickets, at the required distance. The work- men would be drawn up, facing each other on these lines, and woidd work back- wards, throwing the earth into the space between them, which some spare men would form into the breastwork. Here, though sinking only 2 feet, the breast- work must be raised 4i feet to obtain cover. Suppose the slope on the inside is made steep by building it up with sods, or other materials, so that it only occupies 18 inches of level ground, the outside slope, being left to find its own level, will require a base equal to its height, or 4 feet 6 inches ; and if we add 2 feet for the thickness of the breastwork at the top, it will cover S feet of ground. Then if the banquette bo made 2 feet broad, and the berin 1 foot, the distance between the two lines of workmen will be altogether 1 1 feet. Under the second supposition, if the two lines of workmen were drawn up one beliind the other, and both working to the same front, the distance between them might be from 4 to 7 feet, according to the depth. The level of the ground in this instance forms tlio banquette or stcj) to fire from. There will bo about 5 cubic vards in G running feet of breastwork, and as 162 BREASTWORKS there is supposed to be a douMc number of men at work, it ought to be finished in two or three hours.* This mode of executing work may also be adopted with advantage in other cases when time is an object, and there are plenty of hands, or when it is of importance to strengthen and give height to breastworks in particular situations. But as far as this profile is concerned, it is to be observed, that it would afford cover to an enemy when he readied it, without opposing auy impediment to his advance, which it is always very desirable to avoid. Should the ground be rocky or very hard, as in a road or street, cover may perhaps be more expeditiously obtained by raising a breastwork from rubbish or materials brought to the spot in baskets, sandbags or barrows, than in attempting to sink at all. Different expedients are shown in figs. 338 and 339. * When necessarily, the depth of a trench or ditch is very limited, the prohahle time it will take to form a breastwork out of them is more readily determined by estimating the content of the mass to be raised, than that of the excavation, as in the preceding cases, because the breadth of the latter will proliiilily be irregailar. BREASTWORK!' 1(>3 Having thus far detailed the most expeditions mode of providing cover for men, it may now be worth while to consider whether, in securing that advantage to the defenders you cannot at the same time gain another by opposing an o^'«fac/e to an enemy, by excavating a ditch m front of the breastwork, instead of making a trench in rear of it. A ditch to stop an enemy at all should be too wide to be jumped over either "flying" or "in and ont," and it should therefore be at least 8 or 9 feet broad and 6 or 8 feet deep. In more permanent works it shoidd of course be considerably larger. Fig. 340 shows the general dimensions which sucli a jjrolile might have. The ditch, it will be observed, is of a triangulai- form, and its area which must be found in order to calculate the quantity of earth to be moved, will be obtained by multiplying its breadth by one-half its depth, tliat is, 9 feet by 4 feet, which gives 36 superficial feet ; and this again multiplied by the length of the portion each man has to excavate, we will say only 4 feet, since the breadth is considerable, will be 3G X 4 ; which, considering the increase of labour arising from a greater de])th than usual, would not probably be completed in less than six hours by the same sort of workmen as we have supposed engaged in other works. Some spare men, say one-half the number employed in the ditch, would also be required for ramming the earth, and forming the breastwork. Thus, on 100 feet in length of the ditch, there would be twenty-five men working, and twelve additional, making in all 37 ; whilst in the common trench work, which has hitherto been under consideration, only about seventeen workmen have been shown to be necessary for e\ery 100 feet. A i)rofile, such as the one under discussion, therefore requires not only longer time to execute, but double the ndmbcr of men ; and it would not seem advisable to undertake it, unless there was a reasonable probability of its being completed before an attack could be made ; for if an enemy came upon it when in an unfinished state, it would be almost useless, and the lalxnir, which if otherwise applied would HJ4 BREASTWORKS. have secui-ed at least good cover, would thus be thrown away. Still, however, the advantages it offers should not be lost sight of in situations where a determined stand is to be made, and on ver}' accessible points, or where it is desirable to shut up roads, streets, &c., even if the rest of an intrenchment were differently arranged. As far as the means of resistance is concerned, it is obviously of more advantage to have a ditch in front of a breastwork than a trench in rear of one ; and the only point to be determined is whether there are time and means for executing it ; and it is on these points that an officer will have to exercise his discrimination, when he has carefully considered the various circumstances which will have influence upon it. Such a profile may further be much strengthened by planting a row of palisades in the ditch, or even by driving stakes into it, and sharpening them, or making what may be called a perpendicular abattis, by planting brushwood upright in the bottom, with the ends sharpened, as shown in figs. 341 and 342. An expeditious way also of adding to the difficulties of an assault is shown in Fig. 342. fig. 342, where common hurdles or gates, rails or brushwood, laid on the ground soon after commencing the work, with their extremities buried under the parapet, may be made use of; the earth underneath them, shaded dark in tlie figure, should be cut away when the ditch has been siuik to its full depth. Short posts laid horizontally every 8 or 10 feet in the same situation, with long BREASTWORKS. ] C;, rails or a chain afterwards nailed to them, would bo a ready expedient: the ends should project about 2 feet over the ditch, and stand at least 6 feet above the bottom of it. It is to be observed, that in all the foregoing cases only a MiNiiimi of cover AND MEANS OF RESISTANCE has bccn souglit for, in a inNiiruM of time. It has been shown what can be effected in a few hours, " faute de mieux." It may happen, however, tliat time is given to improve upon the profiles described, as would be the case if an advanced post were held for some days in succession, and each officer in command had done what he could towards it. These improvements would consist in strengtiiening the breastworks, making the ditches deeper and wider, and in planting more redoutable obsti-uctions ; and such opportunity must never be thrown away, as the means of defence, and the secui'ity afforded, will be augmented in proportion. It may be remarked that such breastworks as offer little or no impediment to the enemy, if well laid out, [jermit the defenders to charge over them in line if they wish it, and still j^ossess one of the principal attributes of any work, which is that of affording screen fi-om previous observation. But a forward movement from those that do offer an obstruction, must be through an opening, and there- fore on a naiTow front. Now the space between a breastwork and an obstruction placed in front of it is ground belonging to the defenders ; and this, if circumstances permit, should be disputed ; and as an enemy would probably be in some confusion in forcing his way through such obstruction, a favourable moment would doubtless occur for making a sudden charge, wlaich, if supported by a good flank fii-e, ought to be successful. These advantages should never be lost sight of, in arranging the general plan of defensive works, and in determining the profiles they shall have. The salient angles of tlie intrenched line are the points most open to attack, and it will be obsen^ed that the pi'ofile of the lines, terminating in those salients, has a ditch in front, which presents more or less of an obstacle; whilst the profile of the line adjoining the battery in the centre, is only that of a trench for providing cover, because it is not in a situation open to attack. When an opening or passage is required through a breastwork or stockade, it must be arranged so as to be easily closed and defended. These oly'ects may be in some measm-o secured by disposing the lines in such forms as are represented in figs. 343 and 344, and providing rough strong gates, chevaux de frize, or some- ^w 166 thing of the sort, for quickly shuttiug them up. When houses are concerned, as in a street, the barricade may extend quite across, and a communication may be made round the end of it by breaking through walls, as shown in fig. 345. (155.) Hedges, roads, ^c. — In the foregoing explanation of the details of breastworks, an attempt has been made to show tlie least possible time in which decent cover could be obtained when working on a level plain unaided by any advantages of ground and situation ; and it may be confessed that it is rather a damper to one's ardour to find, that five or six hours of hard work may be calcu- lated upon, before anything like comfort can be obtained under such circumstances, and that the men who should be kept fresh for resisting an attack, are likely to be worn out by their exertions in preparing for it. This, happily, however, is by far the worst side of the picture, for with a moderate share of luck, some little slope or broken ground will offer itself; and some hedge or ditch, bank, wall, road or wood, will be found, either placed exactly as if it were there on purpose to be defended, or a plan can readily be formed for turning it to some account. The eye is put into a man's head to be made use of, and it only i-equires a little previous exercise of that organ, to see all these natural intrenchments and local advantages in almost every possible circumstance of ground and situation. An endeavour will be made to explain by sketches the simple means which are most in use, and which appear adapted for improving, and deriving advantage fi-om such local objects as are most commonly met with, in the hope of showing that by the judicious application of a very little labour, a serious, and in some cases an almost insurmomitable obstruction may be formed. Fig. 346, represents a hedge on the top of a steep bank which has been cut down within two feet of the gromid. The branches have been carried to the front as an obstacle, and two small steps have been made on the slope, the one to load on, the other to fire from. ROADS. Fig. 347, is supposed to bo tlie same situation, but dcfcnclcd in an opposite Fid. .■?47. direction. The hedge might be felled as an obstacle, leaving the stumps 2 feet high to screen the men, or it might be cut thin and left standing, if it were con- sidered better. The slope in front is made steeper, and a little hollow is made to fire fi"om, kneeling. Fig. 348, a ditch on the side of the enemy, is supposed to have been deepened. Fig. 348. 168 HEDGES and the earth and sods formed into a breastwork on the reverse of the hedge ; where a small trench has also been made, to obtain additional cover. Fig. 349, is the same, fi-onting the other way. The hedge is felled as an Fio. 349. obstruction, or cut thin, so as to give no cover to the enemy, and is left standing^ The ditch is deepened to 6 feet, and a small breastwork is made of the earth thrown out of it, and out of a trench in the rear. Fig. 350, represents a double post and rail. Brushwood is interlaced in the front rail as an obstacle ; and a breastwork is made leaning against the other to afford cover. Fig. 351, represents a bank with double ditch. One ditch has been deepened, and the other partly filled up. Fio. 3.51. Fig. 352, represents the edge of a qviarrv or steep bank, situation. very defensible Fig. 353, a wet ditch, or brook. The breastwork i.s made from a trench in the rear. Kio. 353. Fig. 354, a road. Both fences felled as obstructions, and a breastwork placed for defending them. Fig. 355, a hollow road, arranged in a similar manner. Fio. 355. Figs. 356 and 357, arc profiles on a bare steep rock, to show the way of Fig. 356. obtaining cover in such situations ; but where means are so very obvious, it perhaps might not be considered complimentary to multiply examples. It may be remarked, that as obstructions placed under a close firo in front of temporary works are essential to their being properly defended, it will be a con- sideration whether a hedge would be more conveniently converted into such an obstruction as in Fig. 349, or made to form part of a breastwork, as in Fig. 354. A strong growing hedge is of gi-eat value for either purpose : hunting men will beai' witness that there is many a big fence, across the verdant fields of Leicester- shire, that is not to be got over by man or beast, except here and there at some "Soft placer in single file. And who has ever been out shooting, and has not now and then fallen in with a puzzler ? A small weak fence, for instance, a thing that looked like nothuig, leaning towards him from the top of a bank, but which took him something like five minutes to get over ; which five minutes, if spent within fifteen yards of a posted enemy, would have afforded time for about twelve rounds being quietly fired into his body by each man who could see him. Before setting his men to work, it is necessary for an officer to have a notion of the time it will take to execute his projected defences ; for this purpose he might pace the whole length of his proposed line, anil then by forming an idea how long it would take one man to finish a certain portion of it, say 4 or 5 yards iii lengtli in the case of deepening a ditch, scarping a bank, or felling a fence, he would see whether the number of men at his disposal could complete the whole in a given time, and would curtail or enlarge his plan accordingly, and distribute his men at intervals of 4, 5, 7 or 8 yards, as the case might bo; for it is impossible to offer any defined rules which shall apply where circumstances are ever varying. This however, must be bonie in mind, that there is more wisdom in doing a little iveU, than in attempting too much. A stick may be cut for measuring out the portions, and stakes may bo ch'ivcn in for explaining the slopes and the general form of the profile that is required. j j ij (156) Walls. — Walls arc readily made available for purposes of defence by loop-hooling them, the mode of doing it varying with their height and situation. It is a general rule that loop-holes must be so placed that if an enemy succeeds in rushing up, he shall not be able to reach close enough to make use of them ; for it is clear that if he stands on the same level as the defenders, the loop-hole \vould bo equally convenient for both parties. To obviate this inconvenience, loop-holes should be placed 8 or 9 feet above the ground on the outside ; but on the inside, tlie banquette, or step from which the defenders are to fire, should not be more than about 4 feet 6 inches below tliem, which may be assumed as a convenient height for the purpose, as already explained in treating of breastworks. A portion of the wall also, not less than 1 8 inches high, should be left above the loop-holes, where there is opportunity, for the purpose of securing the men's heads when giving their fire. These points are attainable in several ways ; and circumstances must decide which is the most convenient ; for example, if a wall were 10 feet high, the loop- holes might be pierced within 18 inches of the top, and a temporary stage might bo made of casks, waggons, ladders, &c., or an earthen banquette might be thrown up inside to fire from. Fig. 358. And in cases where a very determined rcsLstance is to be made, a second 172 WALLS. row of loop-holes might be arranged, as shown in that figure. On the other hand, if a wall were only 6 feet high, the loop-holes might be pierced 4 feet 6 inches above the level on the inside, and a ditch cut on the same side to obtain the requisite height, wliich arrangement would save the trouble of making any banquette. The quickest way of making a loop-hole is to Ijreak a wall down from the top to a depth of 2 feet, in the form of a narrow fissure, at intervals of 3 feet or more apart, and as this can be done with common pickaxes, if there are no better tools at hand, it will generally be found a more convenient mode than cutting them througli the wall, when time is an object. Such loop-holes will appeal" as shown in fig. 360. It will be seen that they are not quite so safe to fire fi.'om as others, but this inconvenience may be partially remedied by filling the upper part with a stone, a log of wood, a sand-bag, &c. If a wall should be very low, or there were not time to make loop-holes, a piece of timber, or the trunk of a tree, supported by a couple of stones, on the top of it, would be a i-eady expedient, and men could fire fi'om the opening under it. If at liaiid, sand bags, having loop-holes between them, might be placed on wall : or large stones, or sods, might be placed there in default of sand bags. A man of resource would seldom find any difficulty in adapting something to his purpose. The temporary loop-holes that are made in walls or buildings are not of course confined to any regulai- form ; they are merely ho es to fire through, made in the required direction, so that the ground may be seen as far as from within a few yards of the foot of the wall or building into which they are pierced, to the extreme range of a firelock, affording also the opportunity of firing a little to the right and left. To secure these points, the absolute dimensions will vary with the thickness and height of the wall ; the width of the hole outside, however, need not exceed about 3 inches ; but the width inside should, if possible, be equal to the thick- ness of the wall (374). The best tools for breaking looji-holes tlirough brickwork or masonry with, are short iron bars, steeled at the head, called hand-borers. They ai-e held in the proper position by one man, and strack with a sledge-hammer by another. But if men are employed who have ilot been accustomed to the use of such tools, th(!}- would perhaps get on better if each man had a crow-bar, which anybody can handle. A beginning might be made on the face of a ^vall with a pickaxe, which would verv much facilitate the work: Tiie time it will take to break 174 BUILDINGS. through a wall will be best determined by a trial on the spot ; for materials are so various, that it might lead to erroneous conclusions, were any attempt made to state a general average. Much also would depend on the tools and workmen, which adds to the difficulty of offering any precise data. A wall exposed to the fire of artillery will not afl:brd very good co\er, in consequence of the splinters that will fly fi'om the materials whenever it is struck ; but if there is time, this inconvenience may in some measure be obviated, b}' sinking a trench a few yards in the rear, and throwing the earth up against the inside of the wall : or a ditch maj' be sunk on the outside, and the earth be thrown over, as shown in fig. 363. Tiie trench is best, as it will give additional protection to the men ; but the ditch may be required as an obstacle, or to give height to the loop-holes, and therefore, as usual, circumstances must decide what is best to be done. It is not contemplated that there would be oppor- tunity for giving this embankment sufficient thickness to make it shot-proof, but most of the splinters would bury themselves even if it were only 3 or 4 feet thick. Buildings. — In his treatise on " Reconnaissances Militaires," * Major Chatelain points out most minutely the various points to which an officer must direct his attention when selecting a building for the purpose of defence ; and we shall borrow from him. As a matter of course he assumes that a careful recoimoisance will be made. ( 157) Houses. — In establishing a post in a house, the site, outline, ami size of the intrenchment are fixed. The difficulty consists in making the best of the building and its approaches. A house fulfils the conditions necessary for a good defence — (1) When it is situated at the place that suits best the ]nirpose of the post ; (2) When it commands all the surrounding ground; * ■' 'Vi-mti ties Reconnaissmices Militaires, 2 vol, Paris, 1847. HOUSES. 1 75 (3) When it furnishes the materials necessary for its defence; (4) When being of easy access, it nevertheless affords a safe retreat; (5) When its size is in proportion to the number of men destined for its occupation ; (6) Wlien the walls arc good ; (7) When its various parts mutually flank each other; (8) When it can be put into a state of defence with tlic means and time at disposal. No house fulfils all the conditions which we have just enumerated, but we remedy this by particular dispositions and additional works. To make a good defence with a house and its dependencies, we should attentively study each part and its relation to the whole; and presuming, at least, if not knowing precisely, the means of attack, we should calculate the means of defence on tlie strength of the detachment combined with the resources to be derived from the locality. All this implies a minute and careful reconnaissance. Almost every house, even in ordinary conditions, differs fi-om any other, either in the site upon which it is built, in its dimensions, in its distribution, or its dependencies. Tlie site. — The post which always requires the most attention is that which is situated near the most important passage, or on a communication which it is desirable to close against the enemy. Whatever may be the configuration of the groimd, tlie house ought to be isolated from everything that smTounds it, and should not be commanded by a height or another house ; but it ought always to be near the passage intended to be guarded. We should select, within the limits which we shall presently give, those houses that best suit the locality. Dimensiom. — If the house belongs either to a sinijile agriculturist, workman, or keeper, it will pi-obably be small and possess but little solidity, and will rarely be capable of a good defence; a farm with several bams and stables offers few resources, few dwelling i-ooms, and only occasionally a yard and a garden, which arc mostly badly walled in. An inn will be larger in comparison, as it is situated on a more frequented road, and at a convenient distance from a town for post- horses. Country houses are also to be met with, of one or more stories, with yards and gardens. Industrial establishments, such as mills, ironworks, paper nianufactoi'ies, &c., consist of groups of buildings, and some have several stories ; water is generally found there, of which use can be made in the defence. Distribution. — A house contains rooms or halls, the size and disposition of which are to be studied, in order to knojv well the manner in which each part ought to be defended; the same for doors and windows. Barns, coach-houses, and stables, occupy the ground-floor, or form distinct buildings. Tlie yards are enclosed by buildings, or merely by walls, palisades, &c., the same as gardens 17fi HOUSES. and parks. The ground-floor will be moi'e useful if it is elevated a little above the surrounding ground. If the house is isolated and composed of a single block, the project of defence will be easy and simple ; but if it forms part of a group, we must keep well in mind the disposition of tlieSc houses compai'ed with the combinations of the defence. If the detachment is too weak to defend the group, it is necessary to demolish the contiguous houses, or at least to knock off the crest in order that they may not command it. If it were more advantageous to defend them, they must be joined to the principal building, and easy communication covei'ed from the enemy's fire must be established between the one and the other. The construction. — If the house is of wood or thatched, the enemy could burn and destroy it, unless the defenders build around it an earthen intrenchment, hiding from his view the most exposed walls, or may erect hlinded cover on their sides (485). If the roof is of straw or of sliingle it is indispensable to demolish it. When we have time at disposal, we also take down the roofs of tiles or slates to make use of the material, or to avoid their being splintered by the cannon. Brick walls are the best, because a shot only makes its own hole in them whilst in walls built of rough stone, or even of cut stone, it throws over whole blocks. Stories above the second one are often injurious, because a ball reaches them easily, and the debris incommodes the defenders. Shots fired from these stories ai-e besides too plunging. A thickness of wall from 1 to 2 feet is the most advantageous, because it offers the desirable solidity, and is easy to pierce for loojiholes. Old walls offer little resistance ; very old houses are not capable of a good defence. Dependencies and approaches. — The dependencies are blocks of buildings sepai-ated from the rest, as stables, coach-houses, workshops, enclosures of yards and gardens, &c. Only those objects which can be made useful in the defence should be preserved. We should not forget that the house is the principal object, the reduit of the system of defence. Trees, to the distance of 200 yards from the position which might favour the attack of the enemy must be cut at the height of two feet from the ground ; the same with hedges and thickets. Ditches and holes in which the enemy may find shelter must be filled up. The enclosm-e walls, outside the position to bo defended, which might afford any aid to the enemy, nmst be demolished, and the materials must be spread about so as to prevent any midulation. Stacks of wood or hay found near the position must be burned, reserving always what is useful, can-ying it quickly into the magazines of the army. In a word, we should endeavour to isolate the house, to cut down anything which facilitates the approach, to level the ground aromid to a distance of 200 yards, in order that the enemy may be seen from the position fi'om head to foot, and even to render impracticable the roads in the neighbourhood exce])t that of retreat. HOUSES. 177 Of the means to prepare for the defence. — In the first place, for the execution of the works, endeavour to procure the necessary tools, such as sjjudes, shovels, pickaxes, hammers, saws, pinchers, wheelbiurows, eai-th or sand bags, cords, ladders, &c. A few, no doubt, will be found in the house or the environs. In many instances different materials are also wanted, such as beams, planks, boards, nails, stones, &c. ; the house itself or the neighbouring houses will probably furnish them. Nevertheless, it is possible that a p:u-t, or even all of these objects, may be wanting, and, time failing, the dispositions for the defence ought none the less to be made with the means we already have. If there are inhabitants at a little distance, tliey can be employed in moving the earth or transporting materials. The defence of a house comprehends the measures to be taken in the interior and exterior. In the interior. — Doors which open outwards must be strongly barricaded within. One of them must be ai-ranged so as to open for going out, if a moment arrives when a longer defence becomes impossible. The windows are barricaded also by means of planks or a double row of boards ; iu default of wood the wintlows must be stopped up with casks or sandbags, and the same measures are taken with regard to the openings leading to the cellars, so that the enemy cannot throw powder or other incendiary projectiles. The principal door must be covered by a tambour of palisades or stockades in the form of a redan flanked by the interior of the building, pierced with loopholes. If the door, thus strengthened, cannot offer an efficacious resistance, an abattis, barricade or other obstacle must be established five or six paces in the rear, from behind which a few men can defend the entry to the house. The interior doors must be partly barricaded, there being left at each sufficient passage only for one man. Large stones, trunks of trees or furnitm-e should be ready near these doors to obstruct the passage after retreat. Loopholes must be pierced round the ground floor, eitlier in the walls or the fastening of the doors or windows, and also near the angles of the building. The upper stories must also be loopholed, but less closely than in the ground floor, because only a few men will suffice to fire into the hollows adjoining the house. When the ceilings are lofty, two rows of loopholes are made, and the superior one is reached by means of a banquette or scaff'old. If there are balconies, they are furnished with mantelets or beams; and flanking fire is thereby obtained ; and in cutting openings through the floor or flagstones above the door, we obtain machicoulis from which the foot of the wall may be seen. If the enemy is able to attack with artillery, it is necessary to prop up the floors near those walls which are too weak to resist the shot. If great breaches are to be made in iho walls, an intreiichnient should be made behind, from which llie 178 HOUSES. enemy could be opposed when atteinjiting to ])enetrate. Loopholes might also be pierced into the partition walls, to facilitate fighting from one room to the other. If the defenders have cannons, they should be placed on the spot exposed to the first attack, such as the angles of the house, or in the direction of the roads that lead to them. Besides, embrasures should be cut through the doors, and closed by shutters. The staircases leading to the upper stories must be demolished, or if time is wanting, they must be blocked up with casks, great stones, or other objects, to render them impassable ; they may be replaced by moveable ladders, which may be carried away by the defenders. The entrances to the rooms, coach houses, or other places which are not to be defended must bo blocked up. One of the remotest parts of the house, the one that is the least exposed to tlie first attempts of the enemy, must be chosen to form the reduit and magazine, or place of arms, in which is placed a portion of the provisions and ammunitions. Should there be a tower or a keep, a reduit is made of it. The dispositions of the defence of this part are made with particular care, and so connected with the rest of the building, that the retreat thereinto may be easily made, and that the enemy may not be able to approach it. The first floor requires similar means of defence to those of the ground floor : the windows are barricaded and pierced with loopholes ; the walls should only be pierced when the windows are too far apart. If an escalade is feared, at the foot of the exposed windows, an opening in the floor must be made in the form of a ditch, which must be covered with move- able planks to approach the loopholes without accident. These openings also serve as machicoulis for the defence of the other rooms of the ground floor. In case of an urgent retreat, two windows on the first floor are reserved in which the barricades are easily taken away, so as to aftord means of escape by the help of ladders. If there is no time to take off the roof, as befoi'e said, openings must be made through it, in which skilful marksmen are put to keep off the enemy if he attempt to escalade over the top of the house. It will be prudent to spread over the floors dung or rubbish, about a foot thick, to avoid fire, and if the floors be not strong enough for this overweight, it will be necessary to prop them up. Tubs and casks filled with water are carried up to the first story ; and also planks, stones, and utensils for boiling water, and for throwing it on the enemy if he attempt to escalade, &c. On the outside. — Tambours arc built up on each side of the house similar to the one established behind the entrance door, or they are constructed at the angles in order to flank the circumference better, if the sides of the building are lon^ : and the walls are piereed to commniiicato with Fio. 364. 17!) )f these works. A machicoulis gallerv may bo constructed on the fii-st floor; when there are halconies this is very simple; when none exist, some construction of timlxjr, as in tiiis diagram, will be found advantageous, cither above the door, or along the whole front of the house. Outside tlie house a triangular ditch is dug, two yards deep; the slope resting on the walls ought to be higher than the ground, so as to leave no bcrm which the enemy might use for escalading or for stopping up the loopholes. If the yard is surrounded by coach houses, stables, &c., they must be prepai-ed in the same manner as for the house, according as time and means permit, that is to say, we barricade the openings, pierce loopholes, and contrive some means of communication between them, so that the taking of one does not entail the loss of the other. An enclosure wall must be loopholed, even in two rows, if high ; the loojiholes pierced at one foot from the ground are the most dangerous to the assailant; a little ditch is dug inside to serve as a banquette. Very rarely can a wall of this kind resist cannon, but it can be strengthened with earth banked against it. A hedge replaces palisades, and if it is higher than a parapet, we make a banquette. The exterior part must not be intrenched before being sure of the means of defence for the house, and unless the force of the detachment enables it to be done. With a garden enclosed by walls, the same precautions are taken as with a yard. When the house is situated on level ground, it may be surrounded at eight or ten yai-ds by an intrenchment with ditch and parapet, forming a first enceinte, or by abattis or pahsatles, according to the importance of the post. (158). Faksis. — An isolated farm house diflFers from other houses, because the enceinte is more extended; it has generally numerous buildings about it: barns, stables, workshops, &c., surrounding several yards. These premises, almost N 2 180 CHURCnES. always situated in the centre of the ground to be cultivated, often occupy a good position in a line of battle, in which case we intrciicli in them several battalions and some artillery, so as to resist several attacks. More frequently still, an isolated farm house is occupied by a detached post; and all that we have said concerning a house is applicable to it, or at least to a great part of it. Sometimes a farm house is an old country or pleasure Iiouscj or is composed in part of the ruins of an old castle, of which some great walls are remaining, capable of making a good reduit. The first examination of a locality ought to determine which part of the building will be reserved for the defence, according to the force of the detachment ; this part must be isolated from the buildings, and intrenched in the manner explained above. A convent or an old abbey may be ranged in the same category. Chueches. — In many counti-ies churches are to be found isolated, when, for instance, the houses of a village are dispersed, or when it serves for two villages. They are also sometimes in the centre of the place, but are rarely so situated that they can be approached under covei*. They must be isolated, even from the rectory house, if this is likely to damage the defence. A church almost always unites more defensible qualities than a house ; it is, therefore, a good post. Churches are rarely commanded, and are generally surrounded by a cemetery, which often forms a good intrenchment. Still, the cemetery must be altandoned if the detachment is too weak. Houses and trees in the neighbourhood furnish means of defence for the church. A large church can be defended by a weak detachment, because the troops are not subdivided. The walls are stronger than those of private houses: they almost all resist cannon; loopholes are pierced between the pillars. Cimrches in the shape of a cross can give flank fire. Amongst the means of intrenchment given for houses, those for the church must be chosen for the interior and exterior, according as they agree with the ground. Rows of loojjholes can be multiplied ; the galleries and pulpits serve very usefully as intrenchments ; stones and paving stones must be carried to the top of the church, to be thrown down on the enemy during his attack. Tlie choir, choir gallery, and the vestry must be individually retrenched, and made to communicate with one another. The chairs and seats serve to make good barri- cades. The steeple will be the last retreat in which the garrison can defend itself. Castles. — We meet frequently, especially in mountainous countries, with very strong old castles, of which some are abandoned and in ruins, and of course uninhabitable, and others more or less in a state of preservation. These castles are sometimes the best posts to defend. Abandoned castles are for the most part invaded by the neighbouring forests ; ISOLATED MILLS. Isl tliey are surrounded by wide and deep ditches; tlioir walls arc very thick, and are pierced with numerous loopholes, and surmounted with machicoulis. These forts have often several enceintes, flanked by a strong tower, and closed by double gates, some of which are still furnished with a portcullis; but the walls are damaged, the vaults broken in, the ditches partly filled up, and the interior parts without fastenings and filled witli rubbish. Nevertheless, the walls present such a solidity, that by means of a few dispositions, a vigorous resistance may be made; and in order to ensiu'o this, clear away the foot of the breaches, barricaarallel to one n\rr» made of tree;^ 197 lother about six inches from the end, by two slings three inches in diameter. KiG. 379. Smaller ropes, called braces, are attached to the slings between every pair of casks, turned round the balks, and agaui lashed to those of the opposite side, and firmly secured. Fio. 380. zEzn iiizn The casks may also be enclosed in an open frame of woodwoi'k. These piers are excellent, but they should be at least 20 feet long. (171). Eafts made of trees bound together and stiffened by cross and diagonal Iji'aces, are not so good on account of their small Ijuoyancy. Their cliief advan- 198 FLOATS.— TRESTLES. tage is that they cannot be desti-oj^ed by the enemy's artillery. Their length should not be less than 45 feet. Fig. 381 shows the disposition of the rafts con- stinicted in the French ser\-ice. (172). Floats may be made of the skins of the animals killed for the army. An ox hide may be made to form a float capable of carrying 300 pounds. Each skin is cut into a circle of from 5 to 6 feet in diameter, and its edge is gathered round a short tube, to the inner end of which a leathern valve is nailed. It is inflated with bellows. The back part of the skin is not good, and should be tarred. These floats are used as casks, but they require re-inflating every ten or twelve hours. They should not be employed when the velocity of the current exceeds 6 feet per second. (173). Trestles bridges are constructed, when floats cannot be procured, for shallow rivers having a firm bed, and the velocity of which is not much above 4 feet per second. Trestles are made of any material found on the spot, and are secured in their place by putting stones or shot inside their legs, and by lashing their heads to a rope stretched across the river. An additional leg may be given to the end down the stream. The usual dimensions for the cap piece are from 12 to 15 feet long, and from 9 to 12 inches square. The legs are made of timber, from 6 to 9 inches square, tlir distaiu'c between the feet being about lialf the ROrE nRlDGES. 190 height. The braces may be scantlings 8 inclies by 2. They are never higher than 10 feet, and they are placed from 10 to 15 feet from centre to centre. (174). Piles are used when the river is rapid, muddy, and wide, more espe- cially if the bridge is intended to stand a long time. For the passage of infantry alone, and in shallow rivers, the piles are di-iven in by means of heavy mauls ; but wlien they are destined for artillery, they must be driven in by a monkey made of a heavy shell filled with lead. The piles, 1 foot in diameter, pointed and often capped with iron, are bm-icd 9 feet, cut to the same level, and fitted with a head I)iece on which the balks are placed. The number of piles in each row varies with the width of the bridge ; they are usually 3 feet apart. The rows or piers are* as far apart as the length of the balks will allow. (175). Rope bridges are not recommended; they arc costly, cumbersome to carrj^, and liable to destruction through alternating dampness and dryness. They liave nevertheless been frequently employed. As early as 1515, the Swiss con- structed a rope bridge across the Po near Casale, over which tliey transported their artillery. The French did the same in their campaign in Italy in 1742, and in 1792 there was a regular rope bridge in the service. Dm-ing the Peninsular war both French and English had recourse to them. In 1810, the French having destroyed an arch of the bridge of Alcantai-a, Colonel Sturgeon re-established the communication with ropes. This bridge consisted of a network of rope fixed to two moveable beams, stretched at each side of the arch by five blocks of pulleys fixed to a strong sleeper secured in the masonry. This network was supported besides by three hawsers stretched tight between the two sleepers, and prevented from oscillating by the guys underneath. Over the network cross beams rested, which supported the balks and tlicir chesses. In a system successfully tried at Metz in 1827, the sui)erstructure consists of transversal beams supporting the balks and chesses. These beams are borne by susjiending ropes attached to four strong cables, two on each side, passing over horses 12 feet high, and sti-etched by means of 8 blocks of pulleys fixed to strong ^w-^N-^ V s, which are secured in the gi-ound at a depth of G feet. Lateral oscillations are prevented or at least diminished by two ropes, crossing each other several times under the flooring ; they are fixed to the ground and maintained in their position by rectangular frames, which have pulleys at their angles on which the ropes run. The vertical oscillations are prevented by guys underneath. (176). A large river is not likely to arrest an army, because the necessity of providing means of passage has been foreseen, but a small stream, a canal, a broken arch, &c., may cause a serious interruption in the march. In such a case every available means becomes valuable. A small detachment may pass over a LEVER BRIDGE.^ 201 tree felled from the bunk, or over one felled from each l)aiik : tlio branches en- tangling themselves secure their position, and the axe soon cuts a passage. A few ti-ces lashed together into the form of a raft, and secured by one end to the bank, will, when set afloat, be carried across by the cm-rent itself, and serve as a bridge or for the foundation of one. A lever bridge is made \t\ burying the trees in the banks so that the parts uied overwcigh the rest, and if the trees are too short to meet, their extremities Fio. 390. arc connected by short ones made fast to them. In 1811 the French in this manner repaired 20 yards of the bridge of Moreilla on the Alva. Fig. 392. ^'o^l^g trees may form bridges of the rustic ord^ 202 PLYIN{4 BRIDGI When the depth of the water is not more tlian 4 to 5 feet, wagons may l)e employed instead of trestles. Fig. 393. A gun limber placed vertically and secured by ropes, may su])i)ort frames or ladders on which planks laid across form a flooring. FlO. 394 Gabions of a large diameter have occasionally been employed : they were laid horizontally and covered with fascines. - / (177). Flying bridges serve to convey troops aci'oss rivers on which a floating or fixed bridge would seriously interfere with the navigation. They also serve to pass detachments over, previous to the construction of a regular military bridge. They are especially adapted for rapid rivers, and arc very common on the Rhine and Danube. A flying bridge generally consists of a raft of two boats, or of one boat only, THE TRAIL. 203 anchored in the middle of the river, with a cable usually equal in length to 1 V the widtli of the stream. This cable strongly secured uj) the stream, is supported by Fig. 396. . Kio. 397. I'lo. 398. ])uoys or boats. It is attached, near the stern, to a windlass, and ti-averses on a horse erected near the bow, at about ', of the length of the raft. The rudders gi\o to the raft a proper direction Floating wharfs arc constructed on each bank to facilitate landing and embarking. If the river is very wide, a wharf is fixed in the middle, and two flying bridges are employed. The angle which the raft makes with the current varies with the length of the mooring. When the cable is only half the width of the river, the angle at depar- tiu-e is 90°, that of arrival 0° ; when it is equal to once the width, these angles are respectively 68° and 40° ; and when the length is 1 J the width, they are 64° and 44". As a rule the raft should always make an angle of 45° with the cable. (178). The trail is a raft warped across a stream by means of a chain or rope Fio. 399. stretched from bank to bank. A rope is attached to the raft or boat, and by means of a peculiar pulley, called traveller, slides along the chain. The cun-ent Fio. 400. m 1 a» ^oj •■ ^ ^ i 204 FERRIES. causes the raft to pass when its surface forms an angle of 55o with tlie direction of the stream. It is pi'eferred for rapid and moderately wide rivers. A trail may consist of a rafl ha\'ing the form of a rhombus with angles of 55°, attached to the chain by two ropes. Fig. 401. (179). Ferries are flat bottomed boats with moveable gangboards. Such a boat is carried across by means of a rope stretched across the river, on which the men pull. This rope may partially dip in the river and rest on two supports fixed to the boat. In 1796, at Placentia, Napoleon conveyed 500 men and 50 horses at a time across a ferry. (180). To complete this chapter, wc may add a few words on the selection of the point of passage and on the details relative to the calculation necessary for the construction of a bridge. When the passage of a river is likely to be disputed, the best position for a bridge is on a bend, presenting its concavity towards the enemy, because it affords greater facility to concentrate fire upon him, more especially if the opposite bank is commanded. There should be in front sufficient space to allow the army to take position after its passage. The bank should be high, because in sudden rises shallow banks cause rapid alterations in the width of the river, but high banks arc seldom found in bends. When the passage is not to be disputed, the straight pai'ts of the river are the best, since the bed is less liable to vary, but a passage should not be attempted immediately below a bend, or at the confluence of a river, or at a town in possession of the enemy who might send fire-rafts, &c., to destroy the bridge. Islands may sometimes be turned to advantage. The reeonnoissance or information received from the inhabitants may lead to the discovery oi fords. They are chiefly found in the rapid parts where a straight river widens, or obliquely across a bend. The depths should not exceed 21 feet for artillery, 3 feet for infantry, and 4 feet for cavalry. The width of the foril, is indicated by pickets, the cavalry passes up the stream, the infantry lower down. BUOYANCY. 205 he may sen'O for tlio paRsape of infantry when 3 inches thick, of liglit artillery wlion from 4 to 6 inches, and for any weight when above 6 inches. Even when tlie thickness is not sufficient, passage may be obtained by laying down straw to the depth of 6 inches, and pouring water on it; the water rapidly freezes and will carry. (181). Before constructing a floating bridge, it is necessary to calculate the weight it has to carry, and the number of floats. The latter depends on their buoyancy, and on the scantling of the timber used for balks. ' ' ' ~ The weight to carry is that of the troops, and of the superstructure. An infantry soldier fully equipped weighs 15 stones, a horseman 18, a horse 9 cwt. 2 stones. Every man occupies 20 by 20 inches, and every horse 3| by 9^' feet. A 9-poundcr gun and carriage with limber and ammunition weighs about 38^ cwt., and with the horses, occupies 40 feet in length. An 18-poundcr ditto weighs 66, V cwt., and occupies 50 feet. The weight of the superstructure is found bj- nudtiplyiiig tlie solid content expressed in cubic feet by the specific gravity of the material, and the product by 62lbs. The solid content of squared timber is found by multiplying the mean breadth by the mean thickness, and the product by the length : that of round timber is obtained by multiplying the length by the square of the quarter of the mean girth. SPECIFIC GRAVITIES. Elm Cherry tree — Oak (seasoned). Teak Maple Plum tree Apple tree Alder Ash Beech Olive tree •G73 •715 •743 ■750 •752 •755 •793 Iron (bar) 7-700 | Larch -530 Iron (cast) 7-264 j White Pine -551 Tin (cast) 7-291 Cedar -561 Steel 7-816 I Willow -685 Brass(cast) 7-824 ' Sycamore -604 Copper (cast) 8-788 ' Chestnut -604 Copper (sheet) 8-910 j Lime tree -604 Lead 11-352 Pear tree -650 Cork -240 Yellow piue -652 Ash -845 Poplar (common) -383 Red pine 657 Beech -852 Poplar (Spanish) -529 I Walnut -671 ' Olive tree -9-27 The buoyancy of a float is ascertained by expressing in cubic feet the solid con- tent of the part to be sunk, and multiplying it by 62 lbs. The product, minus the weight of the float, is the l)Uoyancy in poimds. To find the weight which planks, trees, rafts, &c., would carry before sinking, e.xpress their solid content in cubic feet and multiply it by 62 lbs., and the product midtiplied by the difference between 1 and the specific gravity of the wood, gives that weight in pounds. For casks, the solid content is found bvthe formula -01309 L (D- + d' -f- 4 M-) in which L represents the length, Drf, the inside diameters of the two ends and M the diameter of the middle, all expressed in inches. The product divided by 277-27 gives the capacity in gallons. The lunnlier of gallons mnltiidied by / Z )l*^ 206 BUOYANCY. 10 gives the displacement in pounds, and the displacement, minus the weij^ht of the cask is the buoyancy. The Aide Memoire gives a list of naval and com- missai-iat casks: — Puncheon 72 gallons Weight 1351bs. Buoyanc}' 694 Hogshead 54 „ „ 109lbs. 576 Barrel 34 „ „ 7 libs 407 Half Hogshead 2G „ „ 591bs. 292 Kilderkin 18 „ „ 451bs. 194 Tierce 37 „ „ 581bs. 428 Irish barrel 25 „ „ 471bs. 275 (182). The transverse strength of beams, as given in the Handbook for Field Service, is found by the following formula. LetC=z — p where b — breadth, d:=: depth, Zr: length of given beam, all in inches. Let S be a co-efficient, depending upon the nature of the material. Good bar iron S = 6I50 Pitch pine =1632 Cast iron S = 7644 Norway pine := 1474 Teak wood S = 2462 Riga fir = 1080 Ash S = 2037 Larch from 842 to 1138 Oak from 1081 to 2261 If the beam is supported at one end and loaded at the other, the utmost weight it will bear W = s c. If it is supported at one end, and the load distributed over its whole length, the weight W rr 2 s c. If it is supported at both ends and loaded iu the middle, W =: 4 s c. If it is supported at both ends, and loaded uniformly over its whole length, Wi=8 sc If it is supported at both ends and loaded at a distance m from one end, w = s4t^ 7/1 {I — m). In practice, the beam should not be exposed to more than half its breaking weight. As for the strength of cordage, the same Handbook gives the following nde : the average breaking weight in cwt. of sound hawser-laid rope under 5 inches in circumference, is 4,l times the square of the circumference in inches : above 5 inches it is 4 times the square of the circumference. Cable laid rope is not so strong as hawser laid. The weight itself of the rope is found by multiply- ing the length in fathoms by the square of the circumference in inches, and dividing the product by 480, the quotient gives the weight in cwt. DEFENCE OF mUDGES. (183). When an army has constructed a bridge which is intended to stand during tlie campaign, either to facilitate the arrival of drafts, convoys, &c., or to secure its line of retreat, it is necessary to defend its approach by works which, according to the importance of the operations, will he eitlier a mere redan or a •rown work, or even a system of detached works forming a retrenched camp. Fig. 403. ..^^r~^7^-x This api)lies also to permanent iiridgcs, the possession of which is considered necessary. It rarely iia|>pens tiiat more th;ui, three bridges can be constructed at 208 DEFENCE OF BRIDGES. tlie same point : for a numerous army however, it is advisable to liavc two bridges for infantry and cavalry, and one for artillery and heavy waggons : this prevents confusion, one bridge serving for troops going one way, the other for those going another. Such bridges are usually 100 j'ards apart, and the works for their defence have necessarily a certain magnitude. Under all circumstances these tetes-de-pont should be defiladed from the neighbouring heights, and contain palisaded reduits covering the bridges, and at the same time ])ermitting the free movement of troops, for advance or retreat. Flanking defence is obtained from batteries established on islands or the opposite bank, and the outline should be powerful enough to enable the garrison to withstand an assault. If the enemy can come on either bank, double tetes-de-pont are constructed. (184). To prevent the enemy from desti-oying a bridge by sending heavy floats, fire-rafts, infernal machines, &c., down the stream, it is usual to establish a boom across the river, about 1000 yards above the bridge. It is made of trunks of trees joined by iron rings and chains, and is inclined at an angle of 22" with the Fig. 40.5. banks, so as to diminish the impulse of these floats and facilitate their removal. Posts of observation are enti-usted with their guard. CHAPTER XII. VAUBAN'S FIRST SYSTEM. (185). When a town is to be fortified, we suppose it to be sm-roundeil Ijy an Fio. 406 imaginary figure, a, t, c, c?, e, /, called a Folygon. The sides ah, be, &c., ai'c called Fronts. (186). When these fronts are of the same length, and the angles of the poly- gon equal, the fortification is called Regular. When, owing to the accitlents of the ground, hills, rivers, &c., these fronts and angles are not equal and equidistant, the fortification is called Irregular. The study of regular fortification forms the basis of the science ; it is the pro- vince of the engineer to apply it to irregular sites in the best manner, a task sometimes eminently difficult. The fronts being supposed to be equal in length, and exposed to the same dangers, it is evident that the combinations of their defence must be alike ; therefore the object of the study of Permanent Fortification is to find a perfect outline for one fi-ont — a problem still to be solved. (187). The vai-ious lines constitjUting the trace or outline of a front, form what is called a SysUm of fortification, and as every system results fi-om a particuliu- combination, it bears a particular name, usually that of its inventor. The number of these Systems may be said to bo indefinite, several hundreds 210 VAUBAN'S FIRST SYSTEM. having been successively proposed, and many being still brought forward every day. The outline of a system is independent of the length and disposition of the fronts, and to facilitate the construction, rules or fornmla; are laid down for every one of them. To understand thoroughly the combinations adopted for the defence, it is necessary to be familiar with the method of attack, and we shall therefore begin by giving the outline of a system (one of Vauban's, for instance), and by explain- ing the process of attack, before any further consideration of modern improvements. (188). Vauban, a French general officer (16.33-1707), is the author of sevei'al systems which bear his name. He never gave rules for their construction, but fortified towns as he found them, improving the fortifications ah-eady erected, and making the best of the sites. His name has become very popvdar, and in England he is generally considered as the inventor of the whole science. Such is not, however, the case ; distinguished engineers had before him greatly improved the old outline of the clumsy bulwark, and his first system is but a slight modification of one in use before his time. (465, 275.) He has done more against Fortification than for it ; it is he who discovered the ricochet fire, and so much improved the means of attack, that the defence has ever since been unequal to it. His successors, in comparing the various fortresses he constructed, ha'fe for the sake of convenience classified them into three systems. The second system is to be fomid only at Beford and Landau, and the third at New Brissach. To the first belong upwards of thirty places which he entirely constructed, and many more that he merely improved. This system we shall select for example, and exjilain it as required from Candidates for Military Service.* But it must be borne in mind (and this we shall see hereafter), that Vauban had no fixed system at all, and that many modifications of the following method are to be found in his fortresses ; still, as the formula adopted gives all the leading featm-es of his early methods, we select it. The line of front A B =z 360 yards. Fio. 407. * Before 1858 every candidate for the army was expected to draw the outline and tlie profile of Vauban's first system. It is for them that most of this chapter was written, and as no other knowledge of fortification was required, it was necessary to lie very explicit. Hence the elementary iomi of this chajitcr. THE MAIN DITCH. 211 The capitals of tlio two bastions arc next drawn. As they bisect the angles of the polygon, the angle which they make with the line of front is equal to half the angle of the polygon. Wo learn from Euclid that n being the number of sides of the polygon, any angle =^^^-^^ ^ ^ Tlie capitals make therefore with the front an angle of 45° for the square, of 54 for a pentagon, of 60 for a hexiigon, &c. In our example, we have selected the hexagon. The perpendicular = A of the front for the hexagon and all polygons of a greater number of sides, -fth for the pentagon, and J^th for the square. The faces = -fths of the front. From the angles A, B, of the polygon as centres, and with a radius =: the distance to the furthest shoulder angles, if arcs are described intersecting the line of defence, the chords of these arcs gi\e tlie flunks, and by joining then- extremities the curtain is formed. Tlio main ditch is obtained by describing from the salients as centres a circum- ference, with a radius of 30 yards for a dry ditch, 36 for a wet one. Tangents to these arcs, drawn from the shoulder-angles, give the counterscarp. The Tenaille, in the Main Ditch, coincides with the Line of Defence; its thick- ness is 16yai'ds. Its extremities are parallel to the flanks of the Bastions, and 8 yards from them. In the square and pentagon, the perpendicular being shorter and the angles less obtuse, the gorge of the tenaille thus traced would not leave sufficient room before the curtain : it is therefore necessary to draw the gorge a h parallel to tlio curtain and at or 7 yards from it, the escarp C(/ being as usual 16 yards fm-tlicr. r 2 VAUBAN'S FIRST SYSTEM. Fig. 410 Tlie salient of tlie ravelin is on the perpendicular at 100 yards from the re- Fio. 411. entering angle of the counterscarp. Its faces are directed to a point 10 yards fi'om the shoulder-angle of the bastion. The ditch of the Ravelin is 20 yai'ds wide, and its counterscarp is parallel to its faces. In the main ditch, and between the tenaille and ravehn, a double caponier is usually ])laced ; its crests are parallel to the perpendicular, and 6 yards fi-om it ; the foot of its glacis is parallel to its crests at a distance of 20 yards. A passage of 3 yards is reserved between the head of the caponier and the ravelin. The Covered icay is made 10 yai'ds wide, and its crest is parallel to the counter- scarp. At the re-entering angles, by setting off 30 3\'irds on each side, and drawing the faces, (7 6, (Zc, at an angle of 100° with the (iriginal tracing, the lic-enterithi TRAVERSES. 213 Place of Arms is found. The terrepleiu of the covered way, at the salients, S, S, S, forms tlie snlienf places of arms. The foot of the glacis is parallel to the crest of the covered way, and 50 yards from it. Traverses are constructed in the covered way; they are 18 feet in thickness. Those that enclose the salient places of arms are formed on the prolongation of the faces of the ravelin and bastion. At the re-enteriug places of arms they are perpen- dicular to the counterscarp. In the middle of the branches of the covei'ed way of the ravelin there is another traverse, also perpendicular to the counterscarp. Passages called crockets are made around the head of eveiy traverse : to trace them in the outline, the crest of the glacis is di-awn parallel to the head of the traverse 4 yai'ds from it, and then to the front and rear, at a distance of 5 and 8 yards respectively. r The first line of parapet that encloses the place, consisting of bastions, flanks, and curtains, constitutes what is called the Body of the place, or Enceinte. Within the glacis, works like the tcnaillo,* caponier, ravelin, covered way, &c., ai"e called Outiro7-ks. Any work erected beyond the glacis, and witliin muskoti-y range, is denominated an Advanced Work, to distinguisli it from Detached Woi-ks, which are beyond range, although connected with the general defence of tiie place. 214 VAUBAN'S FIRST SYSTEM. (189). The following cuts contain the profiles of the various parts of this front ; the line A i? represents the level of the ground in Figures415, 4l6,417,and418; a b the level of the covered way in Fig. 419, and cd that of the main ditch in Fig. 420. Fig. 415. JS^-ncei/rvte. The rampart follows the outline of the crest of the bastion, having in its centre ti interior space on the level of the ground, — tlie bastion is then called Empty or FLAT BASTIONS. ; Hollow. If tlie interior is filled up to tlic level of the terreplein oftlic ramp; the bastion is called Full. A flat bastion is one whose denii-gorges are in the same straight line. 216 VAUBAN'S FIRST SYSTEJI. (190). Along the ramparts, ramps, from 4 to 6 yards wide and 20 to 30 yards long, are constructed to facilitate the passage of men and artillery. The figures 422, 423, 424, represent these ramps at the salient of the ravelin, on the curtain, and on the flank of a bastion. The communication between the jilace and its outworks is established by means of a postern or gallery, under the curtain, opening at the foot of its escarp. A vaulted passage under the tenaiflo leads to the counterscarp of the ravelin. Staircases called pas de souris, give access from the ditch to the teirepleins of the ravelin, of the tenaille, and of the re-entering and salient places of ai-ms. They are 6 feet wide and 36 feet long, except for the tenaille, in which they are only 30 feet long. They are either single or double. Those at the salient places of arms before X the bastions are circular and described, as the figure shows, with radii of 90 and 96 feet. The centres of the arcs are found by the intersection of two circles of 90 feet radii, described fi-om the foot and the top of the staircase respectively. It is usual to leave 18 feet distance between the double staircase, measured on the foot of the counterscarp. • SALLY PORTS. Fio. 427. The covered way communicates with the country by Sally Forts, or cuttings, 4 yards wide and 8 yards long, made in the glacis, in the middle of every face of the re-entering place of arms. To mask them from tlie view of the enemy, they are directed towards the adjacent salients of the covered way. {See Fig. 421.) The crochets are 9 feet in the cleai' ; the dimensions given in the outline allow for the various slopes : they are 4, 5, and 8 yards in round nimibers, cvactli/, 11, 16, and 231 feet. The banquette of the covered way as well as that of the traverses, is pro\adcd with a row of palisades ; the crochets and the sally-ports are closed with barriers. Tills palisading is generally dispensed with until the jilace is threatened with a siege. (191). To separate wet ditches from dry ones, a wall, called a. Batardeau, is built across ; and to prevent it fi'om serving as a passage, it forms an angle at the top, and a tower of solid masonry is erected on its middle. In these batai-dcaux sluices are usually placed, in order to fill up the dry ditch, if necessary, when the besieger attemj)ts to carry his approaches there. Batardeaux are generally con- structed at the salients of bastions. (192). Vauban has given tOvthe revetments of the scarps a slope of i tor all heights, thereby obtaining massive walls for low scarps, and weak ones for high relief. These walls, 4 or 5 feet thick at the top, are strengthened by buttresses, or counterforts, on the rear, the eft'ect of which is to relieve the wall, and to resist 218 VAUnAX'S FIRST SYSTEM. the breacliing Ijatteries more eftectually than a plain scarp of superior thickness (see 322), they stand from 16 to 18 feet apart. r—m \ The foundations are 3 feet deep, and their breadth exceeds hy 18 inches that of the revetment. At the top of the escarp a coping-stone, A, ])rojects, to prevent water from running along the slope and filtering through the joints. It forms a coutinuous cordon all along the magistral line of tlio enceinte and of the ravelin. The wall of counterscarp is can-ied up to the head of each travei'se. Such is the first System of Vauban. To understand its value it is necessary to know the method of attack to which it must offer resistance, and this we shall examine in the next Chapter. Though the chief reliance is placed on musketry in the defence, it is none the less a fact that artillery is the essential element in the defence of a fortress. Bousmard calls it the soul of a place ; Carnot says that a fortress is but an immense battery, &c. To the garrisoning and armament of fortresses, we shall direct our attention ; of course tlie guns ai-e emplo3'ed chiefly on the front attacked, — some flanking the main ditch, some that of the ravelin ; others on the capitals of the Ijastion or ravelin commanding the approaches, and on the faces of the latter a few guns flank the salients of the bastion. 219 CHAPTER XIII. ATTACK OF A FORTRESS. SECTION I.— Irkegulau Attacks. Permanent Fortification, wo repeat, cannot be learnt unless the attacks he thoroughly understood. We shall therefore dwell on this subject, and after having discussed the method adopted for the attack, we shall give the conduct of the defence, both being so intimately connected that any attempt to study them separately could but bring confusion. The hostile efforts directed against a fortress are of two sorts : to the first category belong all those that are not regulated by fixed rvdes, to the second tliose that are conducted according to rules given by experience, the ensemble of whicli constitutes the art of sieges. (193). — In the first place is the surprise, which is now of very rare occurrence. Its success depends on secret intelligences with persons inside the place, and on the manner in which the service is performed ; it is usually combined with attacks of Vive Force. But the garrison must bo weak, and the scarps easy of access. Secrecy and rapidity of execution arc most essential, since, in case of failure, the retreat must be made under the fire of the place. Besides, the forces must be considerable, for the garrison may rally to a central point, and then charging the scattered columns of the assailants, easily overpower them. Prague, garrisoned with 2000 regular, and 3000 irregular troops, was surprised by tlie French in 1741. Schweidnitz, with 3000, was taken in the same manner by General Laudun in 1761. Owing to a door badly constructed, through which the French musketeers found an entrance, Valenciennes was taken in 1667. Great danger, liowever, attends these operations ; and although the Crimean army has been found fault with for not attempting to take Sebastopol by a coup-de-main, yet it acted according to the rules of experience. At Cremona, in 1702, Prince Eugene contrived to enter by night with 4000 men, and to carry off the Governor, Marslial Viileroj-, l)iit an Irish regiment eventually drove him away. At Berg-o|>- zoom, in 181-1, the English had already surprised and occupied several bastions, yet they were repulsed with considerable loss. It is important to know the dispo- sition of the works, the depth of the ditches, and the height of the scarps ; to provide the men with ladders of proper length ; to be aware of the negligences habitual in the ser^'ice, &c. The attacks should never be attempted at night ; the scarps of the ravelin being often mistaken for those of the enceinte, the columns lose their way, and the confusion becomes great. Early in the morning is the best time. The columns of attack must be strong and well supported ; the commanding officer should be a man of action and well acquainted with what he has to do when once in the place, or when he has to retreat. These attacks are only made now when some urgent reason, such as the arrival of hostile reinforcements, compels the general to make a desperate effort before retiring. (194). Scaling ladders arc now made in lengths of 12 feet, and tapering so as to fit into one another. They weigh 50 pounds each. Their exti-emitics are provided with staples for fixing them together, and they are secured by lashings. m Each joint, when thus fixed, gives an effective length of 10 feet. Smaller ladders, 7 feet 6 inches long, are also made, and in order to employ tlioni simul- taneously with the othei's, they have the same width at top and bottom. A wall from 1€ to 18 feet high, requires 2 lengths; from 18 to 28, three; from 28 to 35, four. As a rule, the ladder should over- reach the height of scarp 3 feet, so that it may be placed one yard from the foot of the wall, and also assist the men in stepping from it upon the wall. Two men carry one length, and three men a double length. When a fortress is to be escaladed, a previous reconnoissance will ascertain the heights of the scarps. The men intended for the operation are divided into two equal portions, the storming party and the covering party. The ladders ai-e prepared in lengths and double lengths, and laid on the ground out of sight of the enemy. The storming ]>arty divided into sections of five proceed to the ladders, three men taking the double, two men tlio single ARTILLERY AITACK. 221 lengths. They move on, carrying the ladders on tlieir right shoulder, and having their muskets sliuig over the left. They are guided by engineers, and accompanied by sappers ; the covering party lies fiat on the crest of the glacis, ready to fire at tiie parapet should the defenders attempt to prevent the escalade. The ladders are applied to the counterscarp, and when the storming party is in the ditch, it proceeds to the escarp with -} only of the ladders; those left at the counterscarp will enable the covering party to come to dieir support The ladders are planted firmly; but if they are found too short, they are raised, and an additional length is secured below. The men then fix bayonet and ascend. It is proper to give a sap-hook to each leading man, to enable him to secure a good footing, and give iissistance to those that follow. A new kind of scaling ladder has been lately proposed by Mr. Fawcus. It is only 6 feet long, and weighs 25 pounds. Tiie lashing is done away with, and the lengths are secured by bolts. (195). Another sort of attack, which has been called Artillery attack, may succeed when the escai'ps are low and exposed. It consists in opening a breach at 600 yards distance, or even further if necessary. Approaches (206) are then rapidly executed up to the ditch, without giving time to the defenders to throw up intrencliments, and a constant fire of' mortal's and howitzers is kept up on the breach until the moment of attack. In a day or two the breach can be made. Ciudad Rodrigo, and Badajos, were breached in this manner. (196). Bombardment has generally but little effect, since both the men and ammunition in a garrison are usually pi-ovided with bomb-proof shelters; the strength of the fortress is not much impaired, the houses alone suffering. With populous to^vns, little disposed to resist, it may answer; but if the garrison is determined, shelter will soon be constructed and fires extinguished. These attacks are of difficult execution, and require enormous power of transport. (197). Blockades are resorted to against a garrison abundant in men, but badly provisioned — which happens more frequently than is generally supposed. In 1806, after tlie battle of Jena, the French found large bodies of Prussian troops lieaped, so to speak, in fortresses. In that case it is essentially necessary to blockade exactly all the circumference, and to occupy vigorously all the strong jioints, in order to suppress any attempt on the part of the enemy to evacuate. (198). Siciie. — Regular attacks proceed more slowly, but are more certain; to take up a position round the place, intercept all communication witli the exterior, ajiproach nearer and nearer to the crest of the glacis, open a breach in the enceinte, reach the garrispn, and compel it to surrender, — such is their ensemble. These attacks once begun must be carried on witliout interruption, otherwise the garrison will construct new intrenchm^-iits, replace its parapets, and organize 222 SIEGE. a more powerful defence ; they should therefore only be undoiiaken when there is a certainty of the arrival of tools, artillery, ammunition, &c. Tliis question of tools and implements is very important, and although their quantity varies with the strength of the place and that of its garrison, yet an idea may be formed by observing that the most recent sieges give, as necessary, an average of 7000 pickaxes, 10,000 shovels, 3000 axes, 5000 hatchets, besides special tools for sappers and miners. The implements required are 7000 fascines for trenches, 100,000 ditto for revetments, 20,000 gabions, 10,000 fogots for sa^jping, 50,000 * sandbags, besides a proportional number of pickets, hurdles, sap rollers, blmds, &c. SECTION II.— Siege. Section a. — (199). The first operation made by a besieging army is the Investment of the place. Its object is to cut off all communication witli adjoining towns or corps of troops, to prevent the garrison from getting rid of encumbi-ances, to lay hands upon all neighbom-Ing and distant resources, such as corn, cattle, wood, &c., to intercept any detachment not actually in the place, and to favour the reconnoit- ring — an important item, which will spare false movements and loss of time. To insure success, the investment should be sudden. It is generally carried out by detachments of cavalry and field-artillery, or of light infantry, according to the natui'e of the ground, which during the day keeji themselves out of range, and approach nearer at night. Their strength varies with local circumstances, and their march is regulated so as to bring them at the same time before the place. The investment should be complete, otherwise the besieged will be enabled to receive reinforcements, as was done at the siege of Namur in 1695, at the attack of Flushing (1809), or to cause serious annoyance, to the besiegers, as atBadajosin 1812. The army follows one or two days after. In the mean time, the position of the camps has been determined by reconrioitring ; they are usually out of range (three thousand yards from the glacis), and the best use is made of the ground to conceal them from the views of the place. Sometimes barracks are constructed. The parks of artillery destined to receive the ordnance stores and ammunition. • At the siege of Gerona (1809), by the French, one battery of 6 pounders alone required 80,000 sandbags. At Constantino, in 1837, the number of sandbags employed in the construction of the batteries vvu!- THK POINT ()!•" ATTACK. 1>23 and the engineers' park for the tools and implements, <.*te., are formed at the same distance. Whilst the troops are encamping, field-works are thrown up to occupy the chief points and protect the parks and magazines of all sorts against surprise ; and such bridges, trenches, &c., as are necessaiy to connect tlie investment, are cousti-ucted. In early times it was customary for the besieger to intrench him- self between lines of coutravallation and circumvallation, the former to resist the sorties, the latter to protect the rear against any attempt made to force him to raise the siege. This method is now oljsolete. The lines of coutravallation are to a certain extent replaced by the trenches themselves, and a few redoubts on the Hanks. As for the lines of circumvallation, experience has proved that they are dangerous (81) as defensive positions, unless the enemy can i)rcsent himself on a limited front only. It is better, in case of an attack on the rear, to leave sufficient forces to guard the trenches, and to march to the enemy. (200). In the meanwhile, officers proceed to make accurate reconnaissance of the place, in order to determine \X\o point of attach During the day, they advance witli a small escort to within 400 or 500 yards of the glacis. At night they endeavour to reach the covered way, fathom the depth of the ditches, &c. The reconnaissance should be made so as to leave the enemy in perfect ignorance as to which front it is intended to attack, otherwise he will lose no time in strengthening it, by all the means he can dispose of uand.tp^d^iCjeiyeiLimj false attacks have sometimes been made, as at the siege of Quesnoy in-l794i The general plan of the place, and of the surrounding countiy, is kept by the engineers, who sketch every day on it the works destined to be constructed during the follo\\dng day, and definitively trace the works executed the day before. It is usually made at the scale of -rn-iTTru j the plan of the attacks as far as second parallel is on a scale , „g„„ , and that of the rest on a scale -yinjiny- Plans of most fortresses are always to be had: the reconnoitring party then completes the information. In the selection of the point of attack, the natiu-e of the soil has a great influence, a rocky soil being an insurmountable obstacle. Marshy and gravelly soils ai"e to be avoided, as well as those which are liable to be iniuidated. A river is also a serious obstacle. The configuration of the ground is next considered. When it rises towards the place, it fiiciUtates the defilade, but is very disadvantageous for the batteries ; hollows ninning perpendicular to the front are dangerous, but a ridge aflbrds good support to the trenches, anc^ may eventually mask them. It is important to direct the attacks upon pouits where a superiority of fire can be obtainetl ; therefore re-entering angles and straight lines are left, and salients are selected. These are examined, as well as the works that supjiort them; their ■224 THE POINT OF ATTACK. Hank defences, the height of their escarps, their dry or wet ditches, the number of out\voi-ks to be successively carried, the facilities for the besieger to throw up intrenchments on these points, &c. The proximity of woods, the facility of commimication, the line of retreat, &c., all influence the selection of the point of attack. The point of attack being selected, the commanding officer of engineers, assisted by the officer commanding the artillery, draws the project of attack ; and the commander of the forces decides, in case any difference of opinion should arise. This project generally embraces one front only, and consists of three partial attacks, one on the ravelin, and one on each bastion. Attacks on tno fronts require a very large force, and if the two fronts are not contiguous, they demand a double army. When the angle of the polygon is very obtuse, it is better to attack two ravelins and a bastion, otherwse the collateral ravelins AA would become a serious im- pediment, their fire taking the besiegers in flank. If the angle of the polygon is not very obtuse, it is better to select two bastions A and their ravelin ; the collateral works give but an oblique defence, :ind the besieger has the advantage of giving two simultaneous assaults on tlie body of the place. (201). During the investment and the reconnaissance the tools and imfilements are collected and prepared, if this has not been done before, and according to the estimates of the engineers, the necessary number of gabions, fascines, sap faggots, sap rollers, ])icke(s, etc., are made. I'ROLONfiATION OF FACES OF ^V()RK^ : Length. Diameter. „. in. 9 1 li i 2 2 9 t n 1 4 Weight. Time for execution. fl. in. 6 3.T lbs. 2 cwt. 401b." to 50 601b. to 70 301b. 6 cwt. to 7 lib. 2oz. 601b. Three men in 20'. Fonr men in 2 hours. One man makes 25 in one hour. Dicto One man makes 50 in one honr. Two men make one in 20'. Ditto One large fascine sawn into 6. 1 Three men in 17 hours make 1. ' One man sews one in 40'. Fiiscinos, large 18 IJ 3ito4a. 2 9 3 3 6 6 2 8 Revetment pickets Gabions for sap Gabions „ Sap faggots Sap rollers., j ?»^^,f ^»|^-; Sand bags.. ^™'"J; ;;;;;;;;; (202). It is also of the utmost importance tliat the prolongation of the faces of the works of the fi'ont of attack should be accurately determined ; and the position of the capitals ascertained, and marki'd by pickets, on the ground. This is some- what difficult, because the glacis now marks the masomy, but in watching the green slopes in the morning and in the afternoon, the various shades of light they present serve to guide the officer in his reconnoissance ; he must occasionally ascend a small ladder, when the sun does not shine. If the slopes are clearly seen, the prolongation of the capitals is at once obtained by planting two pickets in a line with the intersection of the parapets at the salient angle, and the intersection of the crests of the gla'cis. If this is not possible, the prismatic compass will answer the purpose (fig. 435) : measure the bearing « of a A, and then /3 of -ft . "2- g'' b P., then 226 FIRST PARALLEL. Fig. 43.'). capital ; after tliis, aim at the salient, and move about until the compass bcai> ^— , when a point of the capital will be found. (203). First Parallel. — Let us suppose that the attack is made on a ravelin and two bastions. The first step is to throw up a continuous inti-enchment that will serve as a basis to the subsequent operations. It is parallel to the general contour of the fortress : hence its name of " parallel." It is constructed at 6^0 yards from the most advanced salient of the place, because at that distance the troops employed to break the gi-ound arc not much exposed to grapcshot ; the garrison cannot hear the noise, and is too far off to attempt a sortie ; besides, experience shows that, at this distance, three-fifths of the rounds fired from the batteries established before the parallel take effect. At a greater distance than 600 yards the practice would become too uncertain. Sometimes an accident of the ground permits the parallel to be established at a smaller distance. In 1794, at the siege of Maestricht, a hollow within a small distance of the place served to establish the extremity of the parallel. At Bouchain, a hollow within twice pistol range allowed the besiegers to construct a place of arms the first night of the opening of the trenches. At Limbm-g, the dragoons succeeded in forming a lodgment within pistol range, under cover of some hedges. At Bayonne, in 1814, a hollow road parallel to the works enabled Wellington to come within 240 yai-ds of the place. At Malta, in 1800, fences of stone were similarly turned to account by the besiegers. AtTortosa, in 1810, Marschal Sucliet oi)ened the trenches at 300 yards, being TRACING THE PARALLELS. 227 fnvoured by a heavy fall of snow. At Antwerp, in 1832, the Frencli opened theirs at 400 yards, being covered by hedges and garden enclosures. It is sometimes necessary to construct tlie first parallel at a much greater distance than 600 yards, when the nature of the ground renders the construction of the approaches (206) difficult. At the siege of Ypres, Friburg, Mons. Namur, Maostricht, Gibraltar, etc., the ricochet batteries could only be opened at a distance from 1000 to 1200 yai-ds. The tracing of the parallels, duo to Vauban, who employed them for the first time at the siege of Maestricht, in 1673, is very important. The parallels must embrace all the works that command a view of the attacks, generally the collateral fronts. They enable the besieger, with immense advantage, to repel the sorties, to flank his further advance, to protect his batteries, and to connect all the attacks. The first parallel is traced on the gi-ound by means of pickets, close enough to guide the engineers diu'ing the night, and this is usually done at dusk, a short time before the working party begins, piccos of tape connecting the pickets to prevent mistakes. Between the first parallel and the parks, at 1200 or 1500 yai-ds from the place or where\-er convenient, depots, or stations, for the tools and material necessary for the daily supply of the trenches, are established, and their communications with the pai-allel are traced at the same time. When these tracings are completed, the number of men necessary for the excavation is easily calculated, each man being allowed 6 feet. (204). At night-fail these workmen are collected in the depots, where they receive a shovel and a pick-axe each, and arc formed into as many columns as tliero arc capitals crossing the parallels. It is important to deceive the garrison as to the time fixed for the " opening of the trenches," therefore it is only at night that each detachment, about 25 strong, commanded by its officers and guided by engineers, marches to the tracing of the parallel, filing off right and left as they arrive there, and lying flat on the ground ; the engineers ascertain that the men follow exactly the outline, and place themselves 6 feet apart, and to make this sure, each man is sometimes made to carry, as in the French service, a tracing fascine, which he places in a line along the tracing. At a signal, the whole working party begins to excavate, throwing the earth in front to obtain immediate cover. These workmen arc protected by a guard, calculated at three-fourths of the gan-ison: the cavalry are at the extremities of the parallel ready to charge; the infantry takes up a position in front or in rear of the parallel: the different battalions detach pickets in front, and these again send vedettes and frequent patrols. The covering party should avoid firing on small sorties, but repel tliem with the bayonet, and retire into the parallel when it is sufficiently forward to att'orrl oo\pr. Q 2 228^ PROTECTION OF WORKMEN. / I During the first night tlie parallel is excavated 5 feet wide and 3 feet deep, and / the communications with the depots are also executed with the same profile. Fig 436. Next day, both workmen and guard are reheved, and the trench is widened to 10 feet, slanting in the reai- to carry off the water and defilade the space, the guard taking position in the parallel itself. Fig. 437. In general, working parties are relieved every twelve hours, at dusk and at day- break, the works being begun at night. To enable the guard of the trenches to fire over the parapet, t\vo steps, sup- jioi-ted by fascines, are constructed in the space between the capitals, and in some Fig. 438. paj-t of the parallel similar steps are cut on both sides of the pai-apct, to permit Fig. 439. ^f^^ the troops to clear the parallel easily, in order to march against the sorties of tjie besieged. The profile of the parapet of the trenches is not sufficiently strong to resist artillery, but the defenders will not waste their ammunition in attempting to destroy it. The chief protection afforded by the parallel is concealment from the enemy's view, the troops being scattered behind an extensive line, it would hardly be worth while for the garrison to fire at them at random. The extremities of the parallel are usually secured against flank attacks by redoubts. :^^ lyl^- 229 (205). Battenes. On the second niglit, wlicn tlie first parallel is completed, the besieger constructs his batteries to subdue the fire of the defence, and to permit further advance upon the place. They ai-e constructed in front of the liurallel (at a distance varying from 30 to 50 yards) and rarely in the parallel itself, because they would obstruct the movements of troops, and more rai-ely still in rear of it, because the fire might inconvenience the men in the trenches. But this depends much upon the locality. The ricochet batterieis are established perpendicularly to the prolongation of the faces which :u-e to be enfiladed. They may receive from 3 to 6 guns to ricochet the terreplein of rampart of the ravelin or bastions, and 2 howitzers to ricochet the covered way. The space between the prolongation of the parapets and ditches affords in these batteries room for a few mortars. Those batteries which are intended to silence the works which cannot be enfiladed, are placed dii'ectly opposite them or wherever convenient: they are called counter latteries. All these batteries are distinguished according to their nature, as: Cavalier batteries, when the platforms of the guns are above the ground ; these are only employed when tlie inequalities of the ground would intercept the shots. 230 BATTEIUES. Elevated batteries, wlien the platform is on tlie ground. This is tlie sort most generally employed, especially for counter-batteries ; and the only kind which can be constructed when the gi-ound is marshy. Sunken batteries, where the level of the platform is 3 feet below g'roimd, the soles of the embrasm-es coinciding with its surface. These are objected to because the necessity of excavating the whole terreplein, 30 feet more or less, entails much V labour ; the terreplein, sunk at first 3 feet to get cover, must afterwards be filled 6 inches ; no platform, no revetment, &e. can be fixed until the excavation is completed ; the embrasures cut through the parapet are invariably badly made ; the foundation for the platform is often too uneven, and the magazines being on the ground are not so well covered. It is only when a parallel is transformed into a battery that this kind is advantageous, since part of the work is alread}^ done, or when the ground falls to the rear. Should the ground rise to the rear the terre- plein must be sunk, but the labour is much increased. Half-sunken batteries are preferable, especially for ricochet, because the guns require no elevation, and there is no danger of seeing the shots intercepted by rising ground, whilst they require much less time for their construction. In common soil and vmder ordinary circumstances, the elevated batteries should be completed in 36 hours, the half-sunken in 24 hom's ; but all of them should be finished before they open fire sinuiltaneously, because if they were to open their fire in succession the enemy might destroy them in concentrating bis fire on each. The parapet of these batteries is made 18 feet thick, and an epauhnent is thrown up at each exti-oniity to cover the gunners ti-oni tlic ()blii|ue tire of the collateral PUWDKK MAUAZINK!- 2:n works : it is usually 12 feet thick. Splinter-proof traverses 6 foet thick at the bottom, and 6 or 7 feet high, and 16 foot long, are erected between each 2 or 3 giuis ; they are perpendiculai- to the parapet, and about 2 feet from it, thus leaving Fio. 445. ■"^m^ a passage for the men to make their escaiie from that part of the battery in which a shell falls. To order the working party destined to construct a battery, we suppose (he work to be dixidod into as many portions as there are gims, reckoning an ejiaul- nient as a portion, and the parapet before each traverse as half a portion. From 9 to 13 men are allotted to a portion. The platforms for guns, 9 feet wide by 15 foet, have a rise of half an inch to the foot, to diminish the recoil: mortar jilatforms hitherto 8 feet square, and now 9 feet wide by 7 feet 6 inches, arc laid hoi-izontal. Foiu" men can lay a platform in one hour. Mortal's requu*e no embrasure; they are placed 15 or 18 feet apart, and removed to a distance of 12 feet fi-om the epaulment when fired at 40° elevation. This distance must be increased when the angle of elevation is less. The superior slope of the pai'apet generally couuterslopes. The batteries arc armed at night, the guns being taken across the country, since the bottom of the trenches would be too soft. Fifty men can drag a 24-pounder. Powder magazines arc placed either in the epaulments or 30 yards in rear- of the batteries. The expense magazine holds sufficient ammunition for 24 hours' firing, and feeds 3 or 4 pieces. A laboratoiy magazine serves for the whole battery the piu-posc of loading the shells, weighing their charge, and fixing the fuzes. The form of these magazines varies (figs. 446, 447). We represent here the form which is most recommended. Fig. 448 is a section of a magazine in tlie epaulment. Fig. 446. Fig. 447. I, ■ ■ . ' '-- ■ -t-1 m =e APPROACHES. (206). When tlie Ijatteries are constructed, the besieger in order to advance towards the place, executes covered roads or trenches in the shape of zig-zags, called approaches, zig-zags, or hoyaux. They are not directed in a straight line towards the place, because they would be enfiladed, but proceed obliquely. They follow the capitals, crossing them alternately right and left, because it is the shortest direction they can follow, and also because they do not obstruct the fire of the ricochet batteries ; they are besides less exposed in the undefended sector. These zig-zags are very neai-ly limited in length by two lines intersecting the first parallel, at about 70 yards from the capitals and converging on the salient at- tacked; the labour is thereby limited to what is sti'ictly necessary; and the changes of direction, an operation more or less long and dangerous, are rendered less frequent. The prolongations of these zig-zags should always fall clear of the most advanced salients of the collateral fronts, at 20 or 25 yards fi-om them, as Vauban recommended. A return of 30 feet is made at every extremity to cover the approach in rear from the enfilade fire which the enemy may dispose of in sorties, and also to allow room for tools, &e. They should not form with one another an angle less than 30°. They may be made 1 foot less wide than the ])arallcl, and 6 inches deeper, because more cover is required on account of their ..l,li, jUlt SECOND PAKALLEL. 233 C\ I Skction c. ~ (207). Second parallel. On the fourth night tlie approaches have reached half way between the fortress and the first parallel, and a second pai'allel is con- structed, but if the batteries hove not slackened the fire of the defence, it is neces- sary to wait a night or two more. This parallel is traced by the engineers, and at dusk the working party is collected and led as for the opening of the trenches, every man carrying two sap gabions, a shovel, and a pick axe. Arrived on the spot, they place their two gabions 2 feet beyond the tracing, and lie flat on the ground till the signal is given for the excavation to begin on all the line. The gabions are filled up in 15 minutes, and afford a musket-proof shelter. This process is called the Fli/iny Sap. The first night the excavation is made 5 feet wide and 3 feet deep, each man completing his 4 feet, and leaving a berm of 1^ feet A covering force in the approaches, or in front if the ground permits it, protects the workmen. Next day the work is completed as for the first parallel, and the gabions are crowned with one or two rows of fascines. Banquettes are also erected for the guard of the trenches, tmd steps cut to pass over. This parallel protects the working parties in their further approaches, and without it they would be nearer to the enemy than to their own supports. As is seen by these profiles, the second parallel has a greater solidity, being provided with a revetment, to resist the projectiles. This parallel is protected in flank by redoubts, or is connected to the first by zig-zags. When the ground masks some of the batteries of the first parallel, or when, owing to the obliquity of the faces of the bastions, these batteries are too far to produce effect, they are constructed afresh on the corresponding points of the second parallel. This is done in two ways, either the parallel itself is transfonned into a battery, in which case trenches are excavated some 20 yards in the rear to keep up tlie commmiication, or the batteries are constructed in front of the parallel. In this case, which occurs when the line of fire is rather oblique, a Hying sap is carried out to the |ioint, where the coiuiterscarp of the epaulment is 234 DEMI-PARALLELS. intended to be, then it turns round following the counterscarp of the parapet. This flying sap serves as a screen, behind wliich the men construct the battery. At night the guns ai'e dragged across the countrj'. (208). Demi- Parallels. — From the second pai'allel the besieger advances again in zig-zags, till he amves within 150 yai-ds of the crest of the glacis, where his proximity renders the sorties more serious ; then he is obliged to excavate Demi-Parallels or Places of Arms, or portions of parallels destined to contain a strong guard, to protect the workmen and quell the musketry of the place, A, A, A. (Fig. 449.) These places of arms, from 10() to 150 yards in length, extend right and left as far as the prolongation of the covered way of the ravelin, or the re-entering places of arms ; they are widened at their extremities to receive light mortars or howitzer batteries, which throw stones or shells along the covered way, to keep down the musketry fire ; the fiu-ther progress of the attack depending greatly upon the result of this. (209). After the second parallel, the flying sap can seldom be resorted to, because the musketry of the defence begins to tell, and grapeshot to harass the approaches. It becomes necessary to advance more carefully, and therefoi'e more slowly. The zig-zags are no longer made by placing several gabions at a time, but by disposing them one by one. This Regular Sap is entrusted to Sappers and Miners, organized in as many brigades as there are lines of approach. A brigade consists of eight men. It cannot be midertaken on open ground, but it is begun from a parallel or a zig- zag, and proceeds in the following manner: — A sap roller (or large gabion 6 feet long, and 4 feet wide, rendered bullet proof by means of another gabion 6 feet long and 234^ feet wide, placed inside the first, with the interval filled up with stout pickets) is passed over the parapet of the parallel by means of two spars and rojics, and an opening is made into this parapet by removing two gabions. Sapper No. 1 places a gabion behind the end exposed to fire, and to make room for it pushes the sap roller by means of two sap forks, or long poles. Provided with hooks, he then excavates a trench 18 inches wide, and 18 deep, leaving a berm of 1 foot, and with the earth fills the gabion. Another gabion is placetl beyond the first in the same manner, and a sap faggot. STANDING SAP. 235 or two sand bags, aro placed opposite the parts where tlie gabions are in contact to protect that weak part fi-om musketiy. The sapper continues in this manner, working on liis knees, carefully avoiding to expose'^his body to view, until he has excavated 5 feet in length, and placed 3 gabions. ^ Sapper No 2, also on liis knees, works behind the first, and -widens his trench 20 inches. Sapper No. 3 follows the second, and deepens the excavation by 18 inches. The fourth Sapper widens the whole 10 inches to the depth of the third. The work pi'oceeds, the earth being thrown over tlie gabions, and two or three rows of fascines are placed on the top of these gabions to increase the height of the parapet. When the first sapper has filled two gabions and placed a third, they change places, the first taking the rear, and the other replacing the one iii front. The other four sappers of the brigade hand up materials to the working half, and every hour the half brigades relieve each other. Under ordinary circumstances a sap advances at the rate of 8 or 10 feet per hour. The sap is afterwards transformed into an ordinary trench by the working parties. (210). Another method, less ii-ksome but not quite so rapid, is also employed ; it is called the standing sap. The squad consists of three men. No. 1 leaves a berni of 18 inches, and digs a trench 18 inches wide and 3 feet deep. After Fig. 456. 236 DOUBLE SAP. having filled two gabions and loosened earth for a third, he goes to the rear ; No. 2 widens his trench 18 inches, and No. 3 widens No. 2's work 18 inches. (211). If the ajip roaches cannot any longer be made by zig-zags, (i. e., when 32 yards in advance cannot be gained by 100 yards of zig-zags), the besiegers must advance in straight line, which is done by means of a double sap. It consists of two single saps working side by side, so as to form a trench 10 feet wide at bottom, or only 6 feet, when there is no necessity for bringing guns through it. Each head of sap is covered by its sap roller, the interval between the two being protected by a third sap roller placed in rear of them. Instead of a sap roller, a mantlet, bidlet-proof, carried on small wheels, is some- times used, :uid in futiu-e sieges it will be necessary to adopt this method to cover the head of the sap. This sap cannot be carried forwai-d beyond a short distance, because it would be enfiladed by the defenders, who are enabled to see into it by the command of the place. In order to obviate this, returns are made by single sap at right angles to the double sap, so as to leave traverses at greater or less intervals' according to the i-equiroments of defilade. This sap, in ordinary circumstances, proceeds at the rate of 30 yards in twenty-four hours. DIRECT DOUBLE SAP. i'M FlO. 459. FlO. 460. The necessity of avoiding enfilade has caused the adoption of a serpctitine sap (fig. 461), but the frequent tiu-ns occasion delays, and therefore this sap is not recommended. Via. 461. Fio. 462. (212). Another sort of sap, due to Colonel Jebb, R. E., and called direct double sap (fig. 462), is now superseding the old methods, because it proceeds at a greater rate — 40 yards in twenty-four hours. The gabions of the right and left sap are placed 26 feet apart, the head of the whole space being covered by four or five sap rollers lashed together. A third squad works on between, placing its gabions as a third row in the centre, so as to give 1 2 feet clear on either side. At every interval of 12 feet or more, according to the requirements of defilade, this third squad makes a short sap alternately across, in order to constiiict a traverse. Other squads follow these to complete the work ; and the central row of gabions being removed, the two trenches of the right and left sap are united, forming a winding trench, with lock traverses. Besides the saving of time, this sap possesses the advantage of always going ahead, and of avoiding the tlifficulties of turning. (213). When the vertical fire of the defenders renders the passage of the saps dangei-ous, they are protected by dispositions similar to tlioso represented. (Fig. 463, 464). THIRD PARALLEL. Fio. 463. (214.) When the heads of the saps reach the foot of the glacis, they break into single saps on the right and left of each capital, to connect their work together, and form the tldrd parallel. This happens the ninth or tenth night. This parallel connects the heads of the attack, and gives to the besieger a secure position to collect materials, and prepare for further operations. As it does not extend on either flank much beyond the salients attacked, it is much shorter than the others ; but it is wider, usually, 24 feet, in order to receive a strong covering party, whose assistance may be in constant requisition, and to hold the great quantity of materials which is constantly wanted in the fui'ther advance. The parapet must therefore be higher, and this is done by placing two rows of largo fascines over the gabions. Some loopholes, formed with sand-bags, enable the besieger to keep up a brisk musketiy fire. Batteries of mortars and howitzers are also constructed when necessary, to CROWNING OF THE COA'EKED WAY. silence the fire of the covered vfay, and are usually placed on the capitals of the re-entering places of arms. During this period of the siege, 4 the guard of the trenches is placed in the third parallel, and } '" t^ie second. The besieger now approaches the momentous period of the siege. To enter 240 ATTACK OF VIVE FORCE. the place he must destroy or breach the escarp of the ravelin, and do the same (217) to the body of the place before Riving the assault. His battei-ies must be established in the parapet of the covered way, and to render their construction less dangerous, trenches are excavated to sink them. This sap is called the Crowning of the Covered Way. It is made either by regulai- or by flying sap. (215). When the covered way must be carried by open force (an operation only to be attempted in cases of great necessity, on account of its danger), the requisite gabions, fascines and sandbags are collected in the third parallel. Besides the usual guard of the trenches, and the workmen, 400 or 500 men per salient, are disposed on their rear. Tlie batteries open a brisk fire, and when they cease, suddenly, at a given signal, the men, clearing the parallels, rush to the covered way, desti'oy the palisades, and engage the defenders : as, in the meanwhile, the place ceases fii-ing to avoid injuring their own troops, the sappers dispose their gabions according to the direction of the engineers, at six yards from the crest, and begin the crowning, whilst others establish the communications with the parallel by means of a flying sap. This method is only resorted to when the garrison is not numerous. This crowning is very dangerous : it must be well preconcerted, to avoid con- fusion ; yet the great accumulation of men on the same point may prove fatal if the enemy can bring a gun to bear upon it. There is no doubt that the attack of the covered way is, after the assault, the most dangerous and difficult operation of a siege. Vauban pronounced himself very strongly against an attack of vive force : — " Of all the obstacles which the necessity of defence has invented to resist the attacks of the besieger, I know of none which has cost more trouble to surmount than the counterscarp, when it is defended ; for the first attempt, whether success- ful or unsuccessful, but more especially in the latter case, which is also of more common occurrence, is never made without great losses. I recollect that at Stenay, five successive attempts, which were attended with a loss of 500 men killed or wounded, were failures. There were three failures at Valenciennes, and yet the besiegers were not masters of the counterscarp when the siege was raised. The attack of the Marquis of Uxelles at Monlmedy in 1657, resulted in notliing; and in that of Mai-shal de la Ferte, from the first lodgment, which failed three times, to the last, which was as often unsuccessful, there was an interval of three months. I have heard it said that there were three failm-es at Dunkirk, and that at the last siege of Arras there were even as many as six or seven failures, in each case attended with great losses. Indeed, in sieges of places which make but a feeble defence, there are invariably three times as many men lost before the taking of the counterscarp as after ; and this always arises through a too great eagerness to hasten the operations, an eagerness so great that not half tlie TRENCH CAVAUERS. 241 necessary precautions for such a contest aro overtjiken, whicli, instead of advancing tlic operations one day, very often retards them two, and tliat too at the expense of tlie best troops, who, on such occasions, meet witii a wretched fate." To this it may be added that — in 1676, at Piiilipsburg, it cost tlio besiegers 1200 men; in 1695, at Namur, 3000 men; in 1702, at Kaiserwerth, 2500 men; in 1708, at Lille, 6000 men; in 1713, at Friburg, 1750 men. (216). When the attack on the covered way must be made systematically, the besieger advances from the third parallel in double sap, but when possible he avails himself of the slope of the glacis by opening two saps from the parallel, at about from 30 to 40 yards on each side of the capital ; and excavating in a cir- culai- way, so as to make the saps meet on the capital at about from 30 to 20 j-ards in front, he forms what is called the circular portions B, B, B. They aro not exposed to enfilade like the saps. From tho circulai* portions, the besieger advances by double sap to within 30 yards of the covered way, a little beyond the range of the grenades of the defenders. The two brigades part then and advance to the right and left along the sides of the glacis describing the head of a T, and push on to about 20 yards beyond the jirolongation of the crest of the covered way. The outer ends of these saps are transformed into Trench cavaliers, or high parapets formed of 3 or 4 tiers of gabions. They were employed for tho first time by Vauban, at the siege of Luxemburg, in 1684. They consist of two faces each about 10 yards long, inclined at from 100° to 120°, (fig. 467, 474,) the first commands the terreplein of the covered way ; the second, serves as a mask against enfilade and reverse fire, to look upon the places of arms of the bastions. The relief of these cavaliers must be such, that the shot may strike the foot of the first traverse and plunge along the other parts of the covered way. Marksmen posted on theif sides compel the besieged to give up this out- work. Then two squads of sappers, issuing from the extremities of the T, advance in double sap to the salients, and join at six yards fi'om them ; there they part again, to follow the crest on both sides at that same distance of six yards, 242 HALF-DOUBLE SAP. and the crowning proceeds. At tlie siege of Antwei*p (1832), the French did not consti-uct any cavaliers, but employed instead batteries of howitzers and mor- tars, a plan which it is necessary to adopt whenever the artillery of the garrison is not almost entirely silenced. (217). We have already seen that in polygons of many sides, the ravelins prevent the besiegers from advancing on the bastions, and that it is necessary to carry two ravefins before assaulting a bastion. This case Ave have not selected because we shall have an opportunity of explaining the process of attack against a modern fortress in which the ravelins have a great saliency. We suppose that the bastions and the ravelin can be assailed simultaneously, and we therefore represent in the diagram the works of the besieger against the ravelin as well as against the bastion, although in i-eality the assault of the ravelin may not take place, the enemy abandoning this outwork when the bastions are breached. (218). We are supposing the Trench cavaliers to have been completed on the 12th or 13th night, and the crowning of the covered way of the ravelin to have been begun on the 13th or 14th night. It is continued right and left, always leaving 6 yards parapet along the crest of the original glacis. Some traverses, constructed whenever necessary, will protect the besiegers from the enfilade and reverse fire of the bastions and collateral ravelins. The width of the trench is 12 feet, except at the points where batteries are to be constructed, in which points it is 24 feet; it is executed by a process called half-donble sap. The sap is carried on as a double sap, except that the gabions on the reverse side ai-e filled with sandbags, and when the traverses are completed, those gabions are removed. To prevent offensive returns in the salient places of arms, and to render dan- gerous the access of the defenders to the re-entering places of arms, a sap is often carried across the terreplein, to be transformed into a breastwoi'k for a few riflemen, who will fire across the ditch. At the same time saps are carried to the covered way of the bastions, so that on the 15th the re-entering places of arms are crowned. If, however, the gai-rison defends itself vigorously, the advance on the re-enter- ing places of arms might be attended with danger, in which case a fourth parallel is found necessary, and as it would mask the mortar batteries, these are Ijrought forward. (219). The same day, counter-batteries (2, 2, 2, fig. 4G6) and breaching batteries (1, 1, 1, fig. 466) are constructed, and a descent into the ditch begun. The counter-batteries at the salient of the covered way of the ravelin are intended to fire across the ditch to destroy the gmis that flank it on the faces of the bastions. They may be completed in 15 hours, and when the defence is silenced they may open a breach on the faces themselves. The counter-batteries METHOD OF MAKING A BREACH. 243 at tlio salients before the bastions are destined to silence the artillery of the flanks wliieh defend tlie main ditch. The brcachinj:i; batteries ai'e constructed opposite the point itself where the breach is to bo made. In order to protect the gunners, the embrasures are not cut entirely through : 3 feet of earth are left which are afterwards blown away by the first dischai-go ; and it is usual to cover the neck by a moveable door or some muskct-pruuf apron ; the second diagram represents a contrivance proposed by Albert Durer. (220). In order to make a breach, Vauban recommended cutting a horizontal gi'oove, and then firing by salvoes to bring down the masonry. Bousmard, (Chapter XXIII.) besides the horizontal groove, recommended two vertical ones, one at each extremity. The number of guns employed was at least 8, but since the experiments made at Metz in 1834, 1844, and at Bapeaume in 1847, it is admitted that four guns are sufficient, the 32-pounder or 24-pounder being most suitable. Filing at an angle less than 50° should be avoided, because the shots are liable to ricochet. The method actually recommended consists in firing at the escarp six feet from the bottom of the ditch, or at ^ of the revetment if the ditch is wet, so as to cut a horizontal groove through the masonry ; vertical grooves more or less distant according to the nature and strength of the revetments are similai'ly cut, but are not necessary with hollow revetments. The masonry is afterwards brought down by firing salvoes. To cut the gi'ooves, the charge should be J- the weight of the shot, whilst for the salvoes destined to produce a concussion, it should be 244 THE DESCENT INTO THE DITCH. reduced to -^ or i. The breach thus made is afterwards smoothed down to a slope of 45° by means of shells. The width should vary from 50 to 100 feet, to allow 25 or 50 men to mount abreast. When the breach is opened from a great distance, the quantity of metal is greatly increased, and the time required for the operation is prolonged. The results of the breaching operations at Badajoz, Ciudad Rodrigo, and San Sebastian, give the following mean : — At 575 yards, a breach of 100 feet was opened by 10 gims in 83 hours, making an average of 92 shots per running foot. At Antwerp, 6 guns opened a breach 80 feet wide, in 34 hours, from a distance of 55 yards, the number of shots being 16 per foot. The experiments of Metz, give a breach 74 feet wide in 8^^ hours, by 4 guns at 34 yards, firing 4 shots per running foot. Those of Bapeaume give a bi-each of 66 feet, opened from 34 yards by 4 guns, with 24-poimders in 3 hours 50 minutes, firing altogether 1 90 shots ; with 1 6-pounders in 4 hours, firing 285 shots; with 12-pounders in 4 hours 50 minutes, firing 380 shots. It may therefore be assumed, that under favourable circumstances, a breach can be made in 8 liours with 5 shots per running foot. (221). The descent into the ditch is a difficult operation, which often delays the besiegers. The breaching batteries are ready on the 15th, and the breaches may be made on the 16th night, but it is not until the 19th that the descent can be completed. To make this descent, the besieger sinks a shaft in his crowning, just opposite the breach ; and a gallery is driven (Chapter XVI. ) to the counterscarp. Sometimes the descent is begun from a boyau run up for the purpose. The slope of this gallery is regulated according to the height of the counterscarp, so as to arrive ^^WlpLTiJ 3 feet below the level of the ditch if dry, or 1 foot above the level of water if the ditch is wet. This slope should not be steeper than J , and if the ditch is deep, the shaft is sunk further off, in some zig-zag excavated for the purpose. This shaft is generally 10 feet square and at least 10 feet deep, in order to let 3 feet of earth remain untouched over the gallery. "The cUmensions of this gallery are G! feet high by 7^ feet. The side of the shaft opposite the gallery is sloped into a ramp and covered with blind frames, (as represented in figs. 472 and 473,) over which CROSdlNC; THE DITCH. 245 ■ • • ' -7^ Hf^4=v^ fascines and eartli are laid to resist shells. When the ditches are shallow, it is impossible to leave 3 feet of earth above the gallery, and consequently, the whole descent must bo blinded. It is necessary to make the descent opposite the breach, because the rubbish will give cover to the besiegers when crossing the ditch. It sometimes happens when the ditch is shallow, that a few shafts are sunk close to the counterscarp, and chai-ges are lodged in chambers at their bottom, the explo- sion bloios in the counterscarp, and the ruins join those of the breach, forming a ramp leading into the ditch. (222). When the descent is completed, and when a reconnoissance has ascertained that the breach is practicable, the revetment of the counterscarp is cut through, and a sap is carried across the ditch to the foot of the breach. If the ditch is wet and the water stagnant, a causeway is formed across by means of fascines loaded with stones to make them sink, and an epaulment is raised on it. When the water is running, and when the garrison has the power of filling and em[)tying the ditch at pleasure, the passage of the ditch becomes an operation of the utmost difficulty. In this case, if a dam cannot be made with fascines and sandbags to sujjport the weight of water until it is allowed to run out through other chamiels, a bridge of some sort must be made. The small pontoon-bridge of Colonel Blanchard is recommended (167). The cask bridge of General Pasley has been proposed : casks, with their ends removed, are fixed together in sets of four. Each set is launched in the direction of the current, and is made to sink by means of sandbags : several sets are sunk until the upper ones appear on the surface, forming a flooring for the fascines. Another method, employed at Philipsburg, in 1734, consists in the construction of a floating bridge of fascines : these ai-e laid alternately crossing each other at right angles, with hurdles between, and fixed together with pickets. Sandbags sink the bridge to the level of water to prevent the defenders from setting fire to it. The epaulment is constructed considerably within the edge, and fresh raw hides cover the whole. If the current is strong, the bridge is kept in its place by anchors cast up the stream, and by props driven below. THE ASSAULT. Under ordinary circumstances, the operations of the siege are completed on the 19th niglit, and the assault is given at daybreak. (223). This assault on the bastion is the most important operation of the siege; it is for it that all others have been made, and so many lives have been sacrificed. When all is ready for its execution, the general entrusted with its command ascertains that all the communications of trenches, descents, galleries, &c., are in good condition. The breaches are reconnoitred, and dispositions are carefully taken to avoid confiision ; the strength of the column of assault, of the reserves, and of the working party, is determined. A little before the appointed time, the enfilade batteries and those of the covered way, keep up a vigorous cannonade, and once the signal given, the columns, eight or ten files in front, issue from the trenches, run across the ditch, and assault with fixed bayonets the defenders of the breaches. It is advisable to postpone this decisive movement till daybreak. After a success, great care is still necessary ; pursuit must not bo thought of, lest some ambuscade should have been prepared, and great circumspection must be shown in taking jjossession of the ramparts and of the town. During the assault, A LODGMENT. 247 the army is under arms, ready to prevent the garrison from making its escape, or to repel any atteni[)t to relieve the place. It should be borne in mind that the success of an assault gi-eatly depends on the good order preserved among the troops, and that it is a fatal mistake to entrust the duty of an assault to detachments. The troops should be employed as organized with their own officers and non-commissioned officers. When the assault is given to an outwork, or to a bastion containing interior retrenchments, it is necessary for the besieger to construct rapidly an intrench- ment, generally a trench, on the captured breach, in order to maintain the position against recapture. This lodgment, as it is termed, can be made in two ways : either by a working party, which places the gabions on the breach whilst the storming party is fighting, or by a regular sap advancing from the ditch up the breach: in tliis method, which is recommended by Vauban, the breaching batteries are ready to open fire on the breach, should the gairison retmii to dis- lodge the sappers. 248 CHAPTER XIV. DEFENCE OF A FOKTRESS. (224). When a garrison receives information of the intention of the enemy to lay siege to the place, it at once proceeds to prepare the means of resistance. The ditches in front of the place are filled, and the houses, walls, hedges, trees, &c., and all the agricultural buildings, levelled. Sometimes subm-bs are intrenched, when they are likely to check the advance of the enemy. The banquettes and interior slopes, ramps, &c., are repaired, platforms and traverses for guns are constructed, palisades are placed all along tlie banquette of the covered way, and the passages of traverses and sallyports shut with barriers : if possible, a second row of palisades is planted in the terreplein of the covered way. At the same time, advanced posts are pushed forward on every road as far as prudence will jjermit, and their picquets and vedettes will prevent a surprise: they will be sufficiently strong to obstruct the investment and secure the arrival of convoys and reinforcements ; their retreat shoidd be seciu-ed ; and signals should be provided, so as to i-eceive intelligence from the neighbouring country. All provisions and materials likely to be of use for the defence should be brought in or destroyed. When the advance ports are driven in, guns should be in readiness to fire from the salients of the covered way, and small detachments should be concealed in broken ground or ruined buildmgs, keeping themselves within the covered way at night, and during the day advancing a few hundred yards, they shonld endeavour to surprise the reconnoitring parties. The officers of artillery at the same' time ascertain the range of the guns as compared with the distances of the surrounding objects, if it has not been done before. At the same time tools and implements are collected, at the rate, for 1000 men, of 100 axes, 200 hatchets, 150 wheel-barrows, 10,000 sandbags, 200 chevaux-de- frise, &c. ; wood is stored for stockades, galleries, mines, &c. At least 500 gabions, 2000 fascines, 600 hurdles, &.C., are prepared for revetments. DEFENCE OF A FORTRESS. 24'.! (225). WIteti the investment is completed, tho dei'enders endeavour to aseertaiii on which front the attack is intended to be made, in order to delay the opening of the trendies : should they discover the time and i)lace of the opening, as soon as the besieger begins, all the barbette batteries, and as many guns, howitzers, and mortars as can bo brought to bear shoidd keep up a vigorous fire ; but when the parallel is completed, the firing should cease, as it would be a waste of ammunition. Sorties of light troops are now made to impede the workmen, but at this period of the siege there is need of great caution: sorties should be made at several points agamst the works, and if they can reach tho pai-allel, the working parties that accompany them will soon destroy one night's progress. As a general rule, sorties should only be made in force for the purpose of destroying a battery or a work which causes much hai-m to the defence. The next caro of the defence is to prepare the batteries of the fi'ont of attack, and erect traverses 18 feet thick between every two guns. The positions destined for the enfilade and ricochet batteries of the besieger are easily known, and as many hea\y guns, and more especially heavy niortai-s as can be spared, should bo kept ready to concentrate their fire on each battery in succession, it being a fact well known at present that no battery can resist a well-directed fire from shells. Embrasures are also cut through the parapets of collateral fronts having any view on the attack, and the guns are mounted only when wanted, so as to avoid unnecessaiy exposure. (226). After the besieger's batteries are erected and armed, the defence will reserve its fire for a later period, and chiefly check their progress by musketry. It is also during tho same period that fleches and counter approaches are made outside, and retrenchments and blindages consti-ucted inside the place. Fleches ai"e small redans of faces, from 20 to 40 yards in length, rapidly thrown up in the capital, at the foot of the glacis ; their terreplein is generally sunken, and they derive support from the works in rear or from other fleches. Lines of counter approach, a sort of trench or sap, are excavated in front of the glacis, to be connected with batteries hastily thrown up on positions where the zig-zags can be enfiladed ; they generally debouch from the covered way of tho ravelin, collateral to those attacked. The establishment of the Russian rifle-pits, and the erection of their works on the Mamelon, in February, 1855, are instances of what a determined garrison can do to impede the progress of the besiegers. The retrenchments in bastions are generally a pennancnt construction (chap. XX.) but when none exist on the front attacked, the garrison should organize such works as time will permit, either a trench across the gorge of ravelins and bastions, or a gabiounade, a stockade, or a palisade. As for the blindages, they require especial care ; they are bomb-proof slielters for the troops, guns, magazines, cisterns, hospitals, &c. When the barracks, magazines, &c., have not been built shell-proof, the best thing to do is to demolish the upper stories, and cover the first floor with two courses of joists close together, and crossing each other, and to put over it 4 or 5 feet of earth. Under the beams of this floor, girders, some 1 2 inches square, are - SCOQ£2!VS5SSZB:v3DiJ 7 1 J 4 ' I placed 10 feet apart, and are supported by vertical posts as well as by the walls into which they are inserted. The windows and door-ways are protected by inclined beams ; and whenever there is a doubt as to the strength of the walls, they are blinded by inclined beams covered with earth, or supported inside by props. Should there be no building fit to be blinded, the defenders construct a leaning blindage behind some strong wall or behind some coimterscarp, the timbers of which being square, are inclined at 60°. They rest on a sleeper, are fastened by joists, and are covered with earth. Fig. 476. Or a double blindage is constructed, cither in the form of an inversed V, or by Fio. 477. Fio. 478. DEFENCE OF A FORTRESS. 251 some construction undei* a traverse, or even by covering the space between two traverses with beams and earth. Tlio guns near tlie salients of the ravelin and tlio bastion are generally blinded, and the besieger will have great trouble to silence them. Such blindages are constructed with sti-ong posts, 1 foot square and 7 feet high, placed vertically on both sides of the platforms, and supporting a roof of beams covered with fascines, and 4 or 5 feefc of earth. The sides exposed to enfilade are protected by thick mounds of earth. • (227). After the completion of the second parallel, the chief effort of the defence must be to direct such a fire of musketry on the approach as will prevent the besiegers from using the flying sap : loopholes with sandbags are constructed on the parapets for riflemen ; and if a field gun can be brought to bear on the head of the saps, the latter will be much retarded. The guns ricochet along the capitals with shot and shells. Some mortars placed at the salients of the covered way will fire stones, and as many mortars as possible will fire shells and grenades into the trenches. The sorties become more and more active ; they ai-e directed against the head of the sap, and endeavom- to interrupt the consti'uction of the thii'd parallel. W/ien this is finished, the gan-ison must expect an attack on the covered way, and prepare for it; it is recommended not to await the besiegers in the salient places of arms, but to retire to the re-entering places, after having given tliem a volley, thureliy unmasking the covered way to the fii-c of the works in rear. 252 DEFENCE OF A PORTRESS. Sorties are prepared in these re-entering places in case the assailants should waver. If the covered way is attacked by the i-egular process, tlie advance is checked by the vertical and musketry fire, by blinded batteries erected in collateral salients, and even by guns not seen by the attack, and firing at ricochet in the direction of the prolongations of the trenches. Riflemen continue their fire. (228). After the crowninfj of the covered way, the defence will lose no oppor- tunity of impeding the construction of the counter and breaching batteries ; shells are fired into their parapets, and marksmen pick ofl" the gunners. The batteries or the flanks are blinded, and a vigorous vertical fire is kept up on the entrance of the descent into the ditch. The collateral flanks contribute their fire. Sorties are made into the ditch to resist its passage, and all the fire of musketry and artillery that can be had is directed against this part. Should the ditch be pro- vided with sluices for filling or emptying at pleasure, the advance of the besiegers may be cheeked for a time : the garrison first defends the ditch when dry, and when the enemy reaches the foot of the breach, water is let in, and left there until the besieger has again crossed, when the ditch is suddenly laid dry. If the ditch is permanently wet, the defence will throw combustible matter, shells, &c., on the dams of fascines. (229). The breach at last is practicable, and the flanks are silenced, and the only resource left to the garrison is vigorously to defend the breaches ; there all its energy is called into play ; fires are lighted on their slopes, and kept bm-ning by a continual supply of fascines, &c. At night, quantities of crows' feet and broken glass are spread ; chevaux-de-frise, abattis, &c., are placed, and barrels of powder and shells are duly prepared to be lighted and rolled on the columns of assault when they reach the foot of the breach : fougasses are also prepared, and any means that the garrison can dispose of. There are instances of breaches being defended by fixing on them planks rendered slippery with soap, and of assaulting columns being repulsed by the fall of several bee-hives amidst their ranks. If these means prove insufficient, and if no gun has been saved on the flanks, the last resource consists in selecting the most resolute men to charge the assailants. These troops are, if possible, covered with cuirasses. The first rank, armed with long pikes, kneels, whilst the rear rank pours a volley on the enemy ; grenades, &c., being thrown upon both sides of the breach by special detachments. Then they charge with fixed bayonets, and the reserve comes to their support. If driven back and pursued actively, field artillei-y, kept in readiness, may still check the advance of the besieger. The defence of the breaches is one of the most important — not to say the chief resource, of a besieged fortress ; and a garrison sliould never give way to dis- DEFENCE OF A FORTRESS. 2r,ii couragemcnt because the ramparts have been battered clown; it will still fight at a (jrcat advantage, and there are many instances to be found in military history of a successful resistance. The defence of Rhodes in 1521, besieged by Solyman, shows what a small but determined garrison can do against a much sujjerior foe. When the Constable of Boui-bon had mined the ramparts of Marseilles in 1544, tlie breaches were so skilfully and gallantly defended, that the Imperialists wore compelled to raise the siege. At ^laestricht, in 1G76, a French garrison of 6000 men fought so vigorously for the defence of the breaches, that the Prince of Orange was obliged to give up any further attempt, and to retire with a loss of 12,000 men. The breaches of Turin (1706) were defended by large fires — and success- fiilly, too. St. Jean d'Aere was besieged in 1799 by Napoleon, and although the ramparts had been overthrown, all assaults proved misuccessful, and the French had to retire, leaving their giuis behind them. In many other instances the Turks have given us a good example to follow, especially in the Russian campaign of 1828. At Badajoz, in 1811, the English were repulsed at every assault. In 1812, the same place again resisted, and if General Picton had not surprised the Castle of San Cristoval, the vigorous defence of the breaches would again have saved the place. Even when the besiegers have gained a footing in a foi-tress, all hope of further resistance is not lost. Prince Eugene, at Cremona, was obliged to retreat; so were the English at Bcrg-op-Zoom. At Saragossa, in 1809, the French had to besiege almost every house. The governor of a place cannot capitulate before having resisted at least one assault on the bastion. His honour is at stake. Want of arms and ammunition, or almost complete destruction of the garrison, are the only reasons that should induce him to surrender. The task and responsibility are immense, and none but men of great skill and energy are fit for that post. To prolong the resistance at all risks must be his motto. When all fails, then he must endeavoiu- to obtain good terms, and if they are refused, his forlorn hope is to attempt an evacuation, and to force his way through the investment. (230). Ever since the middle of the last century, it has been considered advisable that the governor of a besieged fortress should keep a "journal of siege." This journal contains the names and grades of all the ofiicers who command the besieging army in addition to those of the garrison, those of the regiments or their distinctive numbers, &c. It is divided into two columns : one for the attack, the other for the defence. 254 DEFENCE OF A FORTRESS. All tlie operations and events are recorded day by day : the number of working- parties, the time of execution, nature and purpose of the works ; the numbers of wounded and killed, the names of the men who distinguish themselves, &c. These joui-nals are excellent guides for the study of the science : by means of them we can ascertain the time necessary for the execution of the parallels, batteries, mines, &c., and form bases from which to calculate the probable duration of the siege of a fortress, the quantity of ammunition that will probably be required, &c. CHAPTER XV. FORCES E^rPLOYED IN A SIEGE. (231). The armament of fortresses depends much on the size of the works and on tlio locality in which they stand, and no fixed rule has been adopted to compute the amount of ordnance necessary for the defence. Vauban wanted 10 guns per bastion, and 5 mortars or pierriers, making 90 pieces for a hexagon. Cormon- taingne fixed a minimum of 36 and a maximum of 46 for the same polygon. In France they now divide their fortresses into three classes, and allot 110 pieces for the 1st class (10 fi-onts or more) ; 70 for the 2nd class (7 to 10 fronts) ; 30 for the 3rd class (4 to 6 sides). This ai-mament is independent of 10 pieces per bastion, which are intended to provide for the immediate security of the place. At this rate, a hexagon would require 90 pieces. Of this ordnance 54 per cent, are guns, 26 per cent, howitzers, and 20 per cent, mortars. In tliis country, the best authorities calculate the armament at the rate of 8 pieces for the immediate security, and 150 pieces for a jilace of 10 fronts or upwai-ds, 100 for a place of 6 to 10 fronts, and 50 pieces for a place of 4 or 5 sides. The hexagon would thus require 148 pieces. Some authors fix the proportion of the several natures of ordnance at 50 per. cent, of heavy guns; 10 per cent, howitzers; 30 per cent, mortars, 10 per cent, field guns ; but it is generally admitted that a greater percentage of howitzers is necessary, because shells do more against earthworks than solid shots. The best ordnance for the defence of a forti'ess are for solid shot : the two kinds of 68-pounders, the 32-pomiders of 58, 56, and 50 cwt. respectively, and the 24- pounders of 50 cwt. ; for shells, the 10-inch shell gun, the four kinds of 8-inch fiuns, the lO-inch howitzer, the 8-inch howitzer, and the 32-pounder of 25 cwt. Of mortars the best are the 13^, 10, and 8-inch. The small brass mortars of 5| and 4|-inch, are recommended for firing on the working parties of the besieger. There are generally in fortresses wooden standing garrison carriages, but any carriage will answer the pur[)ose, and about one-third as many more should be 256 GARRISON. kept in store to replace those that may be destroyed. The platforms, wood or stone, are usually on the ground, except at the salients, where low traversing platforms are necessary. For the transport of this ordnance, sling carts or sling wagons for the guns, and trench carts for the mortars are provided. Gyns and sheers are also necessary. (232). With regard to the ammunition, the quantity required depends on the duration of the siege; it is therefore very variable. However, it is usual to reckon 700 rounds for each gun, and 500 for each mortar of a 1st class fortress ; 600 and 400 for those of a 2nd class ; and 500 and 300 for those of a 3rd class. In addition to these there should be a certain quantity of shrapnel shells for the guns, and of light balls and poiuid shot for the mortars. (233). To compute the strength of the garrison, it is usual to divide the troops into thirds, one third on the front of attack, one third at bivouac and ready at a moment's notice, and one third at rest, although towards the latter period of the siege the whole gai-rison is constantly required on the ramparts. A place can always be defended, whatever be its garrison, yet as a force too numerous would prove a great inconvenience in a fortress, it is advisable to find a minimmn: troops which can be more usefully employed in the field will not thus be wasted. The calculation for a hexagon will give an idea of the principle. When the enemy arrives before the place, the garrison has no other duty than that of putting the place into a state of defence, and sending out patrols and recon- noitring parties ; nor will its service become heavy until the besieger has begun sapping. Now it has been shown by experience that if 60 shots are fired per minute on the head of an attack, tlie besieger must have recourse to sapping : for the 3 salients we require in the covered way 180 men, but as they cannot fire constantly, we i-eckon three times that number, or 540. The ravelin of attack requires 150 men. For the repairs of parapets, &c., we must allow 100 men, and as many more for the fatigue pai'ty helping the gunners. For the fronts not exposed to attack, sentries are necessary, and 100 men to contribute to the various posts are not too many. Adding 100 men for the collateral fronts, this will make altogether 1090 in- fantry, and for the three reliefs 3270. Giving 300 for artillery, 120 for enghieers and staff, and 80 for cavalry, the garrison will amount to 3770 men, a little more than 600 men per bastion. As a rule, therefore, we can fix the garrison of a square, pentagon or hexagon, at 4000 men. Vauban required 600 infantry per bastion, plus 60 cavalry, and 100 for staff, artillery, and engineers, altogether 4560 for a hexagon. Cormontaingne demanded very nearly the same number, 4100. For the security of a place 440 men per bastion (of which 350 infantry, 10 STORES. 257 cavalry, 60 artillery, and 20 engineers) are sufficient. For polygons of more than 6 siiles, the garrisoa for tlie defence is reckoned at 440 per bastion, and double that number for the fronts susceptible of attack. Great support from the inhabitants cannot be expected ; only one-sixth of them are fit for service, and one-eighteenth only can be employed at a time. The maxi- mum of a gaiTison is determined by the capacity of tlio barracks, casemates, &c., and by the amount of provisions. A representing the number of rations, and B A the strength of the garrison,— must be greater than the usual length of a siege. (234). The stores for the garrison, including anmiunition for musketry, tools, provisions, &c., are placed in magazines for which bombproof shelter should bo prcpai-ed. It is customary to provide surplus arms at the rate of one for every 4 men ; wall pieces 10 jier bastion, musket-ball ammunition 500 per man ; hand grenades 10 ditto; gunpowder in barrels 2-Llbs. per man, lead lOlbs. ditto; cart- ridge paper 1] quires. Besides the engineer and artillery stores, felling axes, bill hooks, pickaxes, shovels, and hand saws are provided, at the rate of one of each for 16 men. Although the governor of a fortress threatened with a siege warns the inhabi- tants to store up provisions, most of them are unable to maintain themselves, and the government has to distribute rations to them as well as to the gan-ison. The Aide Memoire for military sciences gives the quantity and the bulk of the pro- visions necessary for a siege of 56 days per 100 men. Cubic feet Cubic fe Flour or meal 22001bs. 76 Cocoa . 7001bs. 41 Biscuit . 56001bs. 3.58 Soft sugar 5251bs. 14 Salted beef . 5f>001bs. 216 Spirits 1400 pints 56 or pork . 5600Ibs. 202 or wine 5600 pints 224 Rice . . . 22001bs. 70 Vinegar 200 pints 8 or peas . 1400 pints 54 % Tlie fuel for cooking, Wood . 1200 Cubic feet. or coals, 7 tons . 350 J" or turf . 3000 „ Oil, 40 Gallons 4 „ Candles, 401bs. 3 „ Forage for 20 horses, Hay, 7 tons . . 4000 „ Barley, 72001bs. . IGO ,, or O&ts, 72001bs. . 250 Straw as liay, 7 tons . 4000 (235). The force of a hesietjing an ny deiiends upon the strength of tl 258 THE FORCE OF A BESIEGING ARMY. garrison, the morale of both armies, and the season of the year — elements which cannot form the basis of exact calculations. In some instances two armies are necessary ; one of observation to cover the siege, and prevent any attempt on the part of the enemy to relieve ; tlio other to besiege. To this latter army alone we shall direct our attention. It must provide men for the excavation and guard of the trenches, the construc- tion of batteries, and the uivestment of the whole cii'cumference of the place ; for the police of the camp, the outposts, patrols, extra duties, &c. ; also a proper number of sappers and miners, gunners, &c. Supposing the attack to be directed against a front of a hexagon, the first parallel and its commmiication on the rear occupying a development of nearly 6000 yards would i-equire 3000 men, but during the first night not niore than 4800 yards are excavated, and 2400 men are sufficient, and this number will remain the same till the opening of the second parallel ; as its development is less, fewer men will be wanted. Towards the latter part of the siege the number will still decrease, so that in general we may compute the working party at 2000 men. In order that the siege may be conducted with energy let us allow four reliefs, and we must then have 8000 men. The posts for the investment are at 3000 yards from the salients of the place, and as these are already at 500 yards from the centre, there is for the hexagon a perimeter of 21,000 yards; subtracting BOOO 3-ards for the first parallel, the investment must oecuj)y 15,000 yards, which at the rate of 200 men per thousand yards, give 3000 men. The guard of the trenches amounting to ^ of the garrison, makes 3000 men for a garrison of 4000 men, and at three reliefs it implies 9000 men in all. Adding to those 2000 men for four reliefs of fatigue parties, allowing 3000 for artillery, 300 engineers, 600 cavahy, the total force will amount to 25,900 men or more than six times the gai'rison. When the garrison is stronger, the guard of the trenches is the only item in the above calculation that will require to be increased, and the whole of the besieger's force need not be increased in proportion to that of the garrison. It is admitted now that for a garrison of 15,000 men, the besieging army should bo five times larger, six times for 10,000, seven times for 5000, and eight times for 3000. Although it is a difficult matter to fix any limit to the force of a besieging army when it has to prepare against the diversions of an enemy, yet it may be said that attempts with a force less than 60,000 men are not likely to prove successful. In 1793, the King of Prussia required 100,000 to besiege Mayence. The same year, the English and Austrians had 120,000 men before Valenciennes ; and the Prince of Coburg besieged Le Quesnoy with 60,000 ; but the Duke of York could not invest Dunkirk and Bergues with 50,000. BATTERINX; TRAIN. 259 It is trne that in 1796 Bonaparte invested Mantua with 20,000 men, half of which were employed in the siege; and that at Saragossa, in 1809, the French had but 35,000 men ; but again, at Silistria, in 1854, the Russians had 70,000 men. (236). The state, ai-mament and force of the garrison of a fortress, and the facilities of transport oftered by the country in which the siege is carried, will exercise a great influence on the selection of the kind of ordnance and of the force of the batterimj train. Different numbers have at various times been fixed. Thus — Vauban required 160 pieces, of which 70 percent were guns, 15 per cent howitzers, 15 per cent, pierriers; Bousmard required 168 pieces, of which 50 per cent were gims, 18 per cent howitzers, 22 per cent mortars, 10 per cent pier- I'iers; Gassendi required 160 pieces, of which 62 per cent were giius, 15 per cent howitzers, 15 per cent mortars, 8 per cent pierriers. A committee of artillery in 1819, recommended for the siege of a first-class foi-tress 140 pieces, i.e. 60 guns, 15 howitzers, 25 mortars, and 40 small brass mortars. Sir John Jones demanded 106 pieces : 40 gims, 20 howitzers, and 46 mortars. The regular battering train of Austria includes 178 pieces, of which 45 per cent are guns, 13 per cent howitzers, 35 per cent mortars, 7 per cent pierriers. That of Prussia 142 pieces, 60 per cent guns, 15 per cent howitzers, 20 per cent mortars, and 5 per cent pierriers. In France, previous to 1656, the number of pieces was 162; it is now 175,t]ms divided: 80 gims, 40 howitzers, and 55 mortars. In England, the maximum equipment is generally admitted to be 160 pieces, of which 60 are guns, 40 howitzers, 20 mortars, and 40 small brass mortars. For a fortress of 2nd, 3rd, or 4th class, this number is reduced. Some officers, instead of dividing this maximum, prefer to adopt a minimum of 40 pieces, and to double, triple, or quadraple it. The proportion recommended is : guns a, how- itzers, or shell guns i, mortars a, besides an equal number of small brass guns. General Burgoyne considers 25 pieces the minimum battering train for the reduc- tion efforts, and it may be added that no serious attempt should lie made against a front with less than 60 pieces. Until the adoption of rifled guns alters the actual composition of the equipment, the best ordnance is the 32-pounder of 50 cwt. which has superseded the 24-pounder since the Crimean war, the 8 inch shell gun which also proved better than the 10 inch, and 8 inch howitzers hitherto employed, and the 10 inch and 8 inch iron mortars. ^ It is understood that each gun has its carriage, each mortar its bed, and tliat J^ extra mountings are allowed for losses : sling and platform-waggons for 260 BA'ITEKING TRAIN. transport of ordnance, Flanders waggons, trench and hand carts for the con- veyance of ammunition and store; triangle gyns, &c., are also included in the equipment. As for the number of men necessary for that artillery, it is usual to compute it at 2700, and at 2975 including extra hands for laboratory, casualties, &c. During the reign of Louis XIV., the battermg trains were more numerous than in the wars at the beginning of this century. At the siege of Namiu- (1692) the besiegers liad 260 guns; at Charleroy (1693), 210; at Turin (1706), 251; at Menin(1706), 116; at Lille (1708), 200; at Douai (1710), 368. The following table of some remarkable sieges compiled from the French Aide- Memoire, will give an idea of the amount of artillery emjjloyed in modern times. Defence. Attack. Defence. Attack 1793 Valenciennes ... 175 167 1810 Tortosa ... 177 50 1794 Neuss ... 200 40 1811 Tarragona ... ... 290 66 1806 Gaeta ... 171 109 1811 Badajoz ... 170 54 1807 Breslaii ... 300 38 1812 Ciudad Eodrigo ... 119 68 1807 Schweidnitz ... 2,50 43 1812 Badajoz ... 140 78 1808 Eosas ... .58 53 1813 San Sebastian 03 88 1808 Girona ... 1G8 71 1828 Vania ... 100 45 1810 Lerida ... 110 40 1829 Silistria ... 238 88 1810 Ciudad Rodrigo ... 8G 50 1832 Antwerp .. 145 148 ISIO Almeida ... 98 67 (237). With regard to the amoimt of ammunition, the number of rounds per piece should not exceed that which is calculated to render it unserviceable : 1500 rounds per gun, exclusive of case, shrapnel and carcasse, is the utmost that may be reckoned. The following proportion for a battering train of a hundi'ed pieces, is given as a fair allowance. For a 32-pounder, 1000 round shots, 100 common shells,. 50 slirapnels, 50 grape or canister. For an 8 inch gun, 200 hollow .shots, 600 common shells, 50 shrapnels, and 50 grape or canister. For a 10 inch mortar, 600 common shells, 50 povmd .shot, 10 carcasses; small brass mortars, 300 common shells. The quantity of ammunition provided for a siege, and the amount actually consumed, vary widely, the place itself often providing the besieger with shot, as at Tarragona, where V of the projectiles came from the dei'enders. In the annexed table, we give the number of rounds calculated at the rate fixed above, and compare it with that of the rounds actually fired. BATTERING TRAIN. 261 Gacta (1806) . 100 pieces (84,500), fir ed 68,700 in 11 days Girona (1808) . 71 , (45,995) , 99,900 in 104 „ Lerida (1810) . 40 , (33,800) 9000 in 15 „ Ciudad Rodrigo (1810) 50 , , (42,250) , 17,901 in 16 „ Almeida (1810) G7 , , (5G,G15) , 10,000 in 12 „ Tarragona (1811) C6 , (55,770) , 42,000 in 28 „ Badajoz (1812) . 78 (65,910) , 35,346 in 11 „ San Sebastian (1813) 88 (74,360) , 70,831 in 36 „ Antwerp (1832) 148 , , (125,060) , 64,392 in 19 „ CHAPTER XVI. MILITARY MINING. SECTION I. -Mines. (238). A military mine is a subterranean excavation in wliich a charge of powder is deposited, for the piir])Osc of blowing up the enemy's troops or works, or of destroj-ing abandoned woi-ks to prevent tlie enemy making use of them. Offensive mines, or simply mines, are those executed by the besieger, and counter- 7nines those by the besieged. Before the invention of gunpowder, mines were excavations or galleries under the walls of a fortress ; the foundations were supported by props, and when completed, the excavation was filled with dry wood, and the timber set fire to. The props being burnt, the walls gave way and opened a breach. The defenders also excavated counter-mines to overthrow the machines of the besieger, and to prevent him from executing his mines. Powder was first employed for this purpose in 1503, by Peter NavaiTO, at the siege of the Castel del Uovo, at Naples. The excavations, when vertical, are called shafts ; when horizontal, galleries or branches, according to their size, (239). Shafts are generally rectangular, 3 feet by 4 ; but sometimes elliptical. Branches are from 2}r to 3 feet wide, and from 3| to 4 feet high. Small galleries ai-e 3 feet wide and 44- high ; gi-eat gallei'ies 6 feet 6 inches wide, and 7 feet 6 inches high. (240). The best soils for mining are those consisting of chalk, and also those of fine sand when cemented by clay or earthy matter. Clayey soils are the worst. When excavating in favourable soil, or in ordinary soil, at a small depth, the shaft requires no wood support, and is best made elliptical ; the galleries can be excavated either in rectangular form, or in that of an arch if they are intended to stand for any considerable time. FIIAMES Fio. 480. D To prevent mines excavated in had soils from falling in, the earth should be supported either by wooden frames or by cases, which are readily made from the floor of any house. (241). Frames are composed of four pieces, two long and two short; the long ones are of the same section throughout, but the short ones are notched at each end, so as to form shoulders for the long pieces, and to prevent them from parting ; tenons and mortises are cut near the ends of the pieces. They are made of scantling 3 by 4^ inches. Frames for galleries and branches are composed of two upright pieces called stanchions, and one top piece, called capsill ; the stanchions are usually let into the ground a few inches, and the capsill is placed over them, its mortises receiving the tenons of the stanchions. The stanchions are 4 inches square for branches, 5 inches for common galleries, and from 6 to 7 inches for great galleries, the capsill having the same width, but a depth greater by ^ or |. 264 sHAFr-SlNKING. Besides these frames, it is necessary to have one for the top ; the dimensions in the clear are the same, but the ends of the long pieces project one foot each way. They are fixed by tenons and mortises, as represented in the diagram; the same material may be used as with the common frames, but the position is reversed, because in the top frame the depth should be greater than the widtii. Together with these frames, sheetings or planks are employed 1 or l^ inch thick for the shafts or the sides of the galleries, and 2 or 2^ inches for the top of the galleries. (242). To sink a shaft, a pit, somewhat wider than the dimensions intended to be preserved, is cut vertically down to the depth of 2 or 3 feet, when a top frame is placed over it, its projecting ends buried to their own depth in the ground. The excavation is then continueil to 4 feet, when a second frame is placed horizontally at the bottom, having its sides vertically under those of the first ; and the sheetings are let down between the sides of the pit, and the exterior of both frames. In general, two planks are sufficient even in soil of ordinary tenacity ; they are pressed home close to the top frame, and at the lower one they are kept out by wedges. The two frames are fastened together by four braces of wood, or by means of ropes. /tv c\,c^ ^a^^< ' 2(.)5 Ki o. 48 >. 11 - — — ' 'i ; ^=1 fc J 1 t ] J 3= 1 i The excavation is then continued to 4 feet, when another frame is placed at the bottom, and tlie wedges being removed, the planks are let in between the first set and the frame. The work proceeds in this manner until the last frame is placed at about 9 or 12 inches above the level of the capsill of the intended gallery, and the excavation is continued down to the level of the bottom of the gallery, tlireo sides only being now sheeted. When the shaft is sunk with a view to commence a gallery, care is taken that the sides of the top frame agree with the sides of the proposed gallery. (243). Tlie galleri/ is excavated in a similar manner, the first frame being carefully fixed on the sides of the shaft, and the direction of tlie centre of the gallery being marked by two pickets, which afterwards serve to dress it FiQ. 486. Fio. 487. \r In great galleries, or in all galleries in bad soil, sleepers or ground sills are laid beneath the ends of each of the frames, to prevent the stanchions from sinking unequally ; they are buried to their own depth. (244). When a gallery is required to incline downwards, instead of sinking a shaft, it is preferable to commence it fi-om behind a cover, the parapet of a sap for instance. The trencli is deepened so as to allow 3 feet of earth above the top of the gallery, and the direction being marked by two pickets, the first frame is placed, leaning forward in a direction perpendicidar to the descent. The work proceeds as in the general case, the distance between the stanchions being measured along the slope, and not horizontally, in order to use the same sheetings. (245). In changing the inclined direction of a gallery to a horizontal course, the first vertical frame must be supported by struts parallel to the stanchions of the last oblique frame, because the weight of the earth tends to overset the frames. Fig. 490. BKANCHES. 2G7 (246). The branches are executed in the same manner, except that the stanchions need not be inserted so deep into tlie ground. An oblique frame of larger dimension is generally used and dressed with the side of the gallery. (247). When the soil is not favoiu-able, the sides of the shaft and galleries shoidd be entirely sheeted ; when the soil is very bad, the miners make use of false frames, or frames of the usual height, but narrower, and exactly of a width from outside to outside, equal to the width in the clear of the ordinary frames. As soon as the excavation is carried one or two feet beyond a regular frame, the top sheeting is introduced, and the false frame placed in the same manner as a common one ; the miners having excavated a little further, push on the false frame, 268 CASES. never allowing the top sheeting to project more than sis inches beyond it. To avoid wedging the sheeting, the false frame is made 2 inches higher, thereby giving an upwai-d splay to the planks. (248). The method of mining with frames is now superseded by the method of casing, because it produces a larger gallery or shaft by means of a smaller excavation, involves no trouble of measui-ing, plumbing, or levelling, requires no false frame in bad soil, no sheeting, no brace or rope to fasten the shaft's frames, and especially because it enables the work to proceed much more rapidly, and allows of its being carried on without danger in soils quite unfit to be worked with fi-ames. (249). A case consists of four pieces of two-inch planks, two side pieces or stanchions, and two end pieces or cap, and ground sills, fixed by tenons and mortises 2 inches long, and 3 inches wide. A couple of i-ivets prevents them from splitting. The planks are 1 1 inches wide. For great galleries more strength is required, and tlio ground sills are 3 inches, the stanchions 4 inches, and the cap sills 5 inches thick. Fig. 495. E The usual dimensions of cases are : shaft, 4 feet 6 inches by 3 feet 6 inches ; o-reat gallery, 7 feet 6 inches by 6 feet 6 inches ; branch gallery, 4 feet 6 by 3 feet ; small branch, 2 feet 6 inches by 3 foot 7 inches. SHAFT-SINKING IN SOFT SOIL. 2Git The stanchions for great fralleries liave no tenons at the lower end, but arc kept in tlieir position by blocks of ehn nailed to the ends of the gx-ound sills. (250). To sink a shaft in loose soil, an excavation of one foot is made and the first case is placed; the second and all the others are placed in the same way, but instead of excavating to the like depth of one foot on the whole ai-ca, the miner excavates first for one end only of each new frame, then for the other end, next for one side, and then for the other. Fio. 496. The shaft is completed thus to tlie level of the bottom of the intended gallery, and at starting, two sides of the cases ai'e placed exactly parallel to the proposed "direction of tlie gallery. To commence tliis, a fixed frame similar to a doorpost Fig. 497. is set up on the side of tlio shaft with its sill below the level of the intended floor, fitting exactly right and left : it i.s intended to support the lower casing of the shaft after the pieces are removed to excavate the gallery, its width and height being equal to, or an inch greater than those of the gallery. It is placed in its position after the miner has removed the lowest end piece, and the one immediately above Fig. 498. . 270 GREAT GALLERIES. it The other ends or side pieces are removed afterwards, until there is sufficient height for the gallery. The ground sill of each case is first laid, then the stancliions and the cap. The cap is fitted first with the tenon of one stanchion, and either the other end is raised up, or the head of the second stanchion is pushed out two inches beyond its proper jilace to adjust the tenon and mortise of that side, care being taken to cut away no more earth than is necessary. tz (251). Great galleries serve chiefly for a descent into the ditch, and may slope 1 foot in 4. They ai-e commenced by cutting a shaft 10 feet square at the bottom and 10 feet deep, and from the bottom a ramp is cut to the rear as a means of communication. This depth will leave 3 feet of earth over the cap of the gallery. The cases are placed perpendicularly to the slope. In making these galleries, after a case is set, a couple of crutches of the form of a T are used, the shanks of which rest on the last sill laid, whilst their heads, two feet long, project 1 foot beyond the last cap. The excavation being made wide enough to receive the next cap, this is laid on and supported by the projecting ends of the crutches ; the excavation is next continued Itelow to allow of the placing of the sill and the stanchions of the new case one after another. Tiie crutches being moved on to this new sill, the process begins afresh. The head of the crutch is braced to the shank by an iron l)olt to be made steady ; the foot is kept steady by driving a wedge into a groove cut in it, and the ])rojeetiiig end of the lioad is about an incii SMALL GALLERIES. 271 thicker, to enable each successive cap to stand at first a little higher than its final level. Notches 1 inch deep and 6 inches long, are cut on each side, about a foot from the top of these stanchions to allow of a man's hand passing through to adjust them. (252). Galleries once begun in loose soil should be carried on without inter- mission. When the soil is favourable partial casing only is necessary, and the cases are iuti-oduced at clear intervals of 3 or 4 feet, they are either notched into the earth, or the end pieces are supporti'd by pickets driven horizontally under tliem. . .....^ In making small ER. (256). The charge of powder is sometimes placed at the bottom of a shaft, sometimes at the extremity of a braiicli leading out of a gallery. In cither case, a cubical recess, called the chamber, is cut at right angles to the shaft or branch, so that its body may be out of the direct line of it. The powder is carried in I bags, containing 40 or ,50 pounds each, and is pom-cd into tlie clianiVicr, oi- into a scjuarc box made for the purpose, and placed in the chamber if the ground is damp. One pound of powder occupies 30 cubic inches. A powder hose, or a tube, 1 inch in diameter, of strong linen filled with powder is placed in it, and reaches the point where the miner is to ignite it ; generally it is protected by a wooden case, and fixed to the sides of the shaft by wooden pegs. More generally, Bickford's fuze is employed, wliich is a small waterproof flexible tube, containing powder covered all roimd with moist clay, and fired by a piece of portfire long enough to give the miner time to make his escape before the explosion : this method has the disadvantage of filling the galleries with smoke. The best method, when it is possible to employ it, is to fire the mine by means of a voltaic battery, or by Stratham's electric fuze. Previous to firing, it is necessary to tamp the mine, which is done by covering the chamber with a plank, closing the top with sods or sandbags, stopping the mouth in the same way, and placing struts between it and the opposite side of the gallery, filling the interval with .sandbags, &c. The tamping is carried on in the gallery sufficiently far to prevent the mine from damaging it. If it is at the bottom of a shaft, the whole of it is tamped. (257). When several mines are to be fired simultaneously, they are called conjunct mines, and the powder hoses or saucissons are brought together at the same point or fociis of ignition, their respective lengths to the chambers being equal to Fig. 514. Focus 0/ /yn 276 CHARGE OF POWDER. that of the furthest mine. The focus of explosion is the centre of the chamher itself. (258). The effect produced by a mine depends upon tlie quantity of powder used, the deptli at which it is placed, and the nature of the soil. If the charge is small, the explosion causes a mere splierical coni]iression ; but when the charge is sufficiently strong, the explosion raises the earth above, and forms a hollow circular opening or crater. An internal commotion is also produced, which may destroy shafts and galleries. The solid through which the commotion is felt is a kind of ellipsoid. The distances, AE, AD, to which this commotion extends are called radii of rupture : the radius, BC, of the opening is called the radius of the crater. The line AC dra\\ni from the charge to the edge of tlie crater is the radius of explosion, and the distance, AB, of the charge to tlie surface of the ground is the line of least resistance. One-lined, tivo-lined, three-lined, &e. craters are those whose diameters are e(ju:d to once, twice, three times, &c., the line of least resistance. Common mines are those forming two-lined craters. Under-charged mines and over-charged mines are those produced with a quantity of powder less or greater than is necessary to produce a two-lined crater. It has been found impossible to obtain craters of a radius greater than three times the line of least resistance, but the power of producing an interior effect of rupture has no limit. In a common mine, the major axis of the ellipsoid or horizontal radius of rupture is 1"7, and the minor axis or vertical radius is 1-3 of the line of least resistance. In a mine with the maximum crater, the horizontal axis is 4'36, the vertical 1 '4, showing that by increasing the charge the effects below the mine are slightly increased, whilst the lateral effects are much greater. (259). In order to find the quantity of powder necessary to produce craters of different diametei-s, express the line of least resistance in feet, cube it, and C A MOU KLETS— liL AST.S. 277 for a one-lined criiter multiply by -033, two-lined -I, three-lined -21, four-lined •45, Hvo-lincd 1, six-lined 1-75. The product gives the charge in j)ouiids. It corresi)ond.s to about 1 ! pounds for every cubic yai-d contained in the crater. The volume of the earth displaced in a common mine is generally considered as the fnistrum of a cone, having for its height the line of least resistance, for radius of its larger end the same line, and for radius of its smaller end half that line; the solid contents are therefore y I'- Allowing H pounds for a cubic yard, this formula may serve to calculate the charge ; the above method is more expeditious. Over-charged mines, or globes of compression, are sometimes employed by the besieger, and less frequently by the besieged ; they were recommended by Belidor towards the middle of last centuiy. The line of resistance I, and the radius of crater /•, being gi\-en in feet, the charge in pounds is ( ~ — — ) For under-charged mines the charge would be ( — iTT" ) The radii of rupture in this case arc the same as in common mines, but when the line of least resistance exceeds 10 feet, the horizontal radius of rupture z:z — , C being the charge in pounds. A sufficient number of experiments, however, have not been made to justify us in placing implicit reliance on these formulie. It has been found that in doubling the charge we can disjiense with the tamping, and that when the mine is excavated through different sorts of rocks, the charge found by the j)receding rules must be multiplied by a co-efficient: thus in — Light sand by 1*12, hard sand 1-25, wet sand 1-30, clay mixed with loam 1-55, fat earth 1"70, rock 2*25, good masonry or brickwork 2-2o, old and good ditto 2*50, new and inferior 1-60, best masonry 2-90. When exploding in open air, the resistance oflPered by the atmospheric pressure is nearly equal to the weight of a column of solid earth 12 feet thick. (260). A camoitflet is a small mine, charged with 10 or 12 pounds of powder, and formed in the wall of the enemy's gallery' to blow in the earth, (261). Blasts are small chambers or holes made in rock or masonry. The instruments required for making them are the jimiper, the scraper, and the hammer. A miner holds the jumper, turning it round, whilst another strikes its head with the hammer, the scraper serves to clear the hole. The charge occupies one-third of the hole, straw stalks filled with powder are dipped in it, and the blast is tiimped with pieces nf rock or sand. :,.J civ^^^ 278 CUUNTEKMINES. SECTION II.— COUNTEB-MINES. (262). Tlio defensive mines, or counter-mines, are generally constructed at the same time as the fortress, and as a great numher of systems have been proposed and employed without any one having such an advantage over the others as to be exclusively adopted, we shall confine ourselves to generalities and principles. Fig. 516 represents a disposition called the system of envelope galleries, fig. 517 tlic system of Gumpurtz and Lebrun, fig. 518 the system of Dufour; and many more exist, as those of Coulon, De Valliere, Belidor, Cormontaingne, Delorme, De Rugy, Mouze, Marescot, &c. The system of Dufour, however, is considered, in tlie main, to be the best. MACiLSTUAL GAI.LERIES. (263). A system of counter-mines generally consists of a gallery of counter- scarp, or magistral gallery, AAA, close behind the revetment of the counter- scarp, and of an envelope gallery B B B parallel to the former, and at a variable distance. The magistral and envelope galleries are connected by galleries of communication. From the envelope, listeners or listening galleries are pushed towards the country to meet the miner of the attack. Sometimes a gallery extends along the faces of the bastions and ravelins, especially where the breach is expected to be made, and is called an escarp gallery. (264). The magistral gallery has sometimes been constructed under the banquette, or under the middle of the terreplein of the covered way, especially when the system of counter-mines has been prepared after the erection of the fortress ; but it is prefcraljle to establish it immediately behind the counterscarp, since besides being more economical, it is better lighted and ventilated. It is 6 feet wide, and from 7 V to 9 feet high. As it follows the counterscarp, which is thicker under the traverses, it is not exactly in a straight line. It is pierced with loopholes, both for ventilation and for the defence of the ditch. Small magazines for tools, wood, powder, &c., are constructed close to the galleries of communica- tion. The entrances to the gallery from tlie ditch arc formed of doors which can l>o bolted inside the gallery, so that tiio niiiioVs may isolate themselves should the ENVELOPE GALLERIES. 1 '"" V w x'^^mtf^^'^t Vr\. fYW enemy succeed in reaching the ditch. The galleries of communication can also be isolated from the magistral, to prevent the enemy, who has entered the former, from occupying the latter, by means of sliding doors. These doors are loopholed. r\o and can be fastened by means of iron pins passing through the door into the wall. The great objection made against counterscarp galleries is, that the enemy having possessed himself of them becomes master of the ditch. (265). Envelope galleiies are now seldom used, because presenting their sides to the globes of compression of the enemy, they are easily destroyed, and when lost serve as a basis of operations to the besieger's miner. They are only employed for small portions. Their dimensions are 4 feet wide and 6 feet high. (266). The galleries of communication are of the same dimensions. They can be isolated from the envelope by sliding doors ; a recess may be made at the junction, which serves as a depot for tools ; the door is defended from loopholes, or it may be barricaded by filling the whole recess with sandbags. The galleries themselves can be closed by barricades of beams and sandbags; and grooves are prepared in both sides to enable the miners to slide the beams. (267). Listening galleries are 44^ feet high and 3 feet wide, and must not exceed 45 yards in length, because the air becomes unfit for respiration beyond that distance. These galleries are made to enable the miners of the defence to JSTENING GAUT.ERIF.S. 2?<1 catch the sound of the blows of the enemy's tools, which he can hear if they are l)roduced within a distance of tiO feet ; and sliould lie thus obtain a warning of his approach, he commences a small branch to take liiin in flank. The listeners should not be more than 120 feet apart, so that the enemy cannot pass between them without being heard, and they should not be nearer than 48 feet, because with the usual line of I'esistanco of 15 feet (270) two mines. exploded in parallel listeners less distant, would overthrow the whole ground between them. At the distance of 48 feet, the effects of the radii of ru])turc will defend the interval very well. In order to save time, openings are left at intervals of about 30 feet on the walls of the listeners, to facilitate the execution of the small branches ; they are closed by thin walls, to prevent the earth from falling : grooves are also made at intervals of 8 or 10 feet, to facilitate the tamping by inserting beams, &c. (268). Chambei's of mine may be placed anywhere in the galleries themselves, or in tlie branches leading from them ; but it is necessary that the position of those nearest to the covered way, intended to blow up the breaching and counter batteries, should be well detennined, because their explosion might blow up the crest of the glacis, and expose the defenders. These chambers should be all placed in a plane inclined at 45° to the horizon, and passing at a distance of 24 feet from the crest of the glacis; and the small branches leading to them may be prepared beforehand. At the point of juncture of two or more galleries, small vaulted ciianibers are usually constructed to facilitate the movements of the miners, and to serve as a tlepot: they are circular, rectangular, &c., and covered with a dome or with 282 ESCARP GALLERIES. groined arches. An aperture in the arch in communication with the soil serves for ventilation. Similai- chambers are also made in the middle of long galleries. (269). The escarp gallery, when constructed, is 15 or 20 yards in rear of the escarp, and communicates with the interior retrenchment by a gallery in the capital, and two galleries parallel to the flanks. It serves as a base of a system of branches leading to mines prepared under the places where the breach and the enemy's lodgment are usually made. As the chamber a is about 3 feet below the ditch, and chamber h at half tho height of the revetment, the escarp gallery must bo 2 3'ai-ds above the bottom of the ditch, or at such a level as will not require too great a rise or descent to reach either mine, the maximum slope of a branch being 1 in 4. The escarji gallery may be connected with the magistral. It is true that, as the counterscarp gallery runs romid the whole place, the miner may enter it at distant pomts to repair to the front of the attack by a circuitous way, but as it is prudent to barricade that gallery, to prevent a surprise, the miners would be obliged to cross the ditch, which is somewhat dangerous towards the latter part of the siege. A gallery of communication from the escarp gallery obviates this necessity, but it is liable to be filled with water, and its entrance by means of steps or ladders is inconvenient. (270). The depth at which counter-mines should be constructed is now admitted to be from 4 to 6 yards. Before the discovery of tho globes of com- liression it was recommended to have several stages of galleries, one above the DEPTH OF COUNTERMINES. other, so as to blow up the ground several times in suecession; but General Dufour has clearly j)ro\ed that the chambers of defensive mines should be in the same plane, at a depth of from 4 to 6 ;/ai-ds beloio the surface. Wo give here his denionstration, translated in tlie " Aidc-Mcmoirc." Let nov^ MN represent the water level, and B, B' two mines placed as low as practicable, as regards the water level, which mines are supposed to be 30 feet below the surface of the ground ; let C C C" C" be the position of defensive mines, placed at half the depth of the first mines B, B', and, like them, separated from each other by intervals equal to twice the line of their least rcsistivnee. The besieger, in tlriving his gallery as low as possible, would place his mines as near as he deemed prudent to the defensive mines B and C, and load them as globes of compression, or surcharged mines. The solids of rupture of the defensive mines B and C are represented by dotted ellipses. It will bo observed that they keep off the besieger's third parallel, equally distant from the covered way, when the most advanced mine (C) of the upper system is carried forwards a few yards in front of the most advanced line of the lower system (B). The besieger's miner, then, endeavouring to give to liis offensive mine (A) tlie greatest possible destractive action, woidd load it with GOOO or 70001b. of powder, which would give to his horizontal radius of rupture a value equal to four times the line of least resistance, while the vertical radius of rupture would somewhat exceed that line. But as in ordinary or common mines, the semi-axes major of the ellipsoid of rupture may be practically taken at about 1 ^ times the line of least resistance, it follows front the figure that from B to O the distance is about .'3;, times tiie line 284 DEPTH OF COUNTERanNES. of least resistance ; and that, consequently, the second mine B', as well as the first mine B, would be destroyed by the same explosion. With regard to the upper system of mines, there will bo three of them within the cii'cle of destruction of the mine A ; the fourth C'"- being exterior to the ellipsoid of rupture, might be shaken but not destroyed. Therefore, by the explosion of the besieger's globe A, supposing all tlie defensive mines in the figiu-e to be charged, the two lower ones, B B', containing each 27001b. of powder, will occasion a loss of 5400 lb. to the besieged ; while the four mines, C, C C", C", containing only 337 lb,, would entail a loss of 1001 lb. If, also, the extra tamping be taken into account, as well as the framing for the galleries, which is necessarily more considerable in two large than in three small ones, it will be found that the same explosion of the besieger will cause to the besieged a loss at least five times greater than what he would have suffered if his chambers had been placed at cue half the same depth. Thus, therefore, under the inevitable losses which the besieged must necessarily experience, the defensive disposition C, C, C", C", appeal's to have obvious advantages over that oiJered by B, B'. On the other hand, the mine C, from its downward or subvertical action, will prevent the besieger from passing below it, and equally prevent him from advancing beyond the line b h> as the mine B does. Both mines B and C would reach the enemy if he passed the line b b' , with this difference, however, that the mine C would eaiploy, so to say, all its force, at an expense of 337lb. of powder to the besieged; while the other mine (Bj expending a part of its effort in destroying the tenacity of the ground below, would cause an expenditure of eight times as much powder as mine C. It is from not having considered the effects of mines, in a subvertical or downwai'd direction, that authors on this subject have fallen into the error now controverted, ^^z., " That the besieged ought always to occupy the lower position for his mines." The superior disposition will require, it is admitted, galleries pushed more in advance, and will cost, conse- quently, more, all other conditions remaining the same ; but can an expense incurred at the time of the construction of the defensive mines be compared with that which results from a considerable consumption of powder, at a period of the siege when it is generally found to be deficient, and when no means can be resorted to for renewing the supply ? And, besides, this prolongation of the galleries is not lost to the besieged, since the enemy, who generally is aware of the depth at which the mines are situated, would establish his third parallel at a distance from the rest of the glacis proportionably greater. If to these advantages, which a system of mines situated at a moderate depth possesses, are added those of a readier mode of tamping, of greater salubrity, by gotthig rid of the water, and of economy in their first construction,— an economy due to the galleries being nearer the snrijice, which allows them td be constructed colT^■TER^[I^■Es, 285 in cuttings, instead of by tiie laborious process of tunni'liiniT) — it will, it is conceived, be conceded that no tloubt can exist of the advantages of the two systems, C, C, C", C", and B, B'. The upper system will therefore be selected, as situated at the most appropriate depth for the subterranean defence ; and the principle will be assumed, that the chambers of defensive mines should be in the same plane, at a depth of from 12 to 18 feet below the surface. The position of the galleries which conduct to them, should be in another plane passing through the bottom of tlie ditch, at the foot of tlie counterscarp, and rising ai such ail inchnaiuni as lo interseci ilic plane of the mines under the foot of the glacis. The plane of the galleries will therefore be favourably disposed for di-aining off tlie water and keeping them diy. Tlie mines, disi)osed as above explained, may be placed in the gallery when the latter is coincident with the planes of the mines ; but generally the mines are reached by branches driven from the main galleries. (271). When the besieger has constructed his third parallel, he commences his mining operations to discover the galleries of the besieged in order to blow them up, and to make safe of the gi-ound below, before advancing further on the surface. The miner of the defence proceeds from his listening galleries to meet him. Both miners listen attentively for the sound of the pickaxe, so as to judge in which direction they must advance. Sometimes one of them, hearing his enemy approach, will stop working, to avoid giving him warning of his presence. When they ai-rivc within four or five yards of each other, they employ camouflets ; and when their branches meet, the miner who first perceived it pierces the earth with a borer, and fires a rocket through the hole to poison the air. As soon as the miner sees a borer, he must, at the moment it is withdrawn, fire a phtol through the hole, and endeavour to give his cainoiiflet first. If they meet they fight with arms, and try to seize each others galleries, and to find the chamber of mines, either with a view to take the powder, or to saturate it with water, or else to cut the wire that connects it with the battery. In his subterranean warfare the besieged fires common mines, only because he must economise his powder; and he avoids forming wide craters which tlie besieger can occupy. 286 GLOBES OF COMPRESSION. (272). The besieger, on the contrary, will employ globes of compression. A first globe, at a depth of 7 or 8 yards, loaded with 4000 pounds of powder, will destroy the extremities of the galleries. The crater is at once occupied with the flying sap, and from it advance is made further into the system of counter-mines, when a second globe is fired, then a tliird, and a fotirth will generally blow in the counterscarp. The defenders will oppose his advance, fire a few mines, delay him, kc. It is calculated that a system of counter-mines will arrest the besieger dm'ing forty days at least. An engineer * lately observed that " countermines are as indispensaljle for a front attack as parapets and flanking fire, and that Vauban had, tow:u-ds the latter part of his life, very properly advised Louis XIV., then in adversity, to construct them in all his fortresses." Bousmard also said : " Forty-two miners, properly employed, can double the duration of the resistance of a forti'ess, and counter- mines, whether constructed before hand or not, are the most powerful means of defence ; the very means which, in. ease of a choice, must be preferred to all others, and for whose entire development everything must give way. They deserve the preference were it only on account of the support they give to other means of defence : artillery and musketi-y act most powerfully when the mines have uncovered the besieger ; works of defence and fortifications are never so much di-caded by the besieger as when he knows they are comitermined." Unfortunately the advice of Bousmard has not more prevailed than that of Vauban, and in France, from 1810 to 1840, not one gallery, nay, not a branch was constructed. (273). We may here mention a method of attack by mining proposed by Gillot, a French engineer. After the construction of the third parallel, the approaches are suddenly stopped, and at night a flying sap is made between the parallel, and the crest of the glacis. In this trench the miners sink shafts 6 yards apart, to the depth of about 9 feet. This can be done in less than five hours, during which the besieged cannot alter his dispositions : 300 or 400lbs. of powder are placed at the bottom of these shafts, and all these mines lieing fired simultaneously, the counterscarp is insulated from the branches and their chambers. A similar operation executed the following night in the covered way completely destroys the magistral galleries. Experience has not yet proved the value of this method : it can only be attempted when the garrison is demoralized by former attacks. It may cause to the besieger as severe a loss as the storming of the covered way ; and in case of failure, the siege must be raised, or the attacks be i-esumed with the usual regulai-ity. (274). In order to open a breach by the mine, the charge should l)e placeil • Prevost do Veruois, l)e la Kortilication depuis Vauhan, ISCl. Ol'KNIXG A nREACII BY A MINE. 2H1 behind tlio escnr]i, in rear of the counterforts, from 2 to 3 tcet above the ditcli (.528), or 1 foot above the level of the water (529), and at a distance In Fig. 529. Fig. 530. tlie terreplein, not less tlian twice the line of resistance, or the length from tlie charge to tlie face of the wall. Vauljan placed the mines at a distance from the face of the escarp equal to ,} or } its height, near the tails of the counterforts. rZ: 'JT lie computed the ehai-go at ^ more than for a mine in common earth. If, instead of milking a breach, it is merely wanted to destroy the escarp, the charge is placed near the base of the wall, in the middle of each counterfort, in a lin(! with the back of the wall, and is equal to 4- the cube of the thickness, the chambers being disposed at two-lined intervals. If the wall has no counterfort the charge may be placed at the back of the wall at two lined intervals, in which case it is -/,; the cube of the thickness. To destroy a wall standing alone, a barrel of powder is placed along it at its foot. If the thickness varies from 5 to 6 feet, the chamber must be placed under the foundations, and if the thickness averages from 9 to 12 feet, a branch is driven 288 DESTRUCTION OF POWDER MAGAZINES. at the level of the ditch ; and the charge, computed at ^ the cube of half the thickness, is placed in the centre of the wall at two lined intervals. To destroy a wall by blasting, tiie hole is bored at 45° downwards ; to the centre of the wall, and as much beyond it as will hold half the chai-ge ; the charge z^ V ^ ' > I being half the thickness The holes are at two-lined intervals, their diameters vary from ji,^ to -fV the tliickness of the wall ; frequently two holes instead of one, exactly opposite to each other, are bored from contrary sides of the wall, and unite in the centre in the form of a V or an X. To destroy galleries of countermines, barrels of powder ai-e placed along them ten feet apart, the total depth not exceeding 15 feet, and both ends are blocked up. To destroy powder magazines or bomb-proof buildings, the charge is {)laced on the floor, at intervals equal to the line of least resistance ; tliis is equal to the distance between the floor and the external surface of the building: the charge rrJ^ l\ The door should be shut, and the windows blocked up with timbers. In a casemate, the charge should be nearer to the front than to the open end. To destroy a barrier gate, the charge of powder, from 50 to 100 pounds, according to solidity, is attached, with a gimblet or spike, and fired with Bickford's fuze. To destroy bridges, the piers are mined as for walls, but when there is no time, a trench is cut over the key of the arch, 18 inches deep; and 400 lbs. of powder are placed in it, and covered with timber and earth. It has been fomid that in regular mining and blasting the charges must be increased by y, or even ^, to obtain a violent instead of a moderate demolition. 289 CHAPTER XVIL SYSTEMS OF VAUBAN. VAUBAN, FIBST SYSTEM. (See 185.) (27.5). Tlie line of front, fixed at 360 yards, is a mean between the extreme limits which ean he given to permanent fronts, with the ix'licf adopted by Vauban. The minimnm 300 is determined by the condition that the entrance of the postern on the middle of the curtain should be seen and defended by the musketry of the flank. The maximum 400 is obtained by the condition that the lines of defence should not exceed the effective range of musketry, (see 94.) Thus 360 is the length of the ordinary or moan front. The condition of seeing the posteni T — -A- from the flanks is the basis of the alterations made to the relief when the length of the front is imposed upon us. Thus, if the front were only 240 yards and the relief 44 feet, there would be a dead angle before the curtain, and it would be so for every relief above 36 feet. [j - r 1 (276). The perpendicular vAries from Jth to Jth. The flanks are destined to defend the breach, and are counter-battered by the batteries established at the crowning of the covered way of the bastions : the besieger has a space equal to 40 yards — 30, tlie width of the ditch, added to the 290 SYSTEMS OF VAUBAN. 10 of the covered way. To have any chance of resisting these counter-batteries, the flanks shoukl therefore not be less than 40 yards. In the hexagon, the per- pendicular ^th gives tlius 54 yards. If it were made longer, the preponderance of tlie flanks would increase, but the angle of the bastion would liecome too acute. This latter consideration renders it necessary to sliorten it for the square and the pentagon, the angle of these polygons being smaller. All bastions arc thus maintained of a proper size, but the flanks are shortened, and this is a drawback which is obviated by making the ditch somewhat narrower. (277). The faces of the bastions ai'e made equal to 4-ths of the front. Vauban in adopting this dimension, had in view the necessity of giving to the flanks a proper length, but the bastions are rather small, and cannot easily be defended in rear of the breach. (278). The construction of the flanks by means of the circle described from the opposite salient as centre, gives to the angle of defence only 85° in order to defend at the same time the curtain and the face of the bastion. (279). For ditches destined to contain water, Vauban increased the width from 30 to 36 yards. These wet ditches have tlie advantage of altogether pre- venting surprises, and of allowing a reduction in the amount of the garrison. The besieger has no longer an easy access to the breaches ; a dam must be constructed, thereby limiting the front of the columns of assault. Two breaches only can be assaulted at one time, and the enemy cannot employ the ditch as a depot. On the other side, the communications between the enceinte and outworks are difficult : they are established at the moment of need by means of bridges, which consume both time and labour, and after all constitute but a precarious communica- tion, since the besieger wiU not fail to enfilade the ditches. As soon as the crowning of the covered way begins, the garrison can only communicate with the outworks by means of boats concealed in a little harbour reserved at the gorge of the ravelin. The defence is thus rendered less vigorous. In winter the water may freeze, and then M'ide cunettes must constantly be cut tlu-ough the ice. Dry ditches possess properties of an opposite chai-acter, the communications being safe and almost indestructible; sorties can be made, and the defence assume all its power. Wet ditches will therefore be preferi-ed for small places, dry ones for fortresses well scarped and well garrisoned. The best jilan is to have ditches that can be filled and cmjitied at j)loasure: in this case, they are kept full as long as tlie besieger cannot attack the outworks; FIRST SYSTEM. 291 but when sorties become necessary, and when the possession of the outworks is to be disputed inch by inch, the water nuist disappear. The descent into tlio ditch is then easily submerged; the passage, too, is hindered by chasses, &c. If, however, :i depth of water of 6 feet cannot be obtained, it is better to renounce the use of it, inasmuch as it then becomes an impediment to tlio defenders, without being an obstacle to the besiegers. (280). The counterscarp of the main ditch is directed towards the shoulder- FiG. 537. angles of the bastions, to give full scope to the flanks; if it were to lie kept parallel, a part of the defence of the flanks would be lost. (281). The tenaille is traced on the lines of defence, and has a small relief, so as not to mask the artillery of the flanks. It can thus give a grazing fire on the terreplein of the ravelm, to prevent the besieger from occupying it, and also an oblique fire on the main ditch. It covers the revetment of the curtain and of the flanks, and gives in its rear a good space for the defenders to collect in safety. The passage of 8 yards at its exti-emities, called trou de tenaille, has the defect of enabling the besieger to breach the flank from the crest of the re-entering place of arms. However small its relief may be, this work will always contrary to some extent the action of the flanks in the ditch, and give dead angles along these flanks. The Caponier is merelj' intended to cover the defenders in passing across the ditch from one work to another. (282). The ravelins constructed before Vauban's time, were very small ; their object was to cover the gates of the place and to protect the covered way, yet the besiegers were obliged to caiTy them, either before or at the same time with the assault on the bastions, because the breach of the latter would have otherwise been exposed to reverse fire. Vauban increased the saliency and made of the ravelins a very important work, the long faces of which carry artillery, and render the advance on the capital of the bastion very diflicult; when the polygon has many siiles, the saliency of the ravelin is such that the enemy must take it before attemjiting an attack on the bastions. The interior of the ravelin of Vauban is sufficiently large to enable the defenders to construct some interior intrenchment therein. The faces are directed to a point 10 yards fi-om the shoulder angles of the bastions, to protect the flanks from the enemy's establishment on the crest of the glacis. r 2 292 SYSTEMS OF VAUBAN. It must however be observed, that the escarp only of the shoulder angle is covered, and that the flanks are not : their command over tlie ravelin exposing them to reverse and enfilade. The ravelin has also the disadvantage of masking the fire of the curtain, and of being much exjxjsed to enfilade. The ditch has the same depth as the main one, and it leaves an opening called the " trou " of the ravelin, wliich enables the besieger to breach the face of the bastion with the counter batteries of the salient of the covered way, a serious inconvenience, which modern engineers have attempted to obviate. (283). The covered toay is, as its name implies, a path which was originally destined to receive small posts, to enable sentries to go their rounds and observe the enemy, to afford a cover to the men preparing for sorties, and also to them when afterwards retreating, so that tlie gates of the place might not be exposed. A banquette was subsequently erected, and the covered way became a defensive work, giving a strong grazing fire on the approaches. Vauban gave it a com- mand of 8 feet and sometimes less, but its glacis does not mask sufficiently the masonry of the escarp, a great defect, which his successors corrected. He made it 10 yards broad only, to pre\ent the besieger from establishing his batteries in the terreplein, a width sufficient for the occupation and the free circulation of troops. The glacis has a gentle slope and cannot be destroyed, as \\ould a mere parapet; the besieger must advance on a surface well defended, and has to excavate his crowning to obtain cover for his batteries, a labour of no small diflSculty. The re-entering places of arms are destined both to permit the garrison to form before making a sortie, and to flank the long branches of the glacis ; for this latter reason Vauban made their angles of defence 100°. They form excellent posts, which permit the defence of the counterscarp to tlie last moment. The sally ports are directed towards tlio crest of the salients of the covered way of the ravelin and bastion, to prevent the enemy fi"om enfilading them. They are 4 yai'ds wide, a width more than sufficient, because 5 men can march abreast through them ; and at 80 paces per minute 400 men can file off' through one port. The object of the palisading is to increase the security of the defenders, and to jirevent the enemy from jumping into the covered way ; but it is far from aelding strength to the defence, because the palisades arc in the way of the muskets. Besides, the men cannot be close to the crest, and are more exposed. In 1697, at the siege of Ath (some authors say in 1688, at the siege of Philips- burg), "Vauban used the ricochet fire for the first time ; and he afterwards threw up traverses along tlie covered way, about 30 yards apart, the distance of the flight of a ricocheting ball. Those established at the salient places of arms are iilacc'd .Ml til.' rear .>f the fa.-es <^F the ravelin ■•uid .jf the ImsChis. so as not t.> SECOND SYSTEM. -2118 aftbrd shelter to the enemy, and also to expose their terreplein to the view of the enceinte. These travei-ses intercept most of the flank fire directed from the enceinte on the covered way, and prevent a rapid circulation, and since they oblige the defenders to pass through narrow crochets situated exactly under the crest of the glacis where the enemy comes, they render their retreat difficult. Vauban has therefore recommended a little trench to be dug during the siege, along the top of counterscarp on the rear of the traverses, into whicli the defenders can retire to avoid being seen by the enemy. SECOND SYSTEM. (284). The rapid progi'ess of the art of attacking fortresses, and especially the tliscovery of ricochet fire, induced Vaul)an to modify his tracing. As the loss of the bastion was al\va\-s followed by that of the town, he transformed the bastion into coiuitcriiuurds or outworks of the form of a lunette or a redan. o o' being the side of the polygon to be fortified zz 280 yards, he erected at the angles bastioned towers A, B, in masonry, to flank the ditch of the enceinte. These towers contained two Casemates,* or ' subterranean vaults built bomb-proof; the first 6 feet above the level of the ditch: each casemate had two guns firing through embrasures on each flank, making altogether eight guns only for the ditch. • Casemates, from the Spanish, ' casas-matas,' slaughter-houses; thus named bcciuse when these subterranean vaults were first employed it was supposed they would occasion great slaughter. The smoke generally disqualifies them from serving the artillery with any clTcct, but they constitute good shelter for men and ammunition during a siege. 294 SYSTEMS OF VAUBAN. THIEl) SYSTEM. (285). In his third system, the front A B Ijeing, as in tlie first, 360 yards, he gave an additional defence to the ditch by tracing a bastioned cm-tain witli a perpendicular equal to 10 yards. In tliis system the scaqis were built of masonry to the level of the ground only, thereby giving a great exterior slope to the parapet. A berm of 10 feet was reserved at the top of this scarp. TRACING THE SECOND SYSTEM. (286). Let 0' (Fig. 538) be the side of the polygon to be fortified, oo' — 280 yards. At each angle is a tower of masonry : its demi-gorgo measm-ed on the bide of the polygon is 10 yards long ; its flanks are perpendicular to the curtain and measure 16 yards, m nzz. 12, and « j) ^ 4 ; its salient angle z= 90°. The salients s, s' of the bastions transformed into counterguards are at the dis- tance of f ths of the front o o' from the salient angles of the towers ; the faces are directed on the flanking angles n n' of the enceinte : the shoulder angles are determined by circles described from the salients s, «', as centres and radii S g', S' g, the points g and g' bisecting the semi-curtains Co, Co'; the flanks are directed to a, a' taken at 2 yards from g, g'. The extremities of those flanks are obtained by joining mh' and m' 7i ; the intersection of /i ?>i' and ka limits the flank of the left counterguard, that of h' m and k' a' the flank of the right. This con- struction prevents the besieger, when arrived in one counterguard fi-om getting a view of the other, and gives the flank of a tower a sight of the salient of the next. The demi-gorges of the counterguards coincide with the lines mh', m h, as far as 20 yards from the flanks, and become tangent to circles of 14 yards radii, described from the salients of tlie towers as centres. TKACING TIIK SECOND SYSTKM. 29') The tcnaille is traced on the Hues of dcfbiiee ; its rear is on tlio lino that joins tlie extremities of tho flanks, and its profiles arc parallel and at 10 yards from these flanks. Tho ditc-h in front of the connterguards is traced as in the first system, 30 yards wide at the salient, and its counterscarp is directed on k, k'. The capital of ravelin is 90 yanls, the faces are directed to 20 yards, fi'om the shoulder angles h, k', and they have flanks determined by taking off 20 yards on the faces and 14 on the demi-gorges. The rest of tlie front is traced as in the flrst system. Tho commands of this system above the gronnd are for towers 24 feet, counter- guai-dsand enceinte 22 feet, ravelin 18 feet, glacis 8 feet, ditch 20 feet deep. TKACING THE TIIIKD SYSTEM. (287). To trace the third system, Vauljan took the line of front A B (Fig. 539) oqnal to 360 yards, and constructed a front of his first system on it, with these dif- ference-;, tliat the faces of the bastion were a third of the front, that tlic capital of the ra\e]in had 110 yards, and its faces were directed at 20 yards from tlie shoulder 296 SYSTEMS OF VAUBAN. angle, and that the capital of its redoubt was 45 yards. The flanks of the ravelin were traced as in the second system, and those of the redoubt were parallel to them, and equal to fths of their leugtli. The ditch of reduit was 10 yards wide. The old curtain being produced, till it cuts the radii of the polygon, the inter- sections determine the salients of the towers: pai-allel to it, and 18 yards in rear is the interior side, on which a bastioned front is constnicted with a perpendicidai- of 10 yards, and with flanks traced on the prolongation of the flanks of the counterguards. To trace the towers 14 yards o a are taken on the interior side, and at that point a perpendicular is drawn 12 yards from a to h, and 8 yards from a to c. The face is formed by joining D h. The ditch of the tower is 14 yai-ds wide at the salient, and the demi-gorge of the counterguard after following the old curtain for 20 yards, becomes tangent to the circle of 14 yards. The tenaille traced as on the first system on the lines of defence has its gorge on the old curtain, and its profiles are parallel to and 10 yards fi-om the flanks. The commands were : — towers 22 feet, counterguards and enceinte 20 feet, reduit in ravelin 17 feet, ravelin 14 feet, glacis 8 feet, ditch 15 feet deep. TRACING THE THIRD SYSTEM. 21t7 In these two systems, the bastioned towers contain casemates sej)arated by a strong i)illar of masonry. Access is given to these casemates by posterns that cover the staircases to the platforms at the gorges of the towers ; tiie same pos- terns also lead to the ditch and to small bridges that serve as communications between the enceinte and the counterguards. Similar bridges lead from the counterguards to the tenailles, and the tenaillcs are also reached from the ditch by means of ramps. The top or platform of the towers, consists of a mass of cai-th rammed down over the casemates : it is provided with a parapet of bricks 2 yards thick, with two embrasures on each flank, and banquettes along the faces. In the towers of the third system, this pai'apet is also constructed along the gorge, in order to con- vert the platform into a reduit ; and a splinter-proof traverse is placed at the centre. The small flanks of the third system, contain a casemate for two guns each, at the same level as those of the towers ; they are entered by posterns established in the cui-tain. In the thii"d system the revetments of the ravelins and counterguards are not carried up higher than the level of the ground, very likel}' for the sake of economy. The exterior slojies have thus a great size, and a berin of 10 feet runs along these works between the top of the revetment and the foot of the exterior slope. Section aud Profiles of the Third System. SYSTEMS OF VAUBAN. The revetments of the enceinte and of the reduit of ravelin are raised up to the level of the exterior crest of the parapet ; the thickness and slojie are the same as for the first system. They are called full revetments, to distinguish them from those of the ravelins and counterguards, which are called demi-revetments. In full revetments, the part of the wall above the level of the rampart is only 3 feet thick, and has no slope. In these systems as well as in the first, Vaiiban has constructed some stone sentry-boxes or tm-rets called guerites, at the top of the revetment of the salient igles. They project over the ditch, sn that sentries jjlaced in them command PltOPERTIKS OF THESE SYSTEMS. 2^ the ditch through looplioles without being exposed to musketry fire. It was formerly the fasliion to ornament them ; but this lias been abandoned because it marked the position of the salients, and facilitated the taking up of the prolonga- tion of the faces. PROPERTIES OF THESE SYSTEMS. (288). The advantage of these systems are, that the enceinte of the place cannot be breached by the batteries established before the salient of the i-avelin, and the enemy has first to occupy the counterguards ; and as these are com- manded within a short range by the enceinte, he will find it most difficult to construct breaching batteries in tlieni. The towers protect the enceinte against enfilade, and afford great security to the guns in the casemates against vertical and direct fire. The defects are, that the towers being made of masonry, their platforms are much exposed to the effects of splinters, more so in the second than in the third system. In this system the towers can serve as reduits, and they will flank the terreplein of the enceinte. The flanks of one tower cannot efficiently defend the faces of the other two, owing to the gi'eat projection of the counter- scarps of their ditches. But, what is worse still, the towers can be so injured before the counterguards are taken as to become useless in preventing the besieger from erecting batteries against the body of the jilace. The flanks of the comiter- guards are too small for the defence of the main ditch ; the ditch of the enceinte is only flanked by eight gims in the second system ; in the third there are sixteen guns, but the small flanks being in the prolongation of those of the counterguards are exposed to enfilade. The ravelins with flanks have the inconvenience of exposing the shoulder angles of the counterguards, and of enabling the besieger to breach the enceinte from the lodgment of the re-entering place of arms through tlie openings of the tenaille ; this defect is somewhat less in the third system, where the greater saliency of the ravelin will besides prevent the enemy from forming a lodgment at the salient of the covered way of the bastion, before he has can-ied that ravelin ; it will also oblige the besieger to open his trenches at a greater distance: the reduit will prevent him fi'om forming lodgments in the ravelin. In weighing the advantages and defects, it is veiy doubtful whether the defence gains anything ; and as the expenditure in masonrj' is doubled, these systems have not been employed since Vauban's time. THEIR ATTACK. (289). The methods of attack for the second and third systems are the same. For polygons of fewer than eiglit sides, the process is the same as for the first system, until the counterguards are taken (.203): for higher polygons the saliency 300 SYSTEMS OF VAUBAX. g 3 Oe. pCR >2. r- §__«. ^3 go g>^o |. 8 ~ ?i &" 4^ C o B 3 Cf K o g S II I'll! 1^1 ' ^ I s ? r i- 1 ^ S- i I. o a: |. I- - ^ 5 o 2 p g: §- i ' ? n> o -• w o B " I- 1 : i 2 t K4 s- -1 §" §" I g — C ft-c^K- costs 5 a o -„ g- - ^ 2 3 '^ „ O < 3 O ■ 3^ 53 (T*- ^ 3 § ^ !§■ ^' I ^ - i p a 3 ^^ ro\^ ^3" - "^ ^ s, 3' e c- s ' ¥ < ^ i ^^''^ ^"^ gS.2 3 £ S-cro o 3 3"S'2§"'n'5^ -^ B- ^ i ^ i- ^ i s _-&''=n>3p_£.:^ o>-s o o C:.3-roo ? r 3- S § 3 ^ s a o f^ <^ 2. g g E? CR en; »t "■ n ^ S S S. ►« 5 3 S ro < I g r^€g.^ OUILLON. 301 The reduits of ravelins are taken on the twenty-third niglit The lodgments are first enlarged to receive a few mortars (5, 5) for firing stones at the garrison ; then breaching batteries (6, 6) are constructed in front ; and a descent gives access to the ditch if the besieger does not blow in the counterscarp. The same night, the glacis of the re-entering places of arms, and the covered way of the countcrguard, are completely organized, the former into a battery (7, 7) to breach the body of the place through the opening of the tenaille, the latter into counter- batteries (8, 8) against the flanks of the collateral countorguards, the passage along the ditch of the ravelin advancing as far as the main ditch. On the twenty- fourth day, under the protection of the counter-batteries (8), the passage of the ditch reaches the breacli of the countcrguard, and the assault is given. The lodg- ment is made, and from its extremities the besieger runs a sap through the parapet in order to drive ofi" by musketry fire the defenders of the tenaille, whilst another sap is pushed on between the tenaille and the flank of the countcrguard. The following night, the breaching batteries (9, 9) are completed in the reduits, which together with the batteries of the ravelin and of the places of arms, enlai-ge the breaches of the enceinte ; at the same time, the besieger erects in the counter- guards some batteries (10, 10) to countei--batter the enceinte, and more especially the cascmated flanks having view on the breaches and the tower, and sinks shafts in the lodgment, to run galleries to the counterscarp, opposite the shoulder angles of the tower. These galleries will pei-mit the lodgment of chambers of mine, which, by their explosions, will throw a sufficient quantity of rubbish to mask the embrasures of the casemates. The batteries are ready on the tweuty-ninth, and the mines on the thirty-first only ; in the meanwhile, the passage of the ditch has entered the ditch of the enceinte in full sap, and reached the foot of the breach. On the thirty-second night, the mines are sprung, and the assault is given at daybreak. FIIiST SYSTEM OF VAFBAN. (290). To complete all that relates to Vauban's systems, we may allude to the first of his tracings, which differs from the fi'ont which we have given before. It is only step by step that Vauban improved this tracing ; and the front called his first system, contains all the improvements which he successively carried out. The enceinte was first drawn as explained ; and in order to conceal some artillery, and keep it intact on the flank for the defence of the breach, he gave an orillon to the flank. An orillon may' be defined to be a prolongation of the face of a bastion beyond the flank. It was used by the engineers of his time, who found it advantageous to pi-otect the several flanks of their bastions, but the expense of tlic masonry which it necessitates is out of proportion to the advantages gained SYSTEMS OF VAUBAN. Fio. 550. when no such flanks exist : the gun to be concealed may be struck at reverse by ricochet, or a shell may destroy it. To trace this orillon, Vauban takes the thii'd part a c^ of the flank for gorge : tlu'ough the middle I, he erects a perpendicular 1 0, and from the extremity a of the face a perpendicular a o, to it ; the inter- section of these perpendiculars gives the radius a o, which serves to describe the orillon from centre o. From the salient A of the collateral bastion, the lines Ac, Ab are drawn to the interior extremity of the orillon, and of the original flank ; on these lines produced, c h and b d are taken equal to 10 yards, the curtain having thus a hrisure bd, and the wall c A, forming the reverse oi the orillon. Instead of tracing the retired flank along h d, lie described an equilateral triangle on that line, and from the vertex m as centre, and radius m h, he traced the curved flank. The first tenaille of Vauban was also diff'erent from the tracing he adopted afterwards : it had faces, flanks, and curtain. The faces terminated at 8 yards from the orillons, their length, st, being equal to half the line of defence, s p. The flanks were pai'allel to the original straight flanks of the enceinte. The curtain was traced parallel to, and at 22 j^ards from the curtains of the enceinte. The thickness of the faces and flanks was 15 yards, but that of the curtain was only 12 yards, in order to leave 10 yards passage between its gorge and the enceinte. This tracing was soon set aside, because it exposed the defenders to reverse and slanting fire from the salient of the covered way of the bastion, thereby rendering the tenaille useless for the defence of the ditch. The demi-lune was traced by describing a circle with the flanking angle b, as centre, and radius b g : the intersection r, of that circle with the perpendicular fixed the position of the salient, and the faces were directed to the extremities a, g, of the faces. It had flanks traced like those of the second and tlm-d systems. Tlicso flanks were destined to receive four guns each to fii-e on the breach of the bastion; but we liave seen that tlie salieiicv i>f tills ravelin was imt sufficient to FIHST SYSTEM. 303 prevent the besieger from attacking the bastion before tlie raveh'n, and that the Hanks had the defect of exposing tlie shoulder angle of the bastion antl their flanks to be breached fi'om the counter-batteries of the salient of the covered way. The figs. 551, 552 represent tlie profiles of this first system. The duration of the siege of a place of this sort has been estimated at nine- teen days. Fig. 553. 304 CHAPTER XVIII. MODERN SYSTEM. (291). Cormontaingne, a disciple of Vauban (471), is the author of a system which was first applied in 1728 and 1735 to the forts Moselle and Belleeroix, at Metz. After having received some modifications from modem engineers, it has hecome known in this country under the name of Modern Front. Supposing the line of front =z 360 yards, the perjiendieulars are fixed, as in Vauban, at ^th, i th, Jth. The faces of the bastion are V«l of the front, 120 yards; the flanks are drawn perpendicularly to the lines of defence. The re-entering angle of the tenaille in Vauban could not be seen from the flanks ; to obviate this, a curtain of tenaille is traced parallel to the enceinte at 26 j^ards; the thickness remains 16 yanls, and the extreme profiles are at 5 yards i'roiii the Hanks; the counterscarp of the main ditch is tangent to circles described MOnKHN SVSTKM. HO.i from the salients with a radius of 30 yanis, and directod on tlie shonlder-anulos of the crests of the bastions. In order to prevent the besieger from crowning the covered way of the bastions at the same time as that of tlie ravelin, Vanban in his last tracings gave a greater salicncy to the ravelin. Connontaingno took its cajiital, equal to -pxths of the front. Now, 34 yards are taken off from the shouldci'-augle of the bastions, along the faces: an equilateral triangle described on this line, gives the ravelin. The ditch is 20 yards wide, and 6 feet less in depth than the main ditch. The ravelin is 20 yards thick. Its great saliency, which increases with the opening of the angles of the polygon, obliges the besieger to take it before crowning the covered way of the bastions, and its reduced thickness prevents him from establishing butteries on the terreplein to breach the redoubt. Vauban usually placed a redoubt in the ravelin ; instead of constructing it with palisades, Cormontaingne gave it a scarp and a ditch. The face of tliis redoubt is drawn parallel to that of the ravelin from the shoulder-angle of the crest of tiie bastion. Its ditch is 10 yards witle, its dejrth is 18 feet less than that of the main ditch, to prevent the besieger from attacking the ravelin at the gorge. Its gorge is obtained by bisecting the thickness of the ravelin at its extremities, and joining the points of bisection. It is therefore parallel to the curtain, and the staircases cannot be seen from any part of the covered way. The flanks of the redoubt are traced by marking oft" 20 yards on each face from the point where they meet the gorge, setting 16 yards off on the gorge, and join- ing. These redoubts must be carried too, before assaulting the bastions, since their flanks (18 yards long, and ai-med with 4 guns) can give a slanting and reverse fire on the breaches of the enceinte. The caponier remains as in Vauban. The covered way is also of the same width, 10 yards. The re-entering phices of arms arc larger, and contain a redoubt, wliich renders the attack l\y vive force impossible. This redoubt is traced Uy bisecting tlie re-entering angle of the countei'scarp, and joining the flanked angles of the bastion and ravelin together ; the line A B thus obtained gives the counterscarp of one face of the redoubt, the other is drawn from the salient places of arms before the bastion. The scai-p is parallel, and at 5 yards distance. The parapet of this face has a flank of 6 yards, to give a fire on the breach of the ravelin ; in order to mask the staircase at the gorge, the ditch of the ravelin is enlarged by tracing the counterscarp on the line that joins the extremity of this flank to the salieiSt angle of the ravelin. The ditch of the face t(nvards the bastion is not flanked — a great disadvantage. In Vauban's system, the besieger could establish batteries in the co\ered way of the re-entering place of arms, and breach tlio curtain tin-ouuli tlic sjiace inter- 300 MODERN SYSTEM. veiling between the tenaille and the flanks, called Trous des Tenailles, thereby obliging the defender to give a great extent to the interior retrenchments con- structed to prolong the resistance after the assault on the bastion. With this tracing, the trous des tenailles are masked. The strength of the redoubts obliges the besieger to advance carefully to the crowning of the covered way of the bastion, and compels him to run a fourth parallel across the slope of the glacis. The crest of the re-entering place of arms itself is described from the re-entering angle of the counterscarp as a centime, with a radius of 65 yards. The cr^'st of the salient place of arms is cut off perpendicularly to the capital, to give a banquette of 6 yards, in order to obtain a direct fire on the aj)proach. The glacis is also 50 yards wide. The traverses of the re-entering places of arms are traced, as in Vauban, 6 yards thick; along the faces there arc two more traverses, 3 yards thick: the crochets arc traced in Cremaillero to pre\ont the besieger from finding shelter in 'n'^^ i\-^- them, as was the case with the crochets of Vauban, but they arc exposed to enfilade. The passages are still 9 feet in the clear. To command the approaches when the ground presents hollows, as well as to form traverses or parados to protect the houses or other buildings in the rear. Cavaliers, or works with a great relief, have been employed, in any part of the enceinte. They are generally constructed of earth, and so organized as to form an interior retrenchment. When such a cavalier is to be constructed in a bastion, its faces are traced parallel to those of the bastion, and 34 }-ards within them : the ditch is 1 yards wide. The crests of its faces are parallel to, and at 10 yards from the cordon, and on the flanks at 34 yards from those of the bastion. The length of these is fixed l)y tracing the base of the exterior slope at 10 yards from the crest, and making it 28 yards long. To transform it into an intrenchment, a Coiipurc is made on the ilice of the bastion at the point where the breaches can be made. Its counterscarj) is drawn perpendicularly to the face of the bastion from the point where they are met by the faces of the ravelin produced. MODERN SYSTEM. :i07 Its scarp is parallel to, and at 10 yards from it ; its crest at 7 yards. To flank the ditch of tlio cavaliei', a traverse is erected on the rear of the coupure, perpen- diculai-ly to the face of the cav-alier, and 8 yards in the rear of the scarp of the coupure. Its crest is at 7 yards in rear of the cordon, and is 12 yards long. The length of the pai'apet of the coupure and that of its ti'averse ai'e limited by a line drawn from the extremity of the crest to the corner of the counterscai-p of the coupm-e — a method which conceals the staircase of the coupui-e from the terre- plein of the bastion, and insures a safe I'etreat. A coupure is also made in the face of the ra\elin : its counterscarp is detennined by a perpendicular drawn from the oxtruniity of the face of the reduit of Re-entering Place of Anns. Its ditch is 5 yards wide. 308 MODERN SYSTEM. (292). The commands and reliefs of tlie modem system are not absolutely fixed, every author adopting different dimensions. We give here those generally adopted in England, and refer for the discussion of this subject to Chapters XX. and XXII. The line A B represents the level of the gronnd. «i 5" ., rfei: l^ (293). The revetments are countersloping (See Section IV., Chapter XX.) The thickness at the top is marked in the profiles. That at the bottom is equal to ', of the height of the masonry. The counterforts have a length eqnal to the mean thickness of the walls. Tlie bottom of the ditch of ravelin is 6 feet above that of the main ditch, a disposition which enables the face of the bastion to defend it better, whilst the step formed at the I'etaining wall between both ditches presents a serious obstacle to tlie enemy advancing by sap along the ravelin towards the main ditch. The MODERN SYSTE^r. .-{OO eration, the arming of the batteries against the redoubt is a long and diiBcult task, and it is not to be done if the defence is still vigorous. It is better to breach the redoubt from the batteries established at the salient of the covered way of the ravelin, whence fire is directed tlirough aii opening made right through the whole thickness of the rampart of a face of the ravelin, either by artillery or by mine. Most engineers, however, recommend the use of the mine exclusively, more especially if the defence can still bi'ing guns to bear on the ditch of the redoubt. The lodgement at the salient of the ravelin being converted into a battery to counterbatter those guns, a zig-zag trench is carried through the ditch of ravelin to permit the miner to reach^ the escarp, when two galleries, a gi-eat and a common one, are driven through the ravelin up to the ditch of the redoubt. Tlio common gallery pierces through the counterscarp, then tlie escarp of the redoubt, and a iiiino lilowing down lioth re\etments makes a breach; the great gallery is 314 MODERN SYSTEM. then opened through the counterscarp, and serves as a passage to the storuiiiig l)arty. The redoubt being taken in tliis manner, the defenders are obliged to abandon tlio coupures of the ravelin, and the besieger at once forms his lodgment in them, by advancing across the ditch of redoubt, and blowing down the revetments. The advance from the fourth parallel, or from the demi-parallel towards the salient place of ai-ms of the bastion continues, and the crowning of the covered way of the ravelin is also extended. If the defenders have not abandoned the covered way of the bastion, it may be necessary to erect trench cavaliers as for the ravelin, and it is only when the covered way and its reduit are altogether left by the gai-rison that the crowning is carried all round the crest of the glacis. The breaching and counter batteries against the bastion are then constructed. In general, when the redoubt of I'avclin is taken, the defenders give up the redoubts of the re-entering places of arms, since the besieger finds no difficulty in occupying them, by blowing down the revetments and making a lodgment. Whilst the bastion is being breached, and its flanks are being silenced, the counter batteries at the salient of the ravelin have completed a breach in the face of the bastion. This breach is approached by zig-zags carried along the ditch of the ravelin, and that at the salient of the bastion by a descent into the ditch, or by a sap striking out of the ditch of the redoubt of the re-entering place of arms into the main ditch. Both breaches may thus be assaulted at the same time. When the bastion of attack is retrenched, the besieger, instead of assaulting the breach, forms a lodgment on it, and advances by sap right and left to the counterscarp of the retrenchment when the mine is employed, as was done for the redoubt of ravelin. Should there be a fiirther retrenchment, either the escalade or the mine ai-e had recourse to, or a battery is constructed in the terreplein of the bastion. It is admitted that under ordinary circumstances the siege would last from 23 to 25 days ; six days more must be reckoned when there is a ca\alier in tlie bastion. 315 CHAPTER XIX. SYSTEMS OF CCEHORN. (296). In 1685 Coehorii (460) pul)lisheil 3 systems of Fortification for aquatic sites, the first of which ho partially applied to the fortresses of Breda, Nimeguen, Naniur, Berg-op-Zooin, and Manheim. His metliod is called the improved Vutcli method, in opposition to the old method of Freytag (459). He borrowed much from liis predecessors, Durer (441), Freytag (459), Speckles (442), &c., but his inventive genius enabled him to suit the art to the ground, and his method is so thoroughly practical, that it is, even at the present day, admitted to be the best for aquatic sites. He insisted on the following principles. All masonry, except the exterior scarp of the orillon, must be well covered; tlie terreplein of the covered way, and the bottom of the diy ditches must be on a level with the water, so that the besieger, imable to excavate a trench without finding water, and therefore to construct lodgment and obtain cover, is obliged to liring a great quantity of material ; the outflanks should cover the flanks, and as these con- stitute the chief defence, long flanks should be prefeiTed to long faces; the garrison should be able to make sorties at all times, with safe means of retreat ; the outworks should be so isolated from one another, that the capture of one of them may not cause the loss of the others ; the strength of a fortress chiefly consists in the number of works well flanked; the enemy should be exposed everywhere to cross fire ; the advantages of wet and dry ditches should be com- bined ; the outlay may be reduced by making the ditches of different depths, and lastly, each polygon requires a special tracing (460). (297). In the first system Coehorn supposes that water is to be found at 4 feet below the surface. We give here the outline for a front of the hexagon. The front A B is equal to 3Q0 yards; the curtain CD =: 150 yards; the capital BE of the exterior bastion is 150 yards. The lines of defence ai-e drawn from the flanked angle E, F of the bastions to the extremities C, D of the curtain. The length of the faces is determined by describing ares of circles from the flanked 316 SYSTEMS OF CCEHORN. Fig. 567. angles as centres and radii equal to the lines of defence, so that E C =: E G, and F D z= F K. The chords G C, D K of these arcs, give the original flanks which will hereafter be modified. The faces of these bastions are not revetted, and the magistral represents the intersection of their exterior slopes with the water. At the shoulder angle a case- mated building or orillon is eonstnieted. Its long side k e, ineasui-es 38 yards, and is perpendicular to the face ; its short one is traced by producing the face fi-om Fig. 568. K K to 6 17 yai'ds. Taking K (^ =: 28 yards and drawing df parallel to h k and =z 28 yards, the line bf is the chord of the round face of the orillon, the face itself is an arc of 60°. For the gorge erect hc:^8 yards perpendicular to K o, and join fh. SYSTEMS OF CffiHORN. ;U7 The total thickness of" tho outer bastion, measureil at the level of the water is 15 yards. The escarp of the inner bastion is parallel to the lines of defence and 45 yards inwards, so that both bastions are separated by a dry ditcli 30 yards wide. The shoidder angle L, is found by producing tho inner gorge of the orillon S yards to q, and drawing q L perpendicular to the face. The main ditch is 48 yai-ds broad, measured at the salient of the outer bastion liorpendicularly to the face, and its counterscarp is directed on the shoidder angle \j of the inner bastion. Authors do not agree in the tracing of the flanks, they are generally too straight ; t he following method is more conformable to the plans of Ccehorn : on the part D of the original flank describe an arc of G0°, and 30 yards inwards describe a concenti'ic arc L P. The outer flank is not revetted. The curtain is connected with the inner flank by a brisiu-e D P, part of the line of defence, and it is revetted as well as the brisure and this flank. The teuaille is unrevetted, its flanks are ti-aced by measuring 280 yards on the lino of defence from E to R, and erecting R S perpendicular to that line : the faces and the broken curtain are on the lines of defence. The demi-gorges of the ravelin are 1 10 ysu'ds each, measured on the counter- scarp of the main ditch ; the faces are traced so as to form a salient angle of 70°. They ai-e not revetted, and as in the outer bastion, the magistral represents the intersection of the exterior slope with the water ; the thickness is 13 yards. The escarps of the inner ravelin are parallel to the magisti-al and 43 yai-ds inwards, leaving before them a dry ditc^h 30 yards broad. A harbour of 20 yards radius is cut in the gorge. The bastions are covered by earthen coimterguards 18 yards thick, whose length is limited by the counterscarp of the ravelin. Their ditch is 28 yards broad. The ditch of the ravelin is 36 yards wide, the covered way 24, the glacis 50. The re-entering place of arms is traced by setting 50 yards each way on the crests of the glacis and drawing the faces perpendicular to those crests. In front of the faces and at a distance of 13 yards is a loopholed gallery sunk in the glacis. Inside the place of arms is a reduit formed by a loopholed wall : its demi-gorges =: 25 yai-ds, and its faces are parallel to those of the re-entering place of arms. The covered way is separated fi-om the place of arms by traverses 18 feet thick. The details of this front differ so umch from those of the bastion system, that it is necessary to dwell a little over them. (298). Inner bastions. The > parapet of the faces and flanks of the inner bastions has a command of 22 feet ; it is 20 feet thick for the faces, and 24 feet for the flanks. The escarp of the faces is only 10 feet, and that of the flanks 9 feet above groimd ; so that the crest of the faces and flanks of the outer bastions. SYSTEMS OF CCEHORN. , ,., - cf euttr BasHcn respectively with 12 and 11 feet command, well cover the masonry of the enceinte. The curtain is also protected by the tenaille, its masonry rising only 6 feet ahove ground, whilst the parapet of the latter is raised 8 feet. The flanks of the tenaille, however, have only a command of 3 feet, so as not to mask the fire of the outer flanks. Outer bastion. The faces of outer bastions are secm-ed from enfilade by a bonnet .3 feet high and 45 yards long, their terreplein is only 5 feet wide. The crest of the curtain has a command of 18 feet only, so that there is a difference of 4 feet between the level of its terreplein, and that of the flanks. It has the in- convenience of interrupting the communication, and exposing the higher rampart to the enemy's jjrojectiles. This difference is not represent ^ HS 5; K ro 2. -^il c 5 p- P 7: SYSTEMS OF Ca^HORN. 331 tlie salient of upper ravelin ; 6, 6 to fire on the flanks of the front of attack when an opening has been made tlirough the counterguai-ds, and destroy the casemate of the or i lion ; 7, 7 to cut tlu'ough the faces of the lower bastions, destroy the draw-bridges and walls of the dry ditches, enfilade the flanks of the tenaille, destroy the casemates under the brisuro, and finally to breach that brisure ; 8, 8 to ricochet the faces of upper bastions after the destruction of the lower faces, take the upper flanks at reverse ; and destroy the casemated battery of the orillon ; 10, 10 to take the upper flanks at reverse, and destroy the traverses which the gan-ison will throw up to cover them. On the 17th, four descents into the covered way have been effected; the besieijers debouch from the extremities of the re-entering places of arms behind the traverses, and are either blinded or covered by epaulments of gabions, fascines and earth. The passages of the ditch of the ravelin and of the counterguards also begin. On the 18th, the passages are completed, the besieger occupies the faces of the lower ravelin, erects an epaulment across its dry ditch to the salient of inner ravelin, and by zig-zags cut in the parapet of the lower faces, arrives opposite the breaches made at the extremities of the upper faces ; the counterguards are occupied at the same time, and similar zig-zags lead to the points where the passages of the main ditch are to be made. On tlie 19th, the inner ravelin is taken, and the batteries continue their fire to facilitate the construction of the passages. On the 21st, the passages reach the faces of the lower bastions, and as the enceinte is breached on the faces and flanks of bastions and at the brisure of the curtain, the assault may be given on the 22nd. In this attack, it has been admitted that the earthern parapets may bo destroyed by shells filled with powder. Bousmard and even Cormontaingne were of opinion that, in two or three days a breach could thus be made through a face 18 yards thick. The projectiles in destroying at the same time the galleries, caponiers, and the casemate of orillon, niin the defence of the dry ditch, and the dispute on which Coehorn strongly relied to proti'act the siege. He contested the possibility of cutting with artillery an opening through the lower faces On that hypothesis it is clear that the attack would proceed much more slowly, since it would become necessary to occupy these faces, and establish breacliing batteries on them, or cut an opening with the mine. The counter-mines prepai-ed in the ravelin and bas- tions, would then delay the besieger on these faces, and the siege might last 36 or 40 days, but the improvements in prtillery leave no doubt now as to the possibility of cutting an opening through those thin faces with live shells. 332 CHAPTER XX. PERMANENT FRONT. SECTION I.— Tracing of Fortkesses. (305). Great importance has hitherto been attached to the construction of regular fortresses. Vauban himself, whenever he could do so, adopted a regular polygon for the base of his tracing, and such places were called " royalea." The perfect equality between every fi'ont, far from being advantageous, is a serious in- convenience. Every bastion is in fact equally liable to attack, and if any addition, such as retrenchment, coimterguard, &c., be made to one front, the same outlay must be made for all of them, otherwise the enemy will attack those fronts the strength of wliieh has not been increased. The onl}' advantage of a regular tracing is to enclose a greater interior space by a given number of sides. A-^_^J\ -A-___._.A If wc now consider a place in which several fronts are traced on the same sti'aio-ht line, we readily perceive that the angles of tlie polj^gon are only expose d to attack, since, the prolongation of the faces of the intermediary bastions falling on the ravelins, the enemy cannot enfilade them. These bastions become still less exposed when they are {)laced in a more and more i-e-entering position by the addition of works before tlio exposed angles ; and even supposing the enemy attacked them, he would not find room at the salient of tlie covered w.iy to establish his batteries. This property of fronts in straight lines seems to have been overlooked by ancient engineers, and although one of them, Fabre, proposed in 1629 to construct fortresses on squares, the sides of wliicii sliould be divided into several TRACING OF FORTRESSES. 333 fronts, tlioroby offering only four bastions of attack, yet it is only Corinontaingiio wlio succeeded in drawing attention to this sulijcct. lie recommends the construc- tion of fortresses on a triangle, somewhat of this form, the small angle of which is truncated and rei>laced by a citadel. In this manner the enemy will have only two bastions to choose between for attack, and the outworks, with the exception of the covered way and the glacis, may be dispensed with on the fronts occupying the straight lines. This method, however, implies a place of great extent, and canuot be invariably adopted, especially as the shape of the town greatly influences that of the fortifications, but it is a standard at which we should aim. It is impossible with fewer than nine fronts, excellent with from twelve to twenty-four, and perfect when one, two, or even the three salients can be protected by serious obstacles, such as inundations. The presence of rivers has also a great influence over the general outline. If the town is traversed by a large river, it is advantageous to rest two salients on it. The enemy will then find a difficulty in devclopuig his attacks on them, inasmuch as he must occupy both sides ; the other fronts being traced on oblique lines, there would be but two bastions of attack situated on aline perpendicular to the river. This disposition is certainly pi'eferablc to that in which the river intersects a straight line of the perimeter, since the latter can only protect a space 334 PERMANENT FRONT. equal to its own width, and requires particular dispositions of detail, as high quays of masonry acting as flanks, and parapet bridges acting as curtains, together with strong iron gates to close the arches, &c. Small rivers are more precious to the defence, as capable of producing inunda- tions on which to rest several fronts. The triangular form is particularly applicable to those towns situated at the confluence of two rivers. Lastly, when the place is all on one side of the water, the greatest possible imber of fi-onts is traced along it, and the rest of the perimeter is bent into a numb convex outline SECTION II.— Tracing of a Front. (306). AVhen a place is to be constructed, the fii'st thing to determine is the polygon to be fortified. It is an exterior polygon when it surrounds the fortifi- cations of the enceinte, and an interior polygon when it surrounds the town within the fortifications. The place is said to be fortified inwards or outwards, accordingly as the outline of each front is traced on the side of the exterior or interior polygon. Some ancient engineers recommend fortifying outwards, because the interior side really limits the fortified space, and is rendered compulsory by the form of the town ; but Vauban, and with him modern engineers agree, prefers the exterior side, because bastions being the chief parts of the defence, their salients must be advantageously placed on the ground, and besides, as they must be flanked within easy range, it is necessary that their position be settled before fixing that of the flanks. Both principles are correct ; and it is only by due attention paid to the exterior as well as to the interior side, and therefore only after a few preliminary essays, that the engineer will hit upon a good outline. (307). Since the various fronts of fortification have not the same length, it follows that the formula laid down for their tracing cannot be always applied. With a front of 360 yards the formida giving con-esponding curtains, flanks, &c. sufficiently supplies the necessities of defence : but when the iront is less, the TRACING OF A FRONT. -535 curtain becomes too small, and as this reduction is not l)a.sed upon principles of defence, the usual relief cannot permit the flanks to defend the ditch in front of that curtain. Besides, it may be impossible to trace a front perfectly symmetrical. It is therefore necessary to record the principles on which each ]iart of a front should bo constructed. . (308). The relief is the first consideration. It is now admitted that to prevent escalade a scarp wall should bo at least 30 feet high, of which 8 feet may be above the ground, since the glacis covering the masonry has usually that command. Tiie crest of the parapet can barely have a command less than 16 feet, 3 feet for the dip of the superior slope, 5 feet for the exterior slope, and 8 feet for the part of the escarp above the level of the ground. Should any outwork exist between the enceinte and the glacis, a far greater conunand must be given to the enceinte, 20 feet, 24 feet, or more. A small command has the serious inconvenience of giving small remblais, which it becomes diflieult to equilibriate with tho deblais. (309). The greater the relief, the stronger the profile, but the greater also the dead angles ; and although the ditch may bo raised before the cm-tain, and deepened before the bastions, it is not always practicable^ The flanks, as we have said (94, 275), must afford a -view of the ditch before the middle of the curtain, and as their superior slopes are at i, the distance between their crests is twice 38 X 6, or 456 feet. As, however, it is quite sufficient to see 2 feet above the bottom, the distance may be taken at 420 feet, which deduction made on the two parapets, with their slopes 24 feet each, leaves 372 feet, or 120 yards, in round numbers, for the minimum of tho cm-tain. The maximum should not exceed the range of the new musket : but the cases in which such a curtain would be required are exceedingly rare, and it is usual to keep nearer to the minimum. (310). As for tho jianks, they must defend the salient of tho bastions: the old engineers had fixed the maximum of tlie lines of defence at 250 yards, and as the old musket could scarcely cari'y that distance, special weapons, called wall- pieces, were necessar}'. They may now be dispensed witli, and the lines of defence increased to 300 yards. Some engineers say 500 yards or more ; but can a soldier see a man in the ti-enches at that distance ? The direction of the flanks perpendicular to the lines of defence is not so good as that given by Vauban, because the angle of the flank is too open to permit the defence of the foot of the ctu'tain ; therefore the French engineers now trace the flanks, forming an angle of 99° 30', with the curtain ; a construction very nearly coinciding with that of Vauban. ^ The space at disposal and reasons of economy may limit theu* length. When destined to flank bastions not exposed to attack, they may answer their purpose with two guns, and their length may be reduced to 15 yards, more especially when 6A6 PERMANENT FRONT. they cannot command a view of the ground the enemy can occupy. Such cases seldom occur, and as the flanks are the most essential part of a front, there is advantage in making them long; but 50 or 40 yards, dimensions adopted by Vauban and Cormontaingne, are quite sufficient, since they outbalance the space the enemy can dispose of at the salient of the covered way. (311). The faces of the bastions should be traced on the lines joining the extremities of the flanks to those of the curtain ; in this direction the flanks are said to be " rasant," whilst they are " fichant," when they ai'e mot by the faces produced. It is clear that " fichant flanks " are fiuilty, the part left between the face produced and the curtain being useless. When the faces are fichant on the curtain, they are better defended, because the flanks can readily discover the breach, which can even be seen at reverse, and the curtain itself may, with oblique embrasures, contribute to their defence ; but they become less uiulincd upon the fi-ont, and may the more easily be enfiladed by the enemy. The length of the faces necessarily depends upon that of the curtain and of the line of defence, a small curtain permitting the construction of large bastions well fitted to receive interior roti-cnchmcnts. When the front is not exposed to attack, there is some advantage in lia\ ing a long curtain and short faces, the former being always less liable to enfilade. (312). The consideration of the flanked, and of the diminished angle, may furtlier induce the engineer to modify the tracing. As a rule, no flanked angle should be less than 60°. As for the diminished, Vauban and Cormontaingne's constructions usually make it equal to 181°. This limit should be maintained, because the field of a gun firing through an embrasure being very neai-ly the same, 20° at the utmost, the first gun of the flank can see tlie escarp both of the curtain and the opposite bastion ; and a gi-eater opening, besides being unnecessary to the defence, gives a greater depth to the fortification and increases the amount of masonry. (313). All the preceding considerations must be weighed before definitively adopting a tracing, and several essays will be found necessary before harmony can be established between each part The ground may vary, symmetry may not bo possible, the relief, or the length of curtain or other part, may be fixed, a prion, and the tracing on condition, as it is termed, becomes a problem which a knowledge of Euclid and of the foregoing principles will render easy. To illustrate how the dimensions of fronts may be obtained from conditions, let us construct a front such that the escarp of the curtain may be seen from the Fig. 592. INTERIOR WORKS. ;^37 flanks within 3 feet of its foot, tailing the relief of one Hank cqiial to 40 feet, of tlic other to 34 feet, the wail of the escarp being 30 feet high, and the liness of defence 280 yards long. Take A B for tlie bottom of the ditch in front of curtain, and draw a line parallel to it, and 3 feet above. On this line take any point C, and through it draw two lines inclined at ~ to D and E, respectively 40 and 34 feet above AB. Finish the construction of the parapets, and F G will be the length of the curtain. Now, takefcf as the length in yards, and draw c/ M,/N inclined on fg at 4 for an hexagon or liigher polygon (J- for a square, f for a pentagon), and taking ff jSI =f'N— 280 yards, the front required will be M N. SECTION III.— Inteiuok Works. (314). Cavaliers are works of great command constructed on the terrepleins of bastions or curtains. These works should not be commanded b}' the parapet of the enceinte ; there- fore they are only erected in full bastions, the parapet of which they command b}' from. 2 to 4 yards. They are intended to overlook hollows which an ordinary command cannot bring to the vioyf of the defenders ; to cover the flanks from reverse and the enrt.ain fi'om enfilade fire; to prevent the besieger ft-oni making a lodgment in the breaches, and to further extend the action of the fortress, even from the very beginning of tlie siege. But . tliev have the very serious incon- 338 PERMANENT FKONT. veniencc of confining tlie si).ice on which the garrison has to defend the breaches to sucli a narrow strip tliat an active defence is no longer possible : their great command is not favourable for the defence of the breaches which are so ncai- ; and they occasion great outlay. We have seen one of them organized as an interior retrenchment in the modern system, and to the defects enumerated above we may add that it has dead angles in its ditch, and that the communications with the bastion are precarious. Cavaliers are therefore recommended merely to command hollows, which the besieger might tuni to advantage ; if possible, they should be erected in the bastions collateral to the one attacked, and leave at least 12 yards terreplein clear before them. Their faces and flanks should not be parallel to those of the bastion, to avoid enfilade by the same batteries. When their scarps are revetted they should be constructed still more in the rear, because splinters may seriously inconvenience the defenders of the bastion. (315). Cavaliers have occasionally been erected on the curtains with a conmiand of fi'om 2 to 4 yards over the parapet of the enceinte. They form an excellent position for heavy guns, with which much damage can be done to the works of the besieger, whilst they remain almost safe against enfilade. They are also extremely useful for the establishment of casemates, and by the addition of small flanks they may contribute to the defence of the breaches more efficiently than bastion cavaliers. It is usual to revet them, and to trace their escarp 15 yards in rear of the crest of the curtain ; a thickness of 22 yards is suflSciont. They are not fre- quently constructed because they hinder the communications, yet they may be seen in some places covering gates or posterns. (316). Interior retrenchments are destined to give a garrison the means of vigorously defending the breaches without exposing the place to be carried by storm. When the fortress presents points of attack strongly characterised, tiiese works may be permanently organized ; but as in general the defenders cannot know previously which front will be attacked, it is usual to defer their construction INTERIOR WORKS. 839 till after the siege has begun. Many tracings have been employed, but the chief are the tenaille, the bastion, and the straight lino. They may rest on the faces, or the flanks, or occupy the gorge of the bastion. Those resting on the faces may be turned by the breaches which the besieger may make at the shoulder-angle ; those resting on the flanks may also be turned by the breach made in the curtain through the opening of the tenaille ; and as for those constructed on the gorge, they cannot bo turned easily, yet as the flanks can no longer defend the collateral bastions the besieger may easily take them by escalade or mining, and the retrenchment becomes useless. The tenaille tracing is preferred for nai-row bastions : the ditch has no direct defence, but as there is plenty of room iii li-ont for the active defence of the breach, it advantageously replaces the cavalier retrenchment. When the bastion is wide, the bastion ti'acing is better, as giving a greater development of fire on the breach, and as flanking its own ditch. It is to l)e found in some of the foi-ts constructed at Lyons. When such retrenchment is constructed at the gorge, or rests on the curtains on tiie rear of the teiKiilles, it becomes an excellent work, z 2 340 PERMANENT FRONT. capable of a good resistance, and has the only inconvenience of being exposed by the fall of the collateral bastions left without defence. Sometimes the retrenchments are made in the same Ijastion. A more simple outline is that of a straight parapet along the gorge. It leaves room in front for the defence of the breaches, and does not enci'oaeh on the in- terior of the place ; it is fiirther from the breaches, and therefore defends them better, and the two lateral bastions may be made to contribute to its defence, by merely lowering the parapet of their flanks when the besieger prepares for the assault. On the other hand, it diminishes by half the length of the flanks ; but this is not very serious, since the flanks of the bastion of attack have only to pro- tect the collateral bastions against escalade, and the inconvenience may be obviated by interrupting the ditch and parapet close to the flaidis ami completing them at a later period of the siege. On account of its simplicity and of the little outlay it necessitates, this retrenchment at the gorge is advocated by many engineers. Whatever form be ado]5tcd, the parapet should have a command over the bastion: the ditch should be at least 10 yanls wide, the escarp G or 7 yards INTEKIOU AVOKKS. 341 high, and tho counterscarp not less than 5 yards. Instead of constructing posterns and ramps, it is better to cut a passage througii tlie parapet and to cover it by redans of stockades and traverses. (317). Casemated retrenchments have been proposed by Carnot (412), to re- place the various disjiositions which we have just enumerated. They consist of a wall 36 feet high and 9 feet thick, erected at the gorge of tho bastions, and pro- vided with two rows of loopholes, the upper for musketry, the lower for small mortars of a peculiar description. Behind tliis wall is a ditch 20 feet w'ide, and on the rear of it stands a casemated battery formed of a scries of open arches, having their axes parallel to the capital and containing two mortars each. Their platforms arc on a level with the place in order to facilitate the communication, i .^_^,«g^?^ and 12 feet above the bottom of the ditch, in order to protect the gunners from the splinters of the shells that may fall between the batteiy and tlie wall. In front of the wall, a ditch 12 feet deep, rises by a gentle slope to the level of the terreplein of the bastion, to permit the garrison to make " oifensive returns."' In rear of these batteries, Carnot proposes a parapet without revetment and also without flank defence, but it is evidently useless, since tho besieger, once master of the wall, finds no obstacle in spreading along that parapet and scaling it. Most modern engineers therefore abandon this parapet, and those who place reliance on the vertical fire of tho small mortars, who believe it possible that the arches can resist the concussion of a continual fire and the fall of shells as well, and who trust that the men at the loopholes will not be seriously inconvenienced by the proximity of tho battery, (and tliey are exceedingly few in France who do so,) recommend this sort of retrenchment. General Dufour, among others, recom- mends the following improvement. 342C ? PERJIANENT FRONT. The wall, only 21 feet high and 6 feet thick, has only the upper row of loop holes destined for musketry, and is connected to the curtain by two flanks. The coupures before them being directed towards the extremities of the flanks of the redoubts of ravelins leave no opening to the enemy to fire through and breach the wall, and they may be dehhyed during the latter part of the siege only. A ditch 30 feet wide runs before the wall, and separates it from the terreplein of the bastions. The easematod battery is 6 yards in rear, with arches 17 yards long supporting an earthen parapet. One mortar only is allotted to each ai-ched casemate, the height of which remains 15 feet as with Carnot, but the width measm'es 18 feet instead of 24. The upper part is widened on the outside, to resist the con- cussion caused by firing. There is no doubt that this retrenchment would be excellent if the wall could remain uninjured till tlic assaiilt is given to the bastion. In several fortresses in Germany these interior retrenchments have been organised permanently on a different principle. A casemated building is constructed at the gorge, the lower story on the same level as the natural ground, defends a ditch in front by musketry, the second floor on a level with the teireplein of the full bastion contains artillery. The building is connected with the curtains by a revetted parapet, and a platform for artiller}- acting as a cavalier is constructed over it. The besieger, it is pi'esumed, will be obliged to employ the mine exclu- sively, and the defence has pro^^ded for this eventuality by the establishment of a system of galleries. - SECTION IV.— Escarps. (318). In order to increase the strength of the enceinte, and provide the ditch with a grazing fire, engineers of the 16th contmy employed the faussehraie, or a second enceinte of small command before the curtain, the flanks, and some- times the bastions, but it was soon abandoned, because the splinters from the escarp beliind it, reiidei- it dangerous for the defenders ; it may indeed be called a ESCARPS. Kio. «(I3 I " shot trap " for the projectiles of the enemy, it is easily enfiladed and oven plunged, and as it divides the whole relief into two stories, it facilitates the escalade. The artillery does not sufficiently command the glacis, and if its relief be increased, that of the inner enceinte must also be augmented, and it becomes too great. Yauban set it aside and replaced it by the tenaille. (319). Another disposition of the enceinte generally found in ancient fortresses, and likewise abandoned by Vauban, is the chemin des rondes. It is a sort of passage or berm at the top of escarp before the foot of the exterior slope, protected by a small wall fonning a parapet, and used by the officers as a path to go their rounds without crossing the ditch. This chemin des rondes enables the defenders to see the foot of tlie escarps at close range, to repel the enemy who lias succeeded in placing his sealing ladders, and to give a double amount of musketry fire on the ditch and the outworks. On the other hand, if it has a sufficient command to give a sight of the glacis, its parapet is exposed to artillery and is soon desti-oyed, whilst if it is kept low, so as to fire only into the ditch and the covered way, it is exposed to enfilade all along the faces of the bastions. Its narrowness prevents the garrison fi-om mustering in force to repulse the escalade, and when the breach is made and the assault given, the enemy spreading all along it, turns the interior defences. Modern engineers have abandoned it, but its good properties may be restored by merely tracing it before the curtain and the flanks in the following manner. The enceinte being traced, and the crests of the parapet fixed, the magistral of the curtain and of the flanks is brought ten yards forwards, and that of the faces of the bastions is produced, till it meets this new flank. Between the new magis- tral and the exterior slope, a chemin des rondes with a banquette is organized, the terreplein of which is kept 6 feet^ below the cordon, and communicates with the rampart by a passage at the exti-emity of each flank. Such construction reduces the outlay of masonry, since the magistral is shorter, and the tliickness of the escarps may be reduced on account of the parapets being more distant. The 344 PERMANENT FRONT. enfilade is no longer apprehended, inasmuch as the escarp of each face at the shoulder angle is capable of heing easily transformed into a traverse. The crest of the parapet, it is true, should have a sufficient command over the magistral not to inconvenience the defenders in front, and this may necessitate too great a relief, but it may be obviated by lowering the ditch and the magistral of the curtain and flanks, and maintaining the former command of the crests. (320). Escarp revetments. — Some places are found, the enceinte of which differs from that of an ordinary field fort only by its greater relief. It is economy alone which thus induces a garrison to dispense with a revetted scarp, for the j)alisades and fraises destined to prevent the escalade, are soon destroyed by the first ricochet batteries of the enemy, and the place is then exposed to attacks of " vive force," Such a disposition should only be resorted to when the ditches can be filled with water, as will be explained hereafter. The I'evetment of the scai-p must be sufficiently sti'ong to bear the pressure of the parapet above, and to present some resistance to the fire of distant artillery. It would be mere waste to give it an extra thickness, as often recom- mended, to resist breaching, because the breach is always ready before the descents into the ditch are completed, and the increase of outlay entailed hy that extra thickness, is attended only with the trifling result of obliging the enemy to fire a few more rounds. (321). Two sorts of revetments are employed, solid and counter-arched. The former is called Sifull revetment when the wall is earned up to the superior slope of the parapet, and a demi revetment when it is raised up to the level of the ground .only. The full revetment is exposed to artillery from a distance, and the lireacli will bring down the whole parapet,* whilst the demi-revetment is not so exposed, and the breach will only bring down part of the parapet, advantages which have induced Cormontaingne and his successor to give it the preference ; but many riie small wall, 3 feet thick at the top, is callcl '• tabWttc." ESCARPS. Fio. 606. 345 engineers will contend that it is an error, because the scarp is exposed to escalade, and they prefer the denii-revetmcnt with a chemm des rondos, as possessing the advantages of both. According to its shape, tlic solid revetment is called leaning, rectangular, countersloping, or slojjing. The leaning one, the best in theory, is chiefly employed for the interior slope of the ramparts. FiQ. 608. r The m'towr/7(/«r is not now emplMvcl, Ikhuusc a slight sinking in the founda- tions Ijrings it out of the vertical, as may be seen at St. Omer and other places. Fifi Roq Fig. 610. The counter-sloping, either with, an interior slope or with steps, is not better than the sloping one when the counterslope is ", but becomes superior to it with a loss steep slope ; it is a good revetment and is preferred to others by many engineers, yet it re<|uires more masonry. 346 PERMANENT FRONT. For scaq) walls exposed to the action of the sea, this profile has been recom- mended. At Cadiz it has answered very well. Vauban adopted the sloping one. Before his time scarps were frequently at f and j-, because it was erroneously believed that such an inclination makes the balls glance off. Vauban made them at f, and Cormontaingne at -• It has, to a greater or less degree, the inconvenience of requiring frequent repairs; it suffers much from exposure to weather, the joints holding the wet and harbouring plants, the roots of which sooner or later destroy the masonry. Modern engineers have reduced the slope to V'> and French engineers now adopt V'- For the thickness, the dimensions of Vauban, 5 feet at tlie top, and 5 feet + -r at the base, H being the height of the scarp, have not been preserved, although none of the walls he built ever gave way. It was too much for counterscarps and low walls, but it was not sufficient for very high ones. In his f\ill revetments H was measured from the bottom of the ditch up to the terrepleiu of i-ampai-t, the small wall above it being only 3 feet thick. Cormontaingne gave a mean 9 H thickness of — tt ; but it is now admitted that a wall, the mean thickness of which 40 XT is — will possess sufficient stability to resist pressure in any soil. Belidor, Coulomb, Prony, and other engineers, have calculated formula for the thickness, which it is not om- province to investigate. At present the thickness .r of a rectangular ^v!dl is calculated by x =: -865 (H + h) Tan. — y - , in which H re- presents the height of tlie scai-ji, H that of the exterior slope, « the angle formed by the exterior slope with the vertical, p the weight of a cubic y.ird of earth, pf that of masonry. 20 For a counterscarp, h =z 0. When the wall is sloping at -y the thickness H ESCAUP3. 347 (322). Counterforts, or interior buttresses are frequently constructed to give more stability to the wall by their wei-jht, and enable it to resist more easily the shock of distant artillery. The pressure of the earth on their interior surface is a force which also resists the forward motion of the wall. They have been made dovetailed {T\g. 612), rectangular (Fig. 613), and diminished (Fig. 614), _n_ ^^ 3 the two latter forms being prefcniljk', IjLeauso the bond of the counterfort with the wall is better established. Vauban used to place them 16 or 18 feet apart; their length, E H, was 3 feet less tlian the thickness of the scai-p at its bottom, their width C D at root, one foot more than their length, and their tail, A B, narrower than the roots by 4. He had not an}- for the counterscarps. At present H the foUowinn; dimensions are recommended H 2 H root. distance, 15 to 18 feet. (323). By constracting arches from one counterfort to the next, the thickness of the scarp may be diminished, because the whole pressure no longer bears on the front, and as the arches will support the parapet after the fall of the wall, the broaching will be seriously hindered. The name of hollow or to nnter arched 348 PERMANENT FRONT. rev^etment has been given to this disposition wliich is both excellent and econo- mical, more especially for high scarps. In the first disposition, represented with a scarp 30 feet high, tiie piers will be 5 feet thick, 18 feet long, and 18 feet apai-t from axis to axis. The arch is 3 feet thick at the top, forming a vault 21 feet high in the clear. The front wall ^^^^m^fMf, la u needs only be 5 or 6 feet thick. The earth falling at its natural slope, will leave an empty sjjace to that door, being pierced thi-ough the jiiers, the defenders will have galleries ready made to employ mines against the breach, and Ioo})holes being cut in the fi'ont wall, the ditch will receive a grazing fire. In another disposition the galleiies are left empty, and are closed at the back by a circular wall ; they are ventilated, as shown by the diagram, and become real 'm~)(^ ^r%\/^v^/«v\/»)/~^/ wy \)/ \)A'^ casemates. It is advisable to leave at least 4 feet of earth over the arch, to give to this a thickness at least equal to ] the radius of curvature, and to pierce the loophooles at equal intervals measured on the outside, because the enemy cannot guess at the very place of the piers, and thereby breach more easily. Another system of hollow revetment has been constructed with a second wall behind the first, the arches being parallel, instead of perpendicular to the front ; but the pressure of the vaults beai's on the front, and renders brcacJiing less difficult. ESCARPS. Kio. 620. 349 i (324). The independent scai'p wall consists of a wall 3 feet thick erected at the foot of the exterior slope, and when it is breached the parapet cannot fall. / It is loojihok'd and provided with a banquette. Sometimes it is arched in the rear to covor the men from enfilade, and to miin additional stroneth. The height should not be under 20 feet. It is often seen in Germany, where the advantage claimed is, that it is less exposed to escalade than other revetments of greater height, since the enemy, arrived at the top, will require fresh ladders to descend. This ehemin-des-rondes is greatly improved by the construction of traverses jilaced at intervals of 50 or 60 yards ; their loopholes enable the defenders to fire at the salient, and as they join the covering mass, they prevent the enemy lodged at the salient to enfilade and plunge the whole. 350 PERMANENT FRONT. Fio. f)2'l Jj_ -? (325). With regard to the foundations, Vaulian used to make them 3 feet deep, with a retreat of 1^ feet in good soil, but these dimensions must be increased whenever the soil is compressible. At Ypres, for instance, some foundations were made 17 feet deep. Sometimes to prevent the revetment fi-om sliding outwards piles of wood have been buried or spui's of masonry built at the foot of tlie foimdations. Fio. 624. Fig. 625. In aquatic sites, where ditches are usually very largo, a mass of earth may be advantageously left before the foot of the escarp to servo as a prop to the spurs of masomy. Fio 626. SECTION v.— Of the Ditch. (326). The ditch is .destined both to form a serious obstacle to the further progress of the besieger, and to furnish the deblais for the construction of the rampart and parapet. The greater its width and depth, the greater the obstacle ; but reasons of economy and the necessity of equalising the deblais and remblais impose limits. THE DITCH. 351 In genoral, the wkltli at the salient of the bastion is 30 yards. At that point the counterscarp is traced on the arc described from the salient of the escarp as centime, and it is afterwards fixed so as to admit of a sight of the ditch fi'oni the whole flank, the width thereby increasing from the salient to the curtain, unless the flank be less than 30 yards, in which case the counterscarp is better traced parallel to the magistral. It is preferable to increase the depth of the ditch rather than its width, because by this the enemy is delayed longer in constnicting his descent gallery. Some engineers recommend it to be made narrow and very deep for that reason, and also because when the depth is such that the batteries established on the crowning of the covered way do not afford a view of two-thirds of the escarp, the besieger is obliged to erect his breaching batteries in the covered way itself, or to have recourse to the mine, two dangerous and uncertain operations ; but narrow ditches have the serious inconvenience of being liable to be filled by the debris of breaches made at the escarp and counterscarp. Therefore, these are not made less wide than 25 or 20 yards. That of the ravelin may vary from 15 to 13 yards. When the widtli is settled, the depth is found by the conditions of the deblais, and we have seen that it should be such as to leave at least 30 feet to the revet- ment of the escarp. The counterscarp should always be revetted ; it would not otherwise be a serious obstacle, and the higher the better ; but some reasons of economy not unfrequently oblige the revetment to be made as low as possible, viz., 15 feet. When the terrej)lein of the covered way, the position of which is determined by special considerations (Sec. I. Chap. XXII.), is more than 15 feet above the bottom of the ditch, the revetment may be maintained at 15 feet, either by making the ditch slant towards tlie escarp, or, what is better, by joining the masonry to the tcrreplein by a slope. (327). In order to carry off the water arising from springs or rains, it is usual to give to the bottom of the ditch a slope, both from the escarp and the counterscarp to the middle, where a small ditch, 4 feet wide at the top, 2 feet at the bottom, and 3 feet deep, called cunette, is excavated. When there is much water the cunette may be made larger and deeper, and it forms a fresh obstacle. It should have a sufiicient fall to drain the ditch o?i to a well sunk for the purpose, or to some low ground away from the fortifications. // ^ I CHAPTER XXI. ADDITIONAL WORKS. SECTION I.— O0TWOHKS. It is a general rule that all the outworks consti-ucted on a front should be flanked by the enceinte itself, that their gorge should be open, that their ten-eplein present no cover for the enemy, and that their combination be such as to admit of a successive defence. (328). The ravelin is most frequently employed, although it by no means forms an indispensable part of a front, especially in uneven ground. The effectiveness of that work increases with its saliency, but not indefinitely, because its breach must be defended by the bastion within easy range, and with a great saliency the enemy can breach the enceinte from a greater distance. For these reasons it is advisable to limit to 200 yards, the maximum distance from its salient to the crests of the enceinte. The flanked angle will be 60°, the minimum, because a larger angle would bring the re-entering places of arms too forward, and the glacis of the raveUn would not be well flanked by the faces of the bastion. This last consideration necessitates a further reduction of the saliency when the bastions are small, because it is desirable that 50 yards at least of their faces should not be masked. Several engineers have greatly modified this outwork, especially with the view of closing the opening of its ditch on the enceinte ; and we shall examine their construction further on. At present we confine ourselves to the ravelin of the ordinary bastioned front, such as we find it in the modern system. Some engineers object to this ravelin, that the narrowness of its terreplein leaves no room for the employment of mines in the defence, and renders offensive x-eturns very difficult, whilst the besieger can find sufficient space to construct his batteries. Although an unrcvetted ravelin answers all the requisites of exterior defence, yet it is better to revet its scarp, because the iiieniy being obliged to enter by a OUTWORKS. 353 hroach, tlic defenders will find it easier to repulse the assault. The scarp need not bo so Iiigli as the enceinte, and its minimum may be fixed at 15 feet. The ditch, from 12 to 20 yards wide, slopes towards the main ditch to can-y tlie water off, and at the same time exposes itself to views from the bastion. The connnand of the curtain on this work should not be less than 3 feet (329). The gorge of the ravelin may be organized so as to form a sort of retrenchment fi-om which the gaiTJson can make offensive returns, and oppose an extended line to the necessai-ily narrow front of the enemy, but it is preferable to construct a reduit on the principle of the modem system. The faces are kept parallel to those of the ravelin, and the flanks arc made 20 yards long. A revetted escarji of 1 5 feet is necessary, but the counterscarp is better left unrcvctted, and even sloping as a ramp towards the salient, to enable the defenders easily to attack the lodgment of the besieger. The width at the bottom of the ditch may vary from 12 to 15 feet. This outwork should possess a sufficient command over the i-avelin to enable the men to fire over it on the glacis of the collateral bastions ; but as this command might cover the terreplein of the ra\elin from the view of the enceinte, it will be proper to adopt a command of 11 feet only. The magistral is kept in a plane with the terreplein of the ravelin, and the interior of the work is maintained as low as conveniently can be. The saliency of the reduit must be sufHcient to enable the faces of the bastions to flank its ditch, which is generally 12 or 15 feet above that of the ravelin. Masks of earth, in the shape of a glacis, are erected both in the ditch of the ravelin, and in that of the reduit to close the trouees ; they are placed near their gorge, and are kept at such a height as will prevent the escarp from being breached. (330). Coiipures along the faces of the ravelin prevent the enemy from turning the re-entering places of ai-ms of the covered way, defend the breach of ravelin, permit oSensive retm'ns, and secure the retreat of the defenders ; therefore, they are frequently adopted, althmigh their ditch is only flanked by the reduit. Their command is the same as that of the reduit; their ditch, about 12 feet above that of Kio. 627. this w(irk. will slojie towards the escarp of the ravelin; the escar]), aljout 12 feet A A 354 ADDITIONAL WORKS. high, and the counterscarp not less tlian 9 feet, should be revetted. When the depth of the ditch of the ravelin is such that there remain 15 feet of escarp, it is better not to close the ditch of the coupiu-e, as it is done in the modern system. It must be borne in mind that the enemy established at the salient of the covered way of the ravelin can see the interior of the coupure near the gorge. Coujjures may occasionally be made in the reduits themselves. In Germany we find ravelins that, instead of the redoubts of Cormontaingnc, are provided with bomb-proof block-houses or buildings ha\ing casemates for artillery, and loopholes for musketry. A loopholed wall connects them with the gorge of the ravelin, and a ditch prevents the enemy from approaching. Prussian engineers deem it impossible for the besieger to establish batteries against this I'etrenchmcnt, and thoy adopt a similar disposition for bastions. (331). The tenaille is an accessory that may be dispensed with when tlicre is no outwork between the enceinte and the glacis, and replaced by a traverse of earth masking the postern. In a complete front, its properties re-appear, but its relief must allow to the whole flank a sight of the foot of the escarp of the bastions. At present it is no longer revetted except at the wings. The form of the modem system is generally the best, but there is still a dead space along the flanks. (332). Coimterguards or Coiivre-faces are thrown up before the bastions or ravelins, as we have seen in the second and third systems of Vauban. Sometimes they have a narrow torre])lein, and are either scarped with masonry, or are entirely of earth. 7 Faubaii gave a great thickness tu his countcrguards, whilst other engineers — OITWUHK^ 355 Cormontaingne, Bousmard, Caniot, &c.— made them very narrow, to prevent the besie"-ors from availing themsehes of their torreplein, and constructing breaching batteries on it. Experience, however, decidedly jjronounces in favoiu- of Vauban's ideas, who reconnnended not to assault these works, but to destroy their parapets, in order to permit the breaching batteries of the covered way to batter down the enceinte. If the counterguards are employed as a mask to cover the enceinte, a great thickness is certainly desirable, and the besiegers would not save time in assaulting them for the purpose of constructing new batteries in their terreplein. At the siege of Landau, in 1703, Marshal Tallard lost time in assaulting the counterguards, and was thereby obliged to encomiter the Count de Nassau ; and had he not succeeded in beating him at Spii'e, the consequences would have been most disastrous ; whilst the breaches to the enceinte could have been made at once, by merely giving an extra relief of 3 feet to the batteries of the covered way. At Turin, in 1706, La Feuillade made the same mistake, and not only lost the place, but was beaten by Prince Eugene. A similar mistake of carrying successively every enceinte, whilst they could be sinmltaneously breached, was made by Wellington at Burgos in 1812, and he was compelled to retire after five murderous assaults. Counterguai'ds are not so frequently constructed at present as they used to be. Whenever em))loyed, either before a bastion or a i-avelin, they should completely cover the masonry and never hinder the fire of these works, conditions which have not always been fulfilled. They are found in old fortresses chiefly before l)astions, deriving their flank defence from the ravelins or from their reduits. They dinjinish the depth of the re-entering space between the ravelins, so that the enemy can crowTi simultaneously the salients of the ravelins and of the bastion. Their long faces being exposed to ricochet, they are untenable by the defenders, and their ditches as well as those of the ravelins become dead, the covered way is abandoned to its own resources, lor the enceinte can hardly fire over tlie counter- A A 2 35G ADDITIONAL AVORKS. guard, and the combination of command between these works renders the construc- tion of a redoubt of re-entering place of arms veiy difficult. The shoulder angle of the redoubt of ravelin, can be breached through the ditch of the counter- guard, and it may be stormed at the same time as the ravelin. All these incon- veniences, added to the great outlay they occasion, have not a little contributed to throw counterguards into discredit. Nevertheless, when old fortresses, the masonry of which is generally exposed, are repaired, counterguards are found to answer well, as they ai-e cheaper than tlie work required for raising the eounter- scai-p, the covered way, and the glacis. Sometimes they are constructed on a better principle, as in the following disposi- tion called & front of counterguards, where they mutually flank each other, but the Fio. 631. / best disposition would Ije that in which they are flanked l)y the enceinte itself, and this is only possible in certain localities. Several engineers have I'e- commended counterguards in preference to ravelins, but Vauban and Cormon- taingne, decidedly object to them ; however, it must be confessed that in their time, the counterguards in use were very bad, scarcely covering more than half the length of the faces. They have important advantages, inasmucli as the enceinte being protected the enemy must occupy them before breaching the bas- tion, and they detain the enemy longer than ravelins would. On the other hand, they do not give a cross fire on the capital of the bastions, and the enceinte being unable to fire over them, there is not so great a development of fire against the attacks ; it is difficult to flank them, and to organize good retrenchments in them. French engineers seem to prefer them to ravelins, and they form coupures on the terrepleins to defend the salients ; a redoubt of re-entering place of arms is also constructed to fire on the collateral capitals. Both countcrguai-ds and ravelins are seldom used together, except in places of importance. Counterguards have occasionally been placed before i-avelins, especially when these were small. If the ravelins are large, the advantages gained are not a com- pensation for the distant, and therefore inefficient flanking of the glacis, of the salient place of arms, and of the salient of the counterguard itself. oiTTWOKKt;. :ir}l The name of envelope has been given to the continuous enceinte, formed wiicn the countcrguards of the bastions are joined to those of tlio raveUns ; it may increase the length of tlie defence, but coupures must bo made to prevent the enemy from spreading, and a strong armament should be given. To conchide these remaks, wo may add tliat, when counterguards cover the masonry, the ghicis may be gi'eatly simplified. It causes a serious outlay, which can be reduced by giving the minimum conunand to the covered way, the terre- plein of which may bo below the level of the countiy. The glacis, still seen by the enceinte, is thus made very small. (333). Tenaillons and Demi-Tcnaillons are emi)loyed to strengthen tlic small ravelins of the old tracings. I'"l0. 632. Those works by increasing the saliency of the ravelins, had the advantage of compelling the besieger to cany two ravelins before attacking a bastion, but their cost is great comjmred to that of a counterguard, and ^they are no longer con- structed in modern fortifications. (334). Formerly, hormcorks were in high repute, and might be seen in almost even- fortress ; they were sometimes erected to excess, and yet, such as they were, they had but little value. KlO. 633. -A The long branches are exposed to ricochet ; the front, being narrow, is easily enveloped and silenced, and the ditches permit the besieger to breach both bastions. Vauban certainly made an improvement by constructing the hornwork before the bastion, because the enemy is thus compelled to carry the two collateral ravelins, md erect the breaching batteries i n the terroplein of the work itself, and then 1r 35S ADDITIONAL AVORKS. will only be aLle to breach one bastion. On the other hand, the long brandies are still enfiladed, and the ravelins that flank their ditches require to be garrisoned, since the enceinte cannot fire into them. In both cases, the long branches have the gi-eat inconvenience of masking the fire of the collateral works, thereby allowing the enemy to proceed with compai-ative safety into the spacious terreplein. Again, unless the ground be especially favour- able, the command of these works does not permit the men on the bastions to fire over them, and part of the enceinte does not command the country ; they require an increase of gai-rison, an inconvenience which ravelins or other outworks flanked by the enceinte do not entail. And, lastly, they occasion great outlay. They should not, therefore, be indiscriminately employed as they have been, and the addition of coupures, which increase the cost without adding to the value, such as are here represented, should be set aside. In general, and despite all the inconveniences which we have enumerated, a hornwork cannot be replaced by any other work when protection is required for a bastion forming a salient. They are excellent for enclosing suburbs, and forming tetes-de-pont. Their sjjacious terreplein, too, is useful to construct military buildings on. When constructed, the front should, as much as possible, have the same dimension as that of the enceinte : the escarps should be higher than those of ordinary outworks, about 20 feet, although those of the branches may be only orTWOKKS. ;559 15 feet. Ravelins or countorguards may bo added, but this accuiuulation of works will rarely give an increase of strenptli jiroportionate to the outlay. Croiniworks are employed for tlio same purpose as hornworks, and all we have said about these is api)lic-able also to theiji. Hoth recpiire a covered way. Kio. 637. (335). The covered way is an outwork, which can never be dispensed witli, unless the fortification stands in front of an impracticable marsli or on an in- accessible rock. It has been successively improved by Vauban and Cormontaingne, but its essential property — that of enabling the garrison to go the rounds and assemble in safety before and after sorties — must not be overlooked. The con- struction of a banquette to give musketry fire on the glacis, that of a re-entering place of ai-ms to support the defenders in the branches of the covered way, and that of traverses to resist ricochet are excellent improvements, but these should not cause us to overlook the fundamental property. The traverses, for instance, render the communications along the covered way difficult, not to say dangerous ; and nothing has yet been devised to remedy this. The ten-eplein was originall}' on the ground itself, or a little below, so that tlie crest had a small command, quite insufficient to conceal the masonry of the escarp. Cormontaingne was the first engineer to introduce the rule that the crest of the glacis must cover the masonry : the increase of command which it implies occasions very great remblais, and in order to diminish them, 3 feet of the escarp may be left uncovered, since it will not endanger it. At present the covered way is constructed so as to give a command of 8 feet to its crests, covering the masonry, and to allow at least 15 feet command over them to the parapet of the enceinte : these parapets sliould also present a view of the top of the counterscarp, or at least of a point 3 feet above it. The ditch of the ravelin being narrower than that of the enceinte, the connnand of the ravelin over tlie crest of the glacis cannot exceed 5 or 6 feet. Both the covered way of the bastion, and that of the ravelin, should be com- manded iiy the re-entering |ilace> of arms. •MiO ADDITIONAL WORKS. The glacis should ha exposed to a sjrazing fire of musketry from the crest of the covered way, as well as to a musketry or artillery fire, either direct or reverse, of the works in rear. Their prolongation must, tlierefore, pass 3 feet below those crests when armed with artillery, or tlurough the crests themselves when only defended by musketry. Their surface should as much as possible be plain, and salient edges or deep gutters should be carefully avoided. An excellent dis- position, adopted in Germany, consists in planting the glacis with trees : these being cut down diu-ing the first period of the siege furnish timber, whilst the roots form a serious obstacle to the progress of the saps. When the ground sinks in front, it is often advisable to avoid the remblais necessary to complete the glacis, and to terminate it by a slope, forming what is called a " glacis coupi :" this slope should be exposed to flank and reverse fire. In general the inclination of the glacis is -rV 5 but it may vary from -j^ to -fVj and even be steeper, provided it is seen by the defence, inasmuch as the construction of the sap, trench cavaliers, &c., is rendered difficult. The redoubts of places of o?'??i« are usually constructed during the siege, I)ut in important fortresses a ])prmanent organization is preferable. They may bo erected in salients as well as in re-entering places of arms. A loojjlioled wall inin across the terreplein will answer the jmrpose, if nothing better can be done. A solid block-house connected to the counterscarp by a stockade, and preceded by a small ditch, called " diamond " in Germany, is frequently fomid in that counti-y. The best redoubt is formed of a revetted parapet, such as that of the modern system. The redoubt should leave 10 yards of terreplein to the place of arms, and be preceded by a small ditch of 12 to 15 feet, which, how^ever, should not indent the counterscarp so as to leave less than 15 feet of masonry above the bottom of the main or ravelin ditch. Its relief should not mask the fire of the work in rear, and yet it must be such as to afford a sight of the glacis. Many engineers recommend the construction of a loojiholed gallery behind their escarp, from whicli the terreplein of the place of arms may be fired on. ADVANCED WORKS. 361 Tlio redoubt of the re-entering place of arms should derive its defence from the Ijastion and from the redoubt of the ravelin, and at the same time its tcrreplein should be defiladed from the salient of the ravelin itself, otherwise the besieger may turn it. In this respect, the redoubt of the modern system is defective, since it cannot bo defended when the besieger has taken the ravelin. SECTION II.— Advanced Works. (336). Advanced icorks are those placed beyond the glacis, but near enougli to receive protection from the body of the place. They are designed to oblige the enemy to commence operations at a greater distance, to defend certain paiis of ground which cannot be seen from the parajiets of the front, to co\er a bridge, a sluice, or a dum, which it is essential to preserve, and to increase the number of assaults the besieger has to give before attacking the enceinte. They have, however, serious disadvantages : they derive but a weak protection from the place, and ai-e exposed to attacks of vive force ; they require a special garrison, and once occupied by the enemy become advantageous to him for the consti'uction of his trenches. As a rule, they are not constructed for small fortresses, and when employed they should not be further off from the enceinte or the outworks than 400 yards. (337). Lunettes. Modern engineers have proposed to constmct these before all the salients, so as to form a sort of line with intervals, but their ideas have not found favour, because such works ai'e exposed to simultaneous attacks ; they sub- divide the gai-rison, and weaken the energy of the defence. They are now con- structed only on the capital of some bastion, and flanked by the collateral ravelins. 'I'lieir salient angle cannot be more than 60° or 70°, because the faces must be at ri gh t angles ornearly so with those of the ravelins. It is usual to give 60 yards to their faces and 20 yards to their flanks ; these are directed so as to defend 362 ADDITIONAL WORKS. either the salient or the gorge of the next lunette. In order to prevent the enemy from erecting batteries in them, the rampart is but 10 yards wide, and their terre- plein is cut by a ditch with a stockade forming a reduit The crest of the parapet FlQ. 641. should be in the same plane with that of the glacis, or not more than 3 feet above it, otherwise the enemy might plunge in the covered way of the ravelin ; th i.s small command exposes the lunette to be turned in the rear, and to avoid tliis danger the gorge is occupied by a wall 15 feet high, 3 feet thick, and provided with two rows of loopholes. There is no need of a covered way, inasmuch as it would lower the counterscarp, expose the escarp, and facilitate the attack by vive force. The ditch may be 30 or 40 feet wide, the escarp and counterscarp 20 feet high, and the crest of the glacis 6 feet below that of the lunette ; this ditch is excavated in ramp as we have seen in the lines with intervals, to expose it to the fire of the ravelins. Communication is established between the lunette and the place by a galleiy opening in the coimterscarp of the salient of the bastion, and in the reduit of the lunette ; from the reduit to the rampart the defenders communicate by two small moveable bridges. When it is not possible to make such a gallery, a double FlO. 643. ADVANCED WORKS. 363 caponier with traverses must be erected, wliicli is a serious inconvenience, since it forms a sap ready made for the besieger. (338). Lunettes d'Ar^on. In order to bring the lunettes further off the place and diminish tlie defect of their gorge, General D'Ar9on has constructed at Besan^on, Metz, and other places, lunettes which bear his name, and which ai'c supposed to be capable of defending themselves. TWs work has the same dimen- sions as an ordinary lunette, except that the salient angle may be made as open as deemed necessary. The gorge is closed by a loopholed wall 18 feet liigh, and a round tower 15 feet in diameter separated from the teiTeplein by a ditch 12 feet wide. The masonry of this tower is masked by the parapet of the lunette, and the top is covered by 3 feet of earth. Large openings under the cornice give a free egress to the smoke, and serve as machicoulis for the defence of the foot of the tower : the loopholes ai'e 6 feet above gi-ound. A lower story leads to a reverse casemate constructed under the glacis at the salient of the counterscai'p for tlie defence of the ditch. A bomb-proof traverse divides the terreplein of the Imiette into two, protecting it from reverse fire : it is vaulted and opens into the ditch of the tower from whence it receives light; four doors establish communication between it and the two moieties of tlie lunette. The ceiling of tlie gallery leading to the casemate is pierced to receive a moveable staircase leading lo steps ascending to the vault : this opening can lie strongly closed after tlie ittreat of thv ilefenders. S(j4 ADDITIONAL WORKS. The circumference of the tower touches only the line of goi'ge, and the wall is directed towards its centre to receive a little flank defence : circular ramps lead from the ditch of the tower to the terreplein of the lunette, and strong bai-riers prevent the passage of the enemy. A double caponier, well palisaded, connects a door in the tower to the place. The lunette D'Ar9on does not seem likely to stand the attack by vive force : the " reduit of surete," the name given to the tower, and intended b}' D'Ar^on to facilitate offensive returns, would soon be destroyed by vertical fire or even by direct fire aimed at the extremities of the flanks, which ai-e weak points. The loopholes of the reverse casemate may be rendered useless by throwing fascines into the ditch, and as the flanks have no defence, the enemy once in the ditch will escalade them easily and surround the tower, and the defenders will retire to the rear, when the lunette is taken before any use has been made of the reduit. Baron Maurice, a Swiss engineer, has proposed a modification of this construction which the figs. 646, 647, will at onco render intelligible: the top of the tower is destined to receive artillery to fire before the glacis; the ditch and glacis alto- gether enclose the work : at the gorge the ditch is flanked by the tower as well as by a little casemate. A gallery passes from the tower to the place, and serves for the retreat to the defenders. The masoiu-y of the tower is still more exposed to tlie artillery of the enemy ; the coranumication to the rear is safer than the cajwnier, but D'Ar<;on had a gallery in his lunette at Metz, and it is an improvement wiiich ADVANCED WORK> 365 cannot be made on every kind of gi-ound ; the defects of the work remain very nearly the same, and tlie simple hmettes of the form we have described are decidedly preferred by the majority of engineers. (339). A fleche is the name given to a little redan placed at the foot of the glacis of a bastion or a re-entering place of anns : it is a work much inferior to the lunette, and is only erected when there is an advanced ditch to defend ; it communicates with the rear by means of a double caponier. (340). Horn-ioorks are decidedly better than lunettes, because their front flanks itself, and at the distance at which they are erected this front can receive good dimensions, and their branches be directed towards the outworks which will flank thcin best. To occupy a hillock or a little valley in front of the place, they are excellent. Croicn-works answer the same purpose wlicn the ground to bo covered is wider. Tlicir gorge is closed as for lunettes. French engineers fre- quently construct crown-works. (341). An advanced ditch is formed by the prolongation of the glacis. An advanced covered way is a covered way on the exterior of an advanced ditch. Tliis work is never constructed on the whole perimeter of a fortress, because the increase of defence is not worth the immense outlay which it necessitates. It is cmiiloyed only on some particular parts, for instance, to occupy the edge of a steep slope which camiot be seen from the place, or to give safe access beyond an inunda- 366 ADDITIONAL WORKS. tion. The flaiiks should rest on good obstacles. It serves only for the exterior defence of the place by the outposts whilst the enemy is still far oft'. It becomes better when it is supported by advanced lunettes, especially before fronts in straight line. Whenever employed, there should be at least 60 yards of interior glacis, the counterscarp should be revetted, the re-entering places of arms provided with small redoubts, and the crest kept below that of the interior covered way. Communication is established by a caponier between the branches of the covered way of the ravelin and the little redoubts. The lunettes preserve their own communications. SECTION III.— Detached Woeks. (342). Detached works are the works constructed at a distance, more or less great, from a fortress, deriving their defence from themselves and designed to occupy important positions, to render the investment more extensive and therefore more difficult, to defend the approach of the most accessible fronts, and to preserve to the garrison the use of the country even after the beginning of the attacks. They generally consist of isolated forts, often of some importance, as at Lyons and Paris, and of redoubts, lunettes, towers, &c. As the relief must be sufficiently great to prevent escalade, the small extent of the fronts of these forts becomes an obstacle to the condition of self-defence, the ditches being mostly dead. Several means have, therefore, been employed to remedy this, as loopholed scarp walls, machicoulis, galleries of reverse, and bastionets. (343). The loopholed scarp umlk weaken the revetment (374), always leave a dead angle at theii- foot, require many men to sm-vey the ditch, and are only employed when nothing else can be done. The loopholes have no action on the exterior, because they are placed rather too low to be defiladed from the fire of artillery. Towers are almost the only works to which a defence based on loop- holes is applicable. (344). Machicoulis leave no dead angle at the foot of the escarp, and are out of reach of the enemy when he has entered the ditch, but they are expensive and exposed to a plunging fire of ai'tillery, which is all the more dangerous from their masonry being usually weak. They are not better than loopholes, and only applicable to towers and barracks covered from the fire of artillery. (345). The galleries of reverse are better, and both French and Germans have frequently constructed them, but they should only be considered as an accessory means; otherwise, the garrison, already small, is further reduced, and the defence becomes less energetic ; the loopholes may be rendered useless by means of fascines, or the gallery itself may be destroyed, the ditch losing its defence even before the breach is made. UETACIIKI) WORKS. 367 (346). Bastioiiets, or small hastions in masonry, either caseniated or open, and Fig. G.">0. \ rr n n ^ placed at the salients of a work, ai'e still better. When casemated, the masonry sliould 1)0 covered by the glacis. In the open ones, the defenders are more exposed, tor if they do not stand exposed to a plunging fii-e from the counter- scarp, they suffer heavily in a narrow terreplein fi'om vertical fire : on account ot this, open ba.stionets are placed at those salients only which the enemy is not likely to attack. (347). The outline of detached works varies indefinitely, almost every form having been adopted. At Lyons, some forts have the shape of a trapezoid, the large base being towards the place, and this form is preferable to a regular polygon, because the angles exposed to attack are thus rendered more obtuse. The gorge of all those works should be closed, as in advanced lunettes, by a wall of the bastion form and a ditch. The covered way will usually be dispensed with, since the small gai-rison cannot spare many men for its guard, and it will be constructed only to give views on such grounds as cannot be seen from the parapet. The further these works are from the place, the stronger they should be : the height of their escarp must increase, and when the distance is such that their garrison will probably be obliged to sojourn several days, defensive barracks arc built generally near the gorge. When the position occupied is very important, the work becomes a small fortress, which may have ravelins, counterguards, covered way, &c. It is considered necessary to construct reduits in detached forts to prolong their resistance, either by imparting confidence to the gamson, or by actually partici- pating in the defence. According to the importance of the fort, the reduit may be a tower, a defensive barrack, a redoubt with bastionets, &c. (348). We shall have an opportunity of speaking of the detached works constructed in Germany, but we c.'miot leave this subject without alluding to the nature of the works now in course of construction in England, because, though thoy bear some resemblance to the German tracing, their construction is far better, and contains many of the iniprovcmoiits which have been proposed by the 368 ADDITIONAL WORKS advocates of the bastion tracing. Witliout in any way setting aside the bastion tracing, the English engineers entrnstcd with the defence of dockyards, &c., prefer tlie polygonal tracing for detached works, because the size of these works would not permit the construction of properly developed bastions, the interior space would be too limited, and the faces of the bastions could not bend themselves so well to the ground, or bring their fire simultaneously on the direction required. We speak of these works as specimens of detaclied forts, but avoid entering into the discussion of the value of the combination made with them for the defence of the approaches of Portsmouth. If taken in their ensemble, the system may be severely criticised as not answering the pm-pose in view, yet taken singly, these forts ai'e constructed on decidedly superior principles. The figures represent the nature of the works in the neighbourhood of Gosport. DETACHED WORKS. 360 The angles are made obtuse to permit one face to take up the fire of the :ulj:icent one. The ramparts of the faces arc protected from ricochet by traverses, either soHd or hollow, to servo as expense magazines, and those of the Hanks which are more exposed to enfilade by traverses casemated h I'llaxo. The l)arapet does not invariably run parallel to the ditch, whose escai-p and counter- scarp arc traced independently of the rampart whenever desirable. The ditches are flanked by caponiers hidden by the counterscai-p, and so con- structed as not to be exposeil to destruction by any battery erected in the prolongation of the faces. They are for musketry and artilleiy, to permit the Section through Mortar use of canister and grape. At the salient of the ramjiart thei'e is a casemated battery for mortai-s (see Sec. II. Chap. XXIV.) The command of the works is regulated so as to sweep the ground in front, and to allow the consti-uction of bombproof casemates under the rampart of the faces. These casemates form excellent bai'racks for the garrison : they ai-e connected in front by a gallery of communication, which is lighted by vertical shafts pierced through the rampart, which also insure ventilation. The parapet is made 24 feet thick for the faces, and 20 for the flanks. The ditch is narrow, 45 feet, and the escarp, 30 feet high from the bottom to the foot of the exterior slope, is thereby protected from distant fire. A chemin des rondes rmis along the foot of the exterior slope, and has for parapet a loopholed wall 7 feet high, which makes up a total height of 37 feet for the escarp. The top of that wall is 6 feet below the crest of the glacis along the faces, and 3 feet along the flanks. Its fall does not endanger the escarp. The chemin des rondes gives facilities for repaii-ing the parapet, which the enemy may have destroyed, and cannot give a footing to an assaulting party, because it is flanked by galleries at the angles. The re\ etments of escarp and counterscarp are made " en deeharge." The gorge is occupied by a casepated keep, either polygonal or circular, that will enable a comparatively small number of men to defend the work. A circular keep, containing accommodation for 100 men, is now in com-se of erection at Brockliurst Fort. It commands the whole ten-eplein, and sufficiently 370 ADDITIONAL WORKS Fio. 654. D DETACHKD WORKS. .ijl j)rojects to the rear to flank the ditch of the gorge, ami to aflord an artillery tiro ditlifult to silence along the crest of the glacis of the collateral forts. It has two tiers of guns, the upper on the tcrrcplein, the lower in the casemates. These casemates are consti'ueted en di-charge, and their wall towards the front is kept as much as possible below the crest of the parapet of the work, but not so as to prevent the guns from sweeping the terrejilein ; it is thereby less exposed to being broached. As for the crest of the keep, it has a sufficient command over the parai>et of the fort to fire at distant batteries, but not to sweep the glacis. The ditch is flanked either by a musketry caponier, as in this case, or by a counter- scarp gallery, from which a subterranean communication leads to the caponiers of the work. The gorge of the forts is closed by a wall, with a ditch and oomitcrscarp con- necting the keep with the inner extremities of the Hanks : it has an earthen banquette on its rear, and is made sufficiently strong to resist a stray shot that might pass over the parapets. These forts are constructed about a mile apart, and are not connected by lines ; but it has been proposed to close the interval between them by a wall 18 feet feet high concealed in a ditch. < / (349). Citadels are small forts erected in the most inaccessible part of a fortress. They are intended either to serve as a refuge for the garrison, in order to prolong the defence after the place has fallen, to command a place recently conquered, or to occupy the key of the position when the place being weakly garrisoned or badly fortified, it is advisable to let the enemy occupy the town and to defend only the citadel. In the first case it consists of a fort with 4, 5, or 6 fronts sufficiently large to accommodate ^ths of the whole garrison, it is best constructed on the circumference of the place, to be enabled to receive the re-inforcements that may an-ive, but the Fig. 657. 372 ADDITIONAL WORKS. fi-onts on the exterior must be very strong, and those facing the town weaker, otherwise, the enemy will at once besiege the citadel, to avoid a double siege. An open space called esplanade is left between the town and the glacis of the citadel, to prevent the enemy from making his approaches imder cover. The escarp of the place should join that of the citadel so as to leave no 'trouee,' and at the same time, so as not to mask the flanking ; the junction can therefore be made with the salient of a bastion, either by a kind of a batardeau or by a narrow branch. Some- times the citadel may be detached fi-om the enceinte on a commanding point, but the fortifications of the place should not be interrupted, and as regular attacks cannot bo carried between the citadel and the place, this part of the enceinte may consist of a mere gorge. The second case is now of very rare occurrence ; the dungeons and castles of the middle ages were citadels of this kind : the populations often hostile to the garri- son, were kept in obedience by them ; should such a citadel be uecessaiy, it will consist of a regular front placed on the circumference. In the third case, the citadel is the principal work, and requu-es to be made strong in proportion as the place is weak; it may be constructed for open towns, the approaches and interior of which may thus be commanded and rendered unfit for the enemy. Many engineers object to the construction of citadels as being anti-national, useless for the defence and even dangerous. They contend that populations arc now more patriotic than in the past, and will share with the garrison in the defence, whilst the sight of a citadel engenders apprehension among them ; that the garrison will be too crowded in a citadel and too exhausted after a first siege to support a second ; and that the possession of a citadel renders the enemy more exacting towards tlie town. However, the majority of engineers recommend them, because if they are not called into play, they nevertheless act morally and impart great confidence to the garrison. (350). Intrenched Camps before fortresses were proposed by Vauban in 1696. He had found that towns were too confined in space to receive garrisons of any importance, and as it often happened that armies were compelled to seek a mo- mentary refuge against a superior foe without intending to abandon the country entrusted to their defence, he provided for it by constructing mtrenched camps around the places. It was thus tliat ho erected those of Dunkirk, Ath, Namur, and Lauterbm-g. This camp serves as a barrier against invasion, extends the defences of the fortress, allows the besieged to refuse battle without losing ground, offers safe magazines, affords shelter to a defeated army, serves as a place of security for materials, cattle, and forage, and by its great development and resources compels the enemy to attack it regularly. The Marquis de Feuquieres, in his Memuires, gives long rules for the selection, establishment, &c., of intrenched camjis, and mentions those of Utrecht, Brissacli, Liege, Ac. DETACHED WORKS. 373 Tho intronchments which surrounded them were at first continued lines, and it FlO 658. is only at a later period that a positive advantage was derived from these camps, by defending them with detached works which allow the troops to assume, at a moment's notice, the offensive or defensive. In fact, this improvement was most necessary : in liis Memoirs, Frederick the Great, when speaking of the camp of Pii'na, said that if it were difficult to carry it, it was not less difficult for the defenders to leave it, and he preferred making use of lines of redoubts disposed on salient and re-entering angles, a method that had already been adopted by Marshall de Saxe, at Maestricht, in 1748. The camp which Frederic intrenched at Bmizelwitz, contained 40,000 men, it was traced and executed in five days, and the allies could not force it. Fig. 659. A c?. o x. ^ "^u proaches of a port in any other way. (352). The armament of the batteries will soon be altered by the introduction of Armstrong guns, but it is still regulated on the principles proposed in 1852 by a royal committee. At Portsmouth, however, a few 100-poundcrs Aruistrong will be in battery before these pages leave the pi'ess. The 8-inch shell gun, and 32-pounder of 56 cwt., ai-e the best ordnance for general purposes, since they are capable of setting ships on fire. It is ad\'isable to have one-third of the guns of the first kind, and two-thirds of the second. For important points, great roadsteads, &c., 10-inch shell guns and 68-pounders arc recommended. For a shallow beach, the 32-pounder of 50 cwt. For short ranges, light guns and howitzers will be sufficient, whilst the 18-pounders are desirable for the batteries of position connecting forts witli one another or with batteries. Mortars are too uncertain against siiipping to be much used, but for some particular cases, it is desirable to have a few 13 or 10-inch at hand. The batteries should be provided with ammunition to last one day's firing, which is secured in powder magazines situated either in the reduit or under the parapet itself. The ammunition is calculated at the rate of 150 rounds for solid shot guns, and 120 for shell guns, besides a reserve of 100 rounds per gun kept in readiness. The proportion of shot and shells is : — for the former, 90 romid shots, 20 shells, 20 shrapnells, 10 case, and 10 gi-ape; for the latter, 80 shells, 20 shrapnells, 10 grape, and 10 case; but when it is for a 10-inch gun, the proportion is 100 shells, 10 grape, and 10 case. It is also recommended to have hot shot furnaces placed to leeward in all batteries. The guns are mounted on ordinary garrison carriages, and on all kinds of naval carriages. When firing en barbette, the traversing platform rests on racers raised on dwarf walls ; when firing through embrasures or casemates, the racers are on the terreplein, and are traced on arcs, the centres of which are a little in rear of their muzzles. (353). Every one is familiar with the Marlello towers erected, in great numbers, on the southern and western shores of England. They weie adojtted in 1796, 376 ADDITIONAL WORKS. and named from a small tower of Corsica, wliich had succeeded in silencing two men of war. They are of different sizes, carry one, two, three or more guns, and serve either as isolated batteries, or as reduits to unrevetted works, or even as forts. The small Martello is circular, with a diameter of about 30 feet, and a height of at least 24 feet, to resist escalade. The platform is surrounded by a parapet of bricks, and mounts one gun, traversing on a central pivot. The ujiper story is bombproof, to serve as a lodgment to the garrison, and is pierced with loopholes, fire place, &c. The lower story contains the magazine, cistern, &c. The door, 10 or 12 feet above ground, is reached by means of a ladder: the platform and lower story, by means of a trapdoor and steps. The thickness of the walls varies from 6 to 12 feet. The lai'ge Martellos are not circular, but of a tracing that varies with the number of guns they mount. The diagram represents a tower for four guns. COAST BATTERIES. Fio. 662. 377 ^"rfrz v354). The ^o'" /. / ^ / 382 CHAPTER XXII. DETAILS OF PEKMANENT WOEKS. SECTION I.— Defilade. (357). The defilade of permanent works is based on the same principles and executed in the same manner as that of field works, but very few fortresses are found in which the problem is satisfactorily solved. The engineers of the time of Vauban did not attach sufficient importance to this subject Cormontaingne was the first to take it in hand, and it has been necessaiy for modern engineers to correct, as best they could, the defects of existing fortresses ; dangerous heights have been lowered, parapets raised, or terrepleins lowered, or tliese three means employed simultaneously. The theory of defilade originated with the French school of engineers of Mezieres towards 1760. At first the engineers imagined, for the sake of regu- larity, a single plane of site tangent to the commanding ground, and constructed their fortification on it as on horizontal ground. As the enemy does not make his approaches on this plane of site, but on the ground itself, this method could not answer practical purposes. A single plane of site for a place is no longer considered a necessity, far from it ; every fi'ont or part of a front may have a special plane, and the more numerous these planes are, the more readily the forti- fication will bend itself to the ground, and thereby acquire additional strength. The distance fi-om which it is advisable to defilade, is still a matter of discussion, but as 1000 yards is the extreme distance at which the besieger constructs his batteries, most engineers would defilade the enceinte from all commanding ground within it ; this however is not sufficient when the place is exposed to reverse fire, because the enemy, with the actual improvement of artillery, may find it advanta- geous to erect batteries at a distance of 1 500 or even 2000 yai'ds, to fire at reverse on the defenders of the fronts attacked. Ravelins or similar outworks are defiladed from 1000 yards only, because the enemy is not likely to erect special batteries on the rear of the parallel, and as the DEFILAOK. 383 covered way is not in request imtil after the besieger has constructed his second parallel, it requires defilading only from 600 yards. The masonry does not re(iuire defilading beyond 1000 yards. In general, this is the distance from which it is necessary to be covered from musketry fire; arms have been improved, l)ut sight remains the same. The plane of defilade should pass 8 feet ai)ovc the dangerous gromid, within musketry range, and 6 feet above the ground on which the enemy can erect his batteries. If possible, the salient places of arms should bo defiladed from the spot on which trench cavaliers are constructed, the plane passing 9 feet above it. Every work should also be defiladed from those in front, the enemy being supposed to stand 3 feet above their parapets. Defilading by sinking the terreplein is more frequently employed in permanent than in field fortification, although both methods are used. In general, we admit no plane of defilade with a greater slope than i'„. When the faces of a work cannot mutually cover each other without too great a relief, traverses are con- structed to intercept the reverse fire, and cover the men on the banquettes, but they present serious inconveniences in outworks, where they mask the fire of the enceinte, afford more or less shelter to the enemy, hinder the communications or narrow the terreplein. In field fortification, where the relief varies within narrow limits, it is often possible to defilade a work by modifying the outline, and although in permanent fortification the limits of the relief ai-e wider, yet the conditions of the tracing are less easy to depart from. Nevertheless it is often necessary to make alterations in the general outline. The application of fortification to u-regular ground is by no means the least important branch of the science, and we cannot do better than enumerate briefly the fundamental principles. When a fortification is erected, either in horizontal or uneven ground, in front of an isolated height, its general direction should be perpendicular to the line that joins the commanding point to the extremity of the work, in order to obtain a plane of defilade as little inclined as possible. If it is constructed before a range of hills or equal altitudes, it should be parallel to those heights. If the crests of those hills gradually incline and intersect the plain, the fortification may no longer remain parallel, but may converge towards the point of intersection. When the fortification is erected on the side of a hill, in face of a plain, it should remain parallel to the latter, and if it must descend towards it, it should do so as obliquely as possible, the summit being occupied by the salient, and the foot by the re-entering parts, since it is from the foot that the enemy can direct enfilade and slanting fire. If the whole place is situated in a valley, the longest sides or fronts are kept parallel to the hills, and the extreme ones that run across the valley lu ing exjiosed 384 DETAILS OP PERMANENT WORKS. to enfilade and reverse fire, are made as short as possible and defiladed by traverses and parados. When a work has a height in front, it is so much the more easily defiladed as its angle is more open ; under such circumstances the bastions should have as wide a salient angle as possible, and flanks as short as the necessity of the defence will permit : ravelins may be dispensed with or have very little saliency. Whenever the position of a salient is not necessarily determined by other circumstances, it is fixed so as to let the prolongations of the feces fall on low parts and contain between then- angle the dangerous ground. As a general rule, we should avoid the vicinity of commanding heights, and be especially careful not to direct long faces towards them. More particulai-ly still, should we leave aside positions surrounded by hills within range. And lastly, it should be borne in mind that a fortification constructed on a slope fiicing a plain, stands in the same danger as a work erected on a plain and having a hill in front, that the most advantageous position for a work in uneven ground is on a sm-face rising towards the heights, and the most disadvantageous on a surface sinking towards them. Besides these considerations relating to the defilade, which apply to field as well as to permanent works, there are others that concern the ground itself on which the fortification is erected Thus, an irregular surface requiring great deblais and remblais should be avoided ; the salients, bastions, and cavaliers should be placed on the chief elevations, the ditches should occupy the hollows, the glacis should as much as possible coincide with the ground itself, &c. (.358). Fortifications are sometimes erected in mountainous districts to com- mand a road tlu'ough which the enemy is obliged to pass, and in this case the general principles cannot be adhered to. Space will frequently be wanting, fronts will be made smaller ; and as the depth of the ditches must still be suSicient to prevent escalade, casemates, loopholed galleries, &e., may be employed. Some- times earthen parapets will have need to bo entirely replaced by masonry, blind- ages, vaults, &c, to protect the defenders from plunging fire. The fortification becomes similar to that of the ancients. It would be endless to enter into the details of the various cases that may occur in momitainous regions, but as a general rule we may say, that the chief work, fortress or fort, should not be erected on the culminating point, because the enemy might turn it by the paths he finds on the flanks of the mountains. This point is occupied by a tower, a blockhouse, &c , and the chief work stands in the valley towards wliich all the paths that lead across the chain converge. (359). Although it is not our province to enter into details of plan-drawing, yet we may show how the command of works may be determined, by means of profiles, from the conditions that may be given. Let us suppose that it is required to find the command of the bastion over the glacis ; the parapet being intended to COMMUNICATIONS. 385 fire at the foot of the glacis, the shot to pass 4 feet above the crest, and to enable tlic defender to see 2 feet above the counterscarp. •f Let E H represent the line passing through the foot of the glacis, and a point F, situated 4 feet above the crest of the covered way. Take A B = 2 feet, and through B draw a line B G, inchned at J . It is clear that the crest of the parapet must be between the lines F H and B G : if on B G, it will give the maximum com- mand compatible with the data of the problem ; if on F H, the minimum. Through R draw R V at 45° to represent the direction of the exterior slope, and through B di-aw several lines B m, B m', B ot", &c., which may represent various superior slopes : from tho points where these lines cut R V, measure horizontally no=:n' o' = n" o" &c. = 18 feet thickness of parapet, and erect the perpendiculars op, o' p', o" p", &c. The points p, p, p", being joined, we obtain a curve (hyper- bola) on which the crest must be situated, since R n, R n', &c., represent the exterior slopes, and n o, n' o', &c., the superior ones. The intersection of this cunc with B G and F H will give the command maximum and minimum. SECTION II.— Communications. (360). Great importance is now attached to the establishment of good com- munications between the various parts of a front, because the defence may receive a greater impulse when there is free circulation, than when there is danger of being cut off or exposed to view while repairing to the threatened point. The chief conditions they should fulfil wel-e not always observed in old constructions, but now engineers endeavour to obtain them : they should not compromise the safety of the enceinte or of tho works to which they lead ; they should be easy of access to the defenders and yet useless to the enemy ; and they should be covered 386 DETAILS OF PERMANENT WORKS. from the sight of the besieger throughout the whole of the siege ; their egress (when underground) or their surface should be seen from the works in rear, in short, they should not be easy to be cut off by the enemy. These commimications take jjlace, as we have seen, by posterns, stairs, ramps, and caponiers. (.361). Posterns are subterraneous passages and must only be constnicted when indispensable, because they more or less facilitate surprise. If in pursuing the defenders actively the enemy succeeds in entering such passages and occupying them even partially, he is enabled to barricade them ; to fill them with powder and IjIow up the work above : it is a danger to which all subterraneous passages arc subject, hence canals, rivers, sewers, aqueducts, &c., are invariably closed at their ingress and egress by gates, and otherwise made secure. Posterns are generally foimd under the middle of the cm-tain, under tlie tenaille, under the flanks of the redoubt of the ravelin, under each face of the redoubt in the re- entering places of arms, and sometimes under the faces of the cavalier in lieu of the staircases which we have seen romid the traverse in the modern system. As a rule, they should not be inclined at a greater slope than -i, and this is why it is so often necessary to make the great postern under the curtain debouch about 6 feet above the bottom of the ditch, a disposition, however, which jjrevents the enemy from forcing the entrance by attaching a petard. A wooden ramp com- pletes the access in ordinary circumstances, but when there is danger in letting it remain, it is replaced by a moveable light wooden staircase. It has been proposed to let the postern reach the bottom of the ditch whenever the slope allows of it, and to defend its approach by a loopholed guardhouse, but it increases the exjiense and is not always practicable. The_ postern through which artillery passes should be 7 feet wide by 9 feet high, except the great postern, which is usually 12 feet by 9 ; those destined for infantry are 5 wide by 7 feet high. In ancient fortifications, the posterns under the curtain, cavalier, and tenaille, were the only ones thi-ough which gmis could pass, but most modern engineers require that all posterns be made wide enough for artillery, to save time in arming and disarming the outworks, an operation somewhat slow, since the guns and their carriages have to be caiTied from the main ditch to the various terrcpleins by means of gyns. COMMUNICATIONS. 387 Botli entrances of a postern are closed by strong gates opening inside, and a tliird gate " of safety" is frequently erected in the middle of the passage. These gates are made of oak strengthened by iron, and ;u"c besides secured by oaken balks inserted into the masonry of the vaialt. The posterns of the enceinte arc frequently turned to advantage : recesses ai"e cut on both sides of the passage to form powder magazines, wliich besides being bomb-proof are very handy for tlie outworks. In the modem system the posterns which lead to the ditch of the ravelin open into the torreplein of the redoubt, but French engineers object to this ai-rangement : they believe that every work should have its own special communication, and they make these posterns pass under the flanks of tlie redoubt and open into the main ditch. (362). Stairs or pas-de-souris, were exclusively employed in the time of Vauban, to communicate from the ditch with all the outworks: now tliey arc found, either single or double, at the gorges of the salient places of arms, of the redoubts in tlic i-e-entering places of arms, of tlie redoubt of the ravelin, of coupures, and of tenaille. They ai'e a precarious means of communication, for the vertical fire of the enemy destroys their steps, or the frost makes them slippery, and even when not so impaii-ed, they are by no means easy to ascend rapidly. Vauban made them only 3 feet wide, and their slope was nearly 45°. Cormontaingne widened them, and diminished the slope : at present they ai-e 6 or 7 feet wide ; the step is 7 inches high, and the thread 1 1 inches, giving a slope of -, V A thread of 1-1 ihches gives a better slope. These stairs are gi-catly objected to by many engineers who prefer ramps fit for ai'tillery, except at the gorge of the redoubt of a ravelin, which a ramp might expose to be turned. (363). liamps are undoubtedly a more rapid means of communication, but it is yet a matter open to discussion Whether pas de sotiris arc not preferable. The outworks once armed, their artillery need not be moved till it is disabled : and if any can be saved, it will not be of great importance to the defence, whilst ramps road turns nearly at right angles, and jiasses through the faces of the redoubt and of the ravelin under vaulted archways provided with drawbridges over their respective ditches, thus forming a level communication with the covered way, fi-om which a winding cut, opened through the glacis, leads to the countrj'. For farther seciu-ity a small place of arms, called "avancee" is constructed at the point where the road leaves the covered way. There would be great danger in tracing the road in a straight line, because then the enemy might enfilade it, and render gi-eat sorties impossible. The enti-ance to the cm-tain is generally decorated with some architectural structure of simple chai-acter. The passage is 15 feet wide, the gate fi-om 10 to 12 feet, and the vault 15 feet high, dimensions greater than those we find in ancient places. They allow for two paths for foot passengers. In commercial towns, however, two passages, one for egress and another for ingress, arc often coupled together. The height of the vaidt, with a thickness of two yards for its masonry, and the earth above, does not always suit the relief of the curtain, and it becomes necessary to raise the curtain in the middle, or to erect traverses or cavaliers at that point. Where these means are not sufficient, the passage is not vaulted. The fixed bridges over the ditches are sohd structures of wood or masonry, or the piers are made of masonry and the rest of timber, in order that it may be easily cut or destroyed. The bridges are from 18 to 30 feet wide according to their importance. As they, more or less, hinder the flanking of the ditch, the arches are made as wide as possible, and when the passage is not much above the bottom of the ditch, a causeway is caiTied from the tenaille to the redoubt of the ravelin with two glacis well defended by the flanks: a coupm-e of 12 or 15 feet is made near the counterscarp. (368). In order to interrupt or re-establish suddenly the communication, draw- bridges arc employed, which consist of two parts, the platform and its counterpoise. 390 DETAILS OF PERMANENT WORKS. The platform, about 12 or 14 feet long, is a stout fr-ame of timber, the liead and tail piece of which are connected by balks. Over these one or two rows of chesses are placed, and to prevent the wheels of can-iages from weai-ing away their surface too rapidly, small iron bars arc closely set over them on both sides. The tail piece bears two iron pins driven right and left into the scarp wall, which wall is made thicker under this part, to prevent accidents, and above it a recess is cut to receive the platform when the communication is interrupted. The head is secured to the fixed bridge by two bolts, and hand-rails are placed on both sides. This structure has a great weight, and requires a counterpoise in order to move it, besides other means designed to surmount inertia and friction ; hence the invention of several systems, but we shall only say a word on the chief ones. In the most ancient, the counterpoise is formed by a stout wooden frame, heavier than the platform, terminated by two long beams called " fleches," which are strongly connected and protrude outside. They bear pivots fixed in the wall, ■\\hilst their extremities are secured to the head piece of the platform by a chain. The part of the counterpoise or bascule in rear of the pivots, must have sufficient weight to balance the platform. The length of the beams, from the pivot to their COMMUNICATIONS. .Hi)! head, is equal to that of the platform, and tlie distance between tlie pivots of the counterpoiso and tlio pins of tlio tail piece must bo equal to the length of the chain connecting the fleche to the head piece. To work this bridge, the bolts tliat secure it to the fixed bridge are opened, the bascule is pulled downwards by a service chain, and the flechcs turning on their pivots raise the platform. Two vertical grooves are cut into the masonry to receive the fleches. The inconve- nience of tliis system is the danger to which the long fleches, seen at a distimce by the enemy, expose the bridge ; the eflorts made to raise the platform are not constant during the working ; the equilibrium is soon destroyed by the warping of the beams, and the timber of the fleches requires frequent repairs. / (369). To avoid the inconvenience of exposure to ^-iew, the bascule has been fixed below, and received into a well hole when the platform rises. This plan is riu. D/o more common in Germany than in France. The scarp wall requires a great thickness ; when the ditch becomes wot, the well-hole is liable to be filled with water, and the counterpoise aequii'ing buoyancy no longer balances the platform. Sometimes a system of cogwheels is employed to lower or raise this bascule. (370). In a system due to Dobenheini, the effort necessary to work the bridge varies with the resistance which the mass presents in the different positions it may take. The platform is Imlanced on the right and left side by two iron bars, one horizontal, the other inclined at 45°, both carrying a weight at their extremity. Each bar is moveable separately j;ound an axis A, whilst the weights are connected by a chain which passes over a pulley B, and is attached to the head piece. By pulling the weight W, the platform is raised, both weights acting simultaneously until an arc of 45° has been described, whcn./c' falls on the vertical, and ceases to 392 DETAILS OP PERMANENT WORKS. Fig. 679. ^'Jil^ act, w raising the platform. The mechanism is simple, but it does not exert a constant power. (371). In the system of Belidor, the comiterpoise formed of iron cylinders, roll on each side on a curve called sinusoid, which is proved m mechanics to possess the property of diminishing the weight of the counterpoise in the same proportion as the platform loses its own when being raised. The curves are made of masonry and bear a rail of iron, on wliich the cylinder rolls. In practice, tlio friction renders the working difficidt, and this jilan requires also much space in rear. (372). In the roller bridge of M. Lesueur of Jersey, the platform and counter- poise belong to the same frame-work, made of oak beams strengthened with iron COMMUNICATIONS. 393 rails. Under it is a rack, bolted to some iron bearers which connect the whole frame. The counterpoise rests on the edge of the escarp, on a roller, whilst at the rear it is provided with a truck and friction-rollers. By means of a pinion and cogwheel, the platform, or rather the bridge, is moved inside the place ; the handrails themselves following and passing on rollers moiuited on standards. The working is not exposed to danger, but it is slow and requires much space in rear ; and means must bo provided to close the opening. (373). The last sort which we shall notice, due to General Poncelet, is fre- quently employed in France, where engineers seem to attach as great an import- ance to constancy of the power, as to secm-ity of workuig. Here the counterpoise consists on each side of a massive iron chain, attached at one end to a fixed point c, and at the other to the small chain that draws the bridge. The great chain is made, as the diagram shows, on the same principle as that of a watch ; it cannot touch the wall, because of the small cham rolling on a pulley, P passes afterwards over a wheel Q that keeps it off. The counterpoise set 394 DETAILS OF PERMANENT WORKS. into motion by one man, descends into a small well. When the platform is hori- zontal, the chain being on ABC, the part B C is supported by the fixed point C, and it is the weight A B that balances the bridge. When the platform is raised to M N', a portion of the chain A A' equal to the difference P N — P N' descends, and the part that balances the bridge is A' B' alone, which is evidently smaller tlian A B, since B B' is only half of A A', in a third position a smaller part A" B" balances and so on, the counterpoise becoming smaller and smaller as the bridge loses more and more of its weight. The pi'oper weight of the chain is fixed after a few trials, and as it is armed with hooks to receive additional weights, the matter is easily settled. It is an excellent drawbridge, the working is easy and simple, it takes very little room, is not exposed, and has only the defect of beuig more expensive than those of the old system. When railways pass across a place, it is not possible to give them tlic same curvature as the ordinaiy I'oads, hence a danger which it is necessary to diminish by the addition of advanced works. These works should be kept at the same level as the covered way, be ti-aced perpendicularly to the front, and be seen along all its surface from the pai-apets. When railways pass under vaults, they should be defended by loopholed galleries. During a siege, all the bridges are removed, the gates or openmgs through the escarps are closed by means of remblais, and the inhabitants communicate with the country through the posterns, those gates only being preserved ou the fronts not attacked, through which sorties can be made in force. SECTION III.— Loopholes. (374). Loopholes are of two kinds, horizontal and vertical, the former of which is rarely employed except for the defence of a ditch in tlic galleries of reverse and caponiers, where a wide horizontal range is required. In vertical loopholes the exterior opening is 3 inches wide, and the interior opening 2 feet. The height must be such as to pennit the men to fire easily in all the directions where fire is necessary, and varies from 1 foot 6 inches to 2 feet. The cheeks with these dimensions are inclined at 30°. The " plongee " \aries with the requirements of the defence, and in mountainous districts it may even counterslope. t LOOPHOLES. Fio. 686. 395 \ \ i/ J/ Sometimes the wide openiii<;- is maclo outside, and the cheeks are indented, thereby aftbrding the same security as in the other arrangement: it presents a better view of the external object, and it may bo adopted for caponiers and galleries of reverse, where the enemy has something else to do than to return fire. When the wall is more than 3 feet thick, the muzzle of the musket cannot protrude outside, and the smoke would become inconvenient : in this case, a recess is cut in rear, or the loop may be made wider both ways. In this case, the exterior cheeks are indented to prevent the bullets of the enemy from ricocheting and passing through. Fig. 687. ^'iG. 688. f Wlien a loop is pierced near the angle formed by two walls, it is necessary to allow 1 foot 6 inches between the wall and the cheek, otherwise the defender could not make use of the whole range. The exterior opening must be kept 7 or 8 feet above the ground outside to prevent the enemy from masking it or firing into it. When, however, the plongue needs to be much inclined to fulfil some condition of defence, the men cannot easily incline tlieir niuskete along its slope, hence the necessity of piercing the loophole down to tlie foot of the wall itself may occm-. Such loopholes su-e called liy the Fi-ench " crencaux de pied." A plongee much inclined is usually indented like the cheeks. 396 DETAILS OP PERMANEXT WORKS. The interior opening must permit the men to fire easily in every direction, and is therefore kept at 3 or 4 feet above the banquette. The centres of loopholes are usually kept 3 feet apart, not to weaken the wall too much. The superior face (top) may be horizontal, but it is inclined when it becomes necessary to limit the vertical range, as in loops pierced through flanks that 1 J face each other, or as occurs in mountainous regions : this inclination prevents the men from firing at each otiier. Loopholes are generally cut perpendicularly to the wall, unless they have to flank a face oblique to that in wliich they are pierced, or when several of them have to defend the same point. I Loopholes may be double when it is necessary to fire in two directions, but they weaken the wall. Horizontal loops are similarly constructed, and what has been said before applies to them ; their opening may be wider outside or inside, their cheeks may be indented, &c. ; the only difference is, that they may serve for two or even three men. Colonel Ord proposed this loophole for two men : it has on each face a break or return to arrest the bullets. LOOPHOLES. Loopholes cover the defenders from tlie musketry of the besiegers, but each man behind his narrow opening cannot see a hirge space in front, and is often unable to fire on the enemy when he presents himself only for a very short time before the range of his loop, especially when close. Loopholes should not be exposed to the view of artillery, hence they should bo used sparingly, as auxiliary means to defend a bridge, or a ditch when the defence from the parapets is not efficient. In Algiers, where the Arabs have no ai'tillery, the French have constructed places, the enceinte of which consists merely of a loopholed wall of the bastion trace. In Germany, loopholes foi'm an important item of the defence, and we shall have an opportunity of judging of their value when speaking of the polygonal fortification. (375). A revolving loophole, that may be advantageously adapted to doors, and at the same time made to serve as a ventilator, has been lately ti-ied at ( 'liatliam, and found to answer well. It consists of a solid cylinder of metal A, 398 DETAILS OF PERMANENT WORKS. that revolves in a casing B, also made of metal. The cylinder is pierced with a hole 2i by 1 ^ inches, allowing an elevation of 14o, and a depression of 19 ',o. Aj)crtures through the casuig permit a horizontal field of 75i°. The cylinder is adjusted to the object to be fired at, by means of the bai-rel acting as lever. To close the opening, the cylinder is turned by means of a handle C, then raised over a cheek o, and kept closed by the handle fitting into the notch to. (376). Embrasures for guns are loopholes on a larger scale. The question is not yet settled as to what is the best form to give them, and yet, owing to the multiplicity of casematcd works, caponiers, coast batteries, &c., lately constructed, it requires a speed}' solution. The two great points to bear iu mind in the construction of embrasui-es are to cover the gunners, and to obtain a wide field. In the old model, the tlu-oat was 2 feet 2 inches wide, whilst the outside opening was made equal to 2 feet 2 inches, inercastd by one third the thickness of the wall. The gun can only traverse 27 degrees, and the outside opening is con- siderable : projectiles striking the cheeks enter the battery, and the acute angles of the masonry at the tiiroats are liable to be broken in. There would be less danger for the gimners if the embrasure were reversed, but the thickness of masonry near the external opening would be too small. Th form has been modified in recent construction thus : — Wtm but if some advantage is thus gained for lateral range, tlie external ojiening is increased. I( was with a view to avoid acute angles at tlic throat tliat the LOOPHOLES. 399 Americans adopted tlio embrasure of General Tottcii, in which tlie tliroat is at 2 feet from the face of the wall, the exterior ojiening 4 feet, tlie interior one 5 feet, and the external height of the cheeks 2 feet 6 inches, the throat itself Fio. 099. being 1 foot 10 inches wide. In tlio con.striiction of coast batteries, American engineers have kept in view the great danger to which tlie gunners are exposed when ships can approach sufficiently near- to use canister, the balls being " carried in " in large proportions ; and to remedy this defect they have adopted an embrasm-e into which the projectiles can only enter through a small opening, the width of the throat itself. But in their new embrasure the masonry is weak at the throat, and liable to be destroyed by heavy ordnance, so much so that they have to strengthen it by wrought iron slabs. Experiments arc still going on, and it is thought that we shall soon possess embrasures coated with iron, really shot proof. To prevent small shots entering tlie embrasure, iron mantlets or shutters are advantageously emj)loyed: thej- are kept closed whilst the men arc loading the gun. (377). Machicoulis. — We have already spoken of the use of machicoulis (344), and we now give an application' of loopholes and machicoulis, as proposed by General Dufour, for a tower of 24 feet radius, destined to be defended by a garrison of 40 or 50 men. This arrangement is advantageous in mountainous districts ("3.58). 400 DETAILS OF PERMANENT WORKS. Fio. 703. n^ SECTION IV.-Casemates. (378). Casemates, or vaults destined to protect troops against vertical fire, and constructed under the ramparts or elsewhere, form an excellent addition to all fortification ; but opinion is divided on casemates for guns mtended to perform an important part in the defence. They have found strong advocates since the discoveiy of ricochet and the employment of vertical fire, and it is argued in their behalf that both gunners and guns are safe against such fire, and that by placing casemate above casemate the defence may acquire a great superiority of fire over the attack. But if a casemate commands a view of the approaches, it is exposed to direct fire, the wail is easily bi-cached, and the shot that enters through the embrasure causes much harm : besides, the smoke is always more or less troublesome. Whatever be the system of ventilation adopted, it will happen in still weather, as is often found in the ditches of a fortress, that the smoke will remain many minutes outside, Ijcfbrc the mouth of the embrasiux'. The casemate loophoi.es. 401 is almost in tlie dark, nothing can be seen, and the precision of fire cannot be relied upon. Therefore, of two batteries of equal force, one on the ground, the other casemated, the latter will be under a disadvantage. As for the superiority of fire, it is a doubtful question, for it would imply an immense expense to construct stories of casemates on every front exposed to attack, as well as an immense ai-mamcnt; and oven then, the besieger, instead of superposing his guns in one battery, could extend them horizontally, thcreljy presenting a more uncertain aim, and often avoiding the range of the embrasures, whilst every one of his shots would tell on the stories of the casemates. The great armament of the defence will only necessitate more powerful battering trains than have been liitherto employed. As accessory means, however, casemates are excellent. They should be 15 feet wide and 15 long when open on the rear, or 20 when closed : the height of the vaults should vary from 9 to 15 feet The piers of the vaults are 3 feet thick, and are pierced with lateral openings to give room to the men and facilitate the circulation of air; and vents. or chimneys should be so contrived as to permit the smoke to escape freely. The embrasures have the shape of loopholes, and the genouillere should be made as high as possible to jjrotect the men from any shots that may enter through the embrasm-e. (379). General Haxo, a French officer, has proposed casemates that bear his name : they have been constructed at Grenoble and other fortresses. They consist of a vaidt thrown over the gun situated on the terreplein of a work, but not over its embrasm-c. It is open at tlie rear, and acts as a 'traverse. The cheeks of the embrasure are revetted with fascines. The fire is thus less plunging than from guns in bai'bettes, the smoke circulates freely, the masonry is not exposed, but the merlons do not present a great resistance. They are 12 feet wide by 18 long, and 9 feet high ; and above the genouillere they are only 6 feet high. These dimensions are too small, and as the genouillere can only be 3 feet high at the utmost, the gunners are exposed. D D 402 DETAILS OF PERMANENT WORKS. Fio. 706^ IC e represents the top of the escai-p, ec the exterior slope, and ch part of the superior slope of the parapet, the casemate is contained by tlie wall b m buried in the parapet] and the wall p q which is pierced with a large hole for the passage of the smoke. A slope of earth c b covers the masonry. On the roof of the casemate stands the new parapet bap, which may serve for a second tier of guns. Wells pqrs pierced through the terreplcin connect the several casemates of a battery, and give issue to the smoke. The advantages possessed by these casemates are great: they take u]) but little space on the terreplein, which remains sufficiently large or requii'cs but little remblai to afford room for a second tier ; their embrasures may be marked by sods, so that they may be concealed till the moment they are called into play, and the garrison finds bombproof covers. The earthen embrasures do not, however, allow so wide a range as those of ordmary casemates. The wall in the fi.-ont is still liable to be destroyed by direct fire, and this defect it is attempted to remedy by coating the exposed part with iron. Until these attempts prove successful, it is prudent to construct these casemates on the pai-ts of the rampart which are not likely to be exposed to direct fire. The vault lowering towards the front impedes the gunners ; to avoid this, in recent con- structions, it has been made of uniform height. The rear wall is also suppressed. TIio annexed figure represents a casemate for two gims as executed at Gosj)ort. POWDEU MACiAZINES. 403 (379 a). Poicder magazines are found in every fortress. Those containing enough of mado-up ammunition to last 24 hours, or expense magazines, are tempo- rary bomb-pi'oof constructions situated in the works themselves ; there is usually one per bastion. The large or principal magazines are erected as far as possiljle from the fronts exposed to attack. These are strong buildings of variable form. The magazin of Vauban, containing 100,000 pounds of powder in tiers of three barrels, is an arched building 60 feet long, 25, feet wide, and 18 feet high inside. D u 2 404 DETAILS OF rKHMANFA-T WORKS. Kio 711. '■'"' Tlie side walls are 8 feet thick, are strengthened by counterforts, the end walls are 4 feet thick, and the minimum thickness of the arch 3 feet. To prevent the powder from getting damp, some air holes are pierced through the walls so as to cause ventilation, and their peculiar form prevents anything being introduced through the opening, which is furthermore covered inside with a copper net, iron beinc entirely proscribed. Sometimes the building is formed of three or more arches. The following diagram represents a powder magazine at Lille, containing 1 raiSlJLZQ N J 150,000 lbs. of powder. It is surrounded by a wall which masks the entrance. The counterforts of Vauban are objected to on account of their shadow, which causes the wall to keep moisture in the corners, and the form of these buttresses is an improvement, although many engineers would prcfrr to sec the counterforts ■U).') constructed inside the walls. The arch is protected by 3 feet of earth, and the roof is made of sheets of lead. As there must always be much lead kept in store in fortresses for the casting of bullets, the metal may as well be kept in sheets, and thus serve for roofing, thereby saving the cost of i-epairs entailed by oi-dinary roofs. SECTION v.— Water. (380). The presence of water, despite its inconvenience in some resi>ects, is nevertlieless advantageous to the defence, and often renders it possible to simjilify the fortification. Wjicn, for instance, water is found 2 or 3 feet below the surface of the ground, it is hardly possible for the enemy to construct his approaches, and tlie fronts, no longer liable to attack, may consist of an unrevetted enceinte with a long curtain and small bastions, a wide wet ditch with at least 6 feet of water, and a covei'ed way. If water is found at a greater depth, at 6 or 10 feet, the principles of Coeliorn (296) may bo applied. The enceinte consists of a small front; the escarps are revetted, and 18 or 20 feet high, the ditch is 20 yards wide, and its bottom is kept just above the level of the water, so that the enemy cannot sap through it. Before it, stands a second enceinte formed of unrevetted comiterguards and a tenaille similar to those of Vauban, preceded by a wet ditch about 40 yards wide. The ravelin is similarly organised, having a revetted scarp, a dry ditch, an um-evetted counterguard, and a wide wet ditch. A low covered way surrounds the whole, but its re-entering angles are not sufBciently deep to receive redoubts. But when water is 12 or 15 feet below the ground, the principles of the tracing need not be modified, the relief alone alters and becomes less, since the flanks need only preserve a view of the surface of the water. The ditch 18 or 21 feet deep, has an escarp raised 18 feet above water. Although it is preferable that the masonry should be carried to the bottom of the ditch, yet reasons of economy sometimes require this 1 8 feet scarp to be erected on a berm 6 or 9 feet wide left on a level with the surface of the water, but this can only be done in good silicious or calcareous soil. The tenaille needs no revetment except on the wings. The out- works are constructed either with dry or wet ditches. If their ditch is dry, the construction requires no alteration, but if it is wet, the ravelin may be left altogether unrevetted and its ditch widened. The redoubt is still revetted with its cb-y ditch, but is necessarily smaller on account of the space occupied by the earthern slopes of the ravelin.* At last the glacis, on account of the reduction of command, must not be more than 6 feet above ground, because it would otlier- wise necessitate great remblais to throw up its glacis. The communications across wet ditches may lie curried bv means of light bridges 406 DETAILS OP PERMANENT WORKS. as already explained (152), or by boats. In some French places however, they ai-e organised as follows. The great postern opens on a level with the water, and a boat placed Icngthwaj's leads to the tenaillc. To this work is attached a double caponier, the glacis of which are replaced by pai-apets ; it extends to within ten yards of the gorge of the redoubt of the ravelin, and is at this extremity capped with two oblique traverses that limit the passage inside to 3 yards. The obliquity of these traverses enables the enceinte to flank the coupurc of 10 yards that sepa- rate the caponier from the redoubt. Occasionally this caponier is replaced by a canal with defensive banquettes. A small bridge or a boat leads from the capo- nier to the redoubt of ravelin. When the ditch of the redoubt is dry, the usual posterns and ramps arc employed, but when it is wet, a berra 9 feet wide, follows at a level with the water the profile of the redoubt, and the gorge of the ravelin, where a coupure of 8 yards is again crossed by means of a boat, and is produced as far as the gorge of the redoubt of re-entering place of arms. The three coupures between the curtain and tcnaille, between caponier and redoubt, and along the gorge of the ravelin, are deemed sufScient for security, but this system can scarcely be called an improvement on the old method. (382). Inundations secure against attack the fronts they smround, and permit a more vigorous defence to be made on the others ; they protect the neighboiu-ing bastions from enfilade, and when they extend both above and below the place they hinder the investment, interrupt the communications of the enemy, and oblige him to construct bridges. When they are extensive, some lunette or redoubt erected some 60 or 80 yards from the shore, will often render the advance of the enemy impossible, or if the salients of the trace are protected by them, the enemy is compelled to attack the long intsrmetliary sides as at Strasbourg. Their expense is not great when compared with the advantages they insure to the defence, and their only disadvantage is the unhealthy condition in which the garrison is placed by pools of stagnant water. In marshy and low comitries, natural mundations are sometimes produced by lakes and ponds, but the depth is rai'ely sufficient to afford security. The most favorable condition is when a river traverses a place erected in a valley, the sides of which have only a small inclination, more especially when the fall of the bed is not great. The dispositions most generally adopted are as follows : —The coiu'se of the stream is intercepted at its entrance into the place by a sluiced dam or barrage, or what is better, by two of them in case the enemy should destroy one. The first constructed on the counterscai'p A, is called sluice of " retenue" or of "prise d'eau," the second made luider the ranijiart, or fiu-ther in, if necessary, is called sluice of "surete." By closing sluice A, the water rises on the bed, overflows and forms an inuiulation above the place. This inundation is maintained at a proper depth ])y dams defended by advanced lunettes. If when the sluice A is open, B were also opened, water would enter the ditches, but it is not permanently allowed, because the mud deposited, would in time, raise the bottom. Batardeaux D, C, above, and D', C, below, prevent the water from entering. Inundations below the place are also advantageous, although they are more exposed to destruction by the enemy ; they are maintained by dams across the valley, and fed by the inunda- tion above, either through aqueducts or waste-weirs. Auxiliary dams may besides be thi'own up, both above and below, to cover a greater surface of ground, but thev require works for their protection. In some cases the inundation above the place may serve to flood the valley below on a sudden, by merely opening the sluices of " retenue" and of " surete." Besides the protection due to these inundations, the dispositions of wliicli vary \\ ilh every place, water provides active means of defence for the ditclics. 408 DETAILS OF PERMANENl' WOEKS. The batardeaux D and C, are provided with shiiccs called flood gates, and those D', C, witli sluices named sluices of " fuite," which permit the garrison to fill and empty the ditches at will. When a place is threatened with a siege, an inundation is etteeted, and the ditches are kept full till the latter part of the investment ; but when the enemy has begun his approaches the water is let otf to facilitate the communications and the sorties. When the besieger has fairly advanced, his passage across the ditch, the flood gates are opened and his work is destroyed by the impetus, and weight of the water; the sluices of fiiitemay then be employed to empty the ditch for the purpose of repeating the manoeuvre called " chasse" by the French ; or tlie ditch is kept full. The besieger having made a fresh descent and constructed a bridge across the ditch, the water is let ofl" through the sluice of fuite, and tlirough the flood gates too, when an impetus is required, and the ditch is again cleared. By these or similar measures the defence may be protracted. When the volume of water is not considerable, intermediary sluices forming a sort of locks in the ditches may be constructed, so as to give chasses without draining the inundation. (383). The baiTage, as we said, is made either under the aixhes of a bridge in the town or under the rampart. The most simple consists of sliding beams which are let down one by one into vertical grooves cut into the piers ; two pairs of grooves in front and two in rear of the arch are usually cut, and the interval ^3 between the two barrages may be filled with earth. Every beam has a ring near each of its ends, so that by means of a hook, it may be removed or let down to keep the water at the requisite level. Sometimes the grooves receive a gate which is raised by a crab or by winches, but the pressure of the water renders the working difficult. Another sort of bai-rage is made with vertical beams ; a strong wooden structure, a bridge for instance, is run across the bed or between the arches of a stone bridge. The beams are thrust into the river one by one at an angle, as shown in the diagram, the stream acting on them brings them to the vertical, and their lower extremities rest on a sill made either of wood or of masonry. WATEK. Fio. 717. i!a Tlirougli the batardeaux water passes by means of vanes sliding up and do\\ni in a projection of masonry, built at the foot of the wall ; it is worked by a crab, to which access is given by means of a narrow wooden bridge supported by iron ^B ^^ ^^ hooks. This is easily destroyed l)y the eiieuiy, and it is better to make the wall strontier and to construct a vaulted passage through it leading to the work of the vane. DETAILS OF PERMANENT WORKS. Fio. 720. Sucli small sluices, however, do not give passage to a great mass of water at a time, and turning-gates are preferable for the " chasses." A gate A B turns round a pivot C, nearly but not exactly in the middle, so that the pressure on B C tlic greater side keeps it shut. A small vane d d cut through B C, may be raised either by hand or by a crab, and the surface jiressod by the water becomes greater on A C than B C, and the gate is thromi ojicn when it is kept fixed to the huilers h h. To close it, the vane is let down, a little impulse is given to the gate, and the pressure of the stream soon shuts it. These gates easily get out of order. Dams vary much in nature, and are made either of earth as in the field, or of masonry. When they are required to maintain the inmidation at a constant level, waste-weirs are prepared on the whole or part of their lengths. The down side is made either at a small angle or of two arcs of a circle, to prevent the furmation Fig. 722. Fio. 723. of pits or the occurrence of accidents which might injure the work. Sometimes the dam consists of a vertical wall, and tlie water iinis over an inclined plongce forming sally, and as the depth below should be ccpial to the height of the fall, a small ditch or hollow must be excavated. In some localities the weirs are like those which wi! have spoken of in Field Fortification. SECTION VI.— Details. (384). Tho execution of permanent works differs from tliat of field-works : it requires a long time to construct a fortress, and costs the State no small outlay, it is therefore important that the project and estimates should be carefully studied beforehand. It is a long and tedious task, and one which exclusively belongs to the province of the military engineer, so that we shall only say a few words on it The ground is represented on paper, at a proper scale, with the horizontal contours, the tracing is made on that plan. Every part of the fronts is discussed : the organization of the mines and of the water defences is prepared ; the reliefs and the commands ai-e also determined, and it is only after many attempts and trials that tho plan can be satisfactorily settled. But this is not all, the dcblais uuist balance the rembluis. Both are valued approximatively by the prismatic or the centrobarique method, neglecting the foisonnoment, since there is no incon- venience in making the parapets a little higher than they should be, if the earth has time to sink and settle. It is necessary that each part of a front, and if possible each face, should be constructed of the earth immediately before it, as the transport of earth from a distance occasions a loss of time and an increase of outlay. It is therefore after many trials that a satisfactory solution of the problem wmII be arrived at. The plan or project being so far settled, the next step is the calculation of the the expenditure for the excavation, the transport of earth, the construction of masonry, parapets, &c., &c., so as to pi'csent an estimate of the total cost of the fortress. It is only when this estimate is completed that the Government can discuss the propriety of executing the work. With regard to the tracing on the ground, it is done by methods similar to those resorted to in the field, but with more accuracy. Before concluding, we may add that in every country special laws preveut the inhabitants of a fortified town from ei'ecting buildings that would hinder free circulation at the foot of the ramparts, or obstruct the space uecessai-y for the defence and the communication. These laws also prohibit building, excavatuig, or planting outside tlie place, at such a proximity to the fortification as would aflbrd cover to the enemy during a siege. The roads, canals, railways, &c., pass- ing through fortifications are liable to certain restrictions, and these matters arc usually settled by a conunission consisting of militai'y and civil engineers. (.384a). In order to compare tho relative values of fortresses, Cormontaingne oniployt.'d a iiK'thod known as tho " scale of vo'inparisoii." It consists in att;icking 412 PEKMANENT WORKS. on paper, without taking accidents into account, the fronts to be compared : the besieger is supposed to carry on liis approaches according to general rules, as he would before a garrison determined to defend itself, and to employ for each con- stnictiou of batteries, trenches, &c., the average time which the experience of past sieges has given us ; the garrison, on the other hand, is supposed to do nothing besides the ordinary fighting, and to make no sorties, mines, counter-approaches, coupures, retrenchments, &c. The duration of the defence forms the scale. General Fourcroy* attempted to iinpi'ove this method, but he fell into a great error : he compared places by their moments, namely the quotient of the number of days of defence by the cost of one front. Those days which he admits into his calculations as having the same value, it is in reality almost impossible to com- pare : the advance made and the loss suffered in a day of the first parallel, being widely different from those of the twenty-four hours employed in crowning the glacis or forming a lodgment on a breach. The method of Cormontaingne may be employed advantageously : of two fronts costing the same, the better will bo that which is capable of a longer defence ; the less a front costs and the longer a defence it is capable of, the better it will be. But it should be understood that this method gives only an appi'oximative idea, and that the duration of the defence is a minimum. Two very important items, viz., the energy and talent of the governor and the enthusiasm of the garrison and population, ai-e overlooked. This calculation of tlie probable duration of the defence for forti'esses of dif- ferent systems on various polygons, has had this inconvenience, that governors of places became imbued with the notion that they were not bound in honour to defend themselves beyond that time, so much so, that Napoleon complained of it when in 1809 he requested Carnot to write, " on the defence of fortresses." * Fourcroy (Charles Ren^ de Ramecourt), born 1715, died 1791, was a General in the French Engineers, and a contemporary of Cormontaingne. 413 CHAPTER XXIII. PRINCIPAL BASTION SYSTEMS. (385). Bousmard (484), in 1797, published a system which possesses remark- able features. Having traced the enceinte of Vauban's first system, he divides the crest B C of the flank into eight equal parts, and the original face into the same number, being respectively 6, 8, 10, 12, 14, 16, 18, and nearly 20 yards in length. The new faces will be composed of eight broken lines, obtained as follows: through the first division of the flank, and the opposite shoulder angle, draw a line and produce it as far as m, where it is met by the perpendicular drawn upon its direction from the first division of the face ; through the second division of the flank and that extroiuity m, draw a line, which will likewise be limited in n by a perpendicular dropped on It from the second division of the face; through the third division of the flank and n, draw a line, limited by the perpendicular dropped from the third division of the face, and so on. The flanks are also traced on a curve obtained bv drawiuij from the ane which enables tlie NOIZKT. 419 bastion to see the whole ditch of ravelin. Before the mask, and separated by a small ditch, is a caponier of earth forming a covered way and glacis. The masonry of the bastion is thus well protected. The shoulder angles are covered by traverses constracted at the extremities of the tenaille. The covered way is of the same nature, but the tracing of the traverses and their crochets is complicated by geometrical constructions. The connnand differs little from Cormontaingue's. Noizct gives an increase to the salients in order to protect the faces against ricochet. All these modifications are decidedly improvements ; the enceinte powerfully flanks the outworks, and the communications arc safe; but as the alterations bear merely on points of detail, it is doubtful whether they would seriously increase the dm'ation of a siege. (388). Dufour's system (488). The enceinte is traced as in the modern system ; the ditch is 30 yards wide at the salient of the bastion, and the counterscarp is directed on the shoulder angle. The ravelin is considerably altered by the erection of a cavalier or bonnet, 24 feet high, at its salient. This mass is destined to protect the artillery of the ravelin 420 PRTNCIl'AI. BASTION SYSTEMS. against ricochet fire, and General Diifbur calculates that, by giving to the faces of ravelin a slope of 3 feet in their length, the terropleius will be perfectly secure from ricochet for a length of 270 feet. To trace this outwork, the primitive triangle A B C is constructed as in the modern system. Take A D m A D' =r 45 yards, and draw the perpendiculars D E, D' E' rz 8 yards. In joining the extremities E, E', of these perpendiculars to the points F, F', where the i)riniitive triangle intersects the counterscarps, the master line of the ravelin is obtained. The parapet of the cavelier is only 4 yards thick, and is supposed to be suffici- ently strong to resist ricochet ; there is no rampart, the banquette is destined for musketry, and its slopes descend to the tcrreplein of tlie ravelin. The ends are retained by walls sufiiciontly thick to bear the pressui-e of the remblai, but which may easily be destroyed by the artillery of the place, should the enemy attempt to form a lodgment. Two flights of steps placed at the extremities of the faces lead to this banquette. General Dufour calculates that after the breach, the parapet of the lodgment will be 3 yards lower than that of the cavalier, and to render its establishment difiicult or even impossible, he puts in this cavalier some beds of stones or fragments of masonry, which he covei's witli 2 to 3 yards of earth to protect the defenders from the siilintcrs. The ravelin is 22 yards wide, 2 yards wider than in tlie modern system, to aft'ord room for the construction of ramps, 3 yards wide, and at slope y for the passage of artillery. The escarp is 24 feet high. The ditch 20 yards wide, has its coun- terscarp parallel to the sides of the primitive triangle, and its bottom is 6 feet above that of the main ditch. Tlie command of the ravelin over the covered way is 6 feet next to the salient, and 3 feet at the extremities of the faces. The reduit of ravelin, is separated from the ravelin by a ditch 10 yards wide and 6 yards deep, its bottom being 6 feet above that of ravelin, and 12 feet abo^e the main ditch. The faces ai-e parallel to those of ravelin, and the gorge is traced parallel to the curtain on the line M.N that joins the points of" intersection of the counterscaiiJS of the main ditch with that of the reduit. The flanks, 25 yards long, are traced in taking 30 yards off the face, and 20 off' the gorge, as in the modern system. This reduit has no rampart, in order to leave no available space to the enemy ; the slope of bancjuette descends to the terreplein whicli is oil a level with the ditch. The flanks are more loop-holed walls 6 yards wide, and 3 feet thick ; the loopholes are at 9 feet from the ditch, and a banquette enables the garrison to use thcni. Eacli wall has a door, wide enough for the passage of artillery, leading to the ditch; it is closed when the enemy has taken the ravelin. As these flanks cannot be seen from the lodgments, they have nothing to fear from artillery. This disposition.of the reduit permits the defenders to hold the redoubts of the re-entering places of arms, after the fall of the former, since their teneplein cannot be seen. The reduit has a command of 6 feet over the ravelin at the salient, and 1 ^ feet at the real-, so that its plane of defllatle passes above the loilgment of the cavalier. The covered way is 10 yards wide, and has four traverses. The three first ai-e 3 yards thick, and the last 6 yards. The first is traced as usual, the second is also oblique, in order to enable the cavalier to see its exterior slope ; its position is found by dividing into 3 equal parts the length of the counterscarp contained between the first and last traverse, and directing the crest to 10 yai'ds from D. The last, however, can only be traced after the re-entering place of arms. The jian-coupe at the sdieiit is 10 yards long. The crochets are made as in Vauban's, and are revetted; they serve for the passage of infantry, whilst artillery ascend by the ramps constructed at the gorge of the places of arras. There is no pali- sading except at the salient In order to close the ti'ouee of ravelin, Gen. Dufour unites the coupure of ravelin with the reduit of re-entering place of arms, so as to form only one work, the escarp of which is protected by a glacis erected in the ditch. To trace this reduit, join the salient A of the cavalier to a point O on the capital of the bastion, at 25 yards from the flanked angle : it gives the counterscarp of the exterior face, while that of the interior one is obtained by drawing the perpendicular P Q to the side of the primitive triangle. Parallel to the counterscarps and 7 yards in rear ai"e the escarps. The cavalier protects the exterior face against ricochet : the ulterior one is covered by a bonnet at the salient, 3 feet higiier than the parapet, and by a traverse of equal command along the face and in the ]irolongatioii of the parapet of the ravelin. The bonnet covers 3 guns, destined to flank the ditch of the ravelin, and to contribute, with those on the bastion, to oppose the construction of batteries at the salient of the covered way. The traverse covers 2 guns that sweep the terreplein of ravelin. To prevent the enemy, once established on the cavalier or in the reduit of ravelin, fi-om taking the exterior face at reverse, this face has a slope of 5 feet to the rear, and the parapet of the interior face has the same command at the salient of the reduit of the ravelin. The ranq)art of the interior face must also sloj)e to the rear to insure the defilade. The escarps arc 422 PRINCIPAL BASTION SYSTEMS. 18 feet higli, and the parapet has a command of 9 feet. The rampart, including the interior slope, is 10 yards wide, and is supported along the interior face by a revetment, which the defenders can easily destroy by artillery if the enemy at- tempts to make a lodgment: on the exterior face, which does not present a favourable position to the enemy's batteries, an earthen slope is sufficient As in the reduit of ravelin, the terreplein is on the same level with the ditch. A large ramp along the revetted face leads fi-om that terreplein to the rampart. A postern, on a level with the terreplein, leads to the ditch, and from that ditch a ramp leads to the covered way. Another ramp at the gorge of the reduit, leads fi-om the main ditch to the terreplein, thereby aflFording a short passage to artillery from the place to the covered way. The revetment wall of the extremity of the interior face is produced to the main ditch in order to prevent surprise, and to protect the work against the musketry fire from the reduit of ravelin. A gate opposite the ramp enables the garrison to communicate with the ravelin. In the ditch of the ravelin, a traverse forming glacis protects the escarp of the reduit of the place of arms against breaching batteries, which the besieger may construct at the salient of the covered way. A passage of 3 yai-ds is left between this glacis and the escarp of the ravelin to prevent the enemy from escalading the latter, and to enable the garrison to communicate between the ditch of the ravelin and that of its reduit. A strong gate closes the passage, wdiich is covered bj' the shoulder of the cavalier, and a little gallery constructed under the traverse flanks that gate. The re-entering place of arms is traced fi-om the point li, the intersection of the counterscarps of bastion and ravelin, as a centre with a radius 10 yards longer than H Q. Two circular sally-ports lead to the glacis. The crest of the glacis of the bastion and of the re-entering place of arms, has a command of 1^ feet over that of the glacis of ravelin. The enceinte in this system can sweep the re-enter- ing place of arms with its guns. This system possesses many advantages. The besieger cannot breach the enceinte from the crowning at the salient of the covered way of the ravelin ; the reduit of the re-entering place of arms is large and well calculated to dispute the possession of the ravelin, and as it does not mask the fire of the bastion, the en- ceinte can sweep the glacis ; the ditch of that work is flanked on both sides, viz., by the bastion and by the flanks of the reduit of the ravelin ; the narrowness of the terreplein of the outworks does not afford room to the besieger for the con- struction of batteries, and he must crown the covered way of the bastion in order to breach the enceinte, a great advantage for the defence, since the garrison will have only one breach to defend. The defence on this system is calculated to last 40 days- The communications are easy and practicable to all arms, thereby fiicilitating tlic sorties. The enemy, compelled to construct direct batteries, will CIIOUMAKA. 423 consuino more ammunition, he will besides lose time and labour in giving his trenches a great command, since the place has a great relict", and the defence being siinphfied will become more energetic. The outlay is not greater tlian in the modern system, because if on the one hand the mass of the cavalier and an increased relief necessitate greater remlilais, on the other there is a saving of 2000 cubic yards of masonry. It is to be remarked, however, that the cavalier prevents the defenders from placing artillery at the salient of the ravelin, where its presence is so important, and that the reduit of the ravelin has no room for guns. (389). Choumara (489). In 1827 Choumara published some " Memoires sur la Fortification," a new and enlarged edition of which was reprinted in 1847. It is therefore to the former date, and even to 1824, when his memoires were com- municated to the corps of Engineers, that this remarkable volume should be re- ferred. This priority of date is important, as between 1827 and 1847 spurious imitations and j)lagiarisms were brought before the public. This work has not been translated into Englisli, and should it be, Ijut few officers of the line could thoroughly understand its contents, and apjircciatc! its gi-eat value, through want of a knowledge of that branch of mathematics on which the drawing of plans is based. To those of my readers who are already conversant with military drawing, and who are acquainted with the elementary principles of Fortification, I cannot too strongly recommend a serious perusal of these Memoires, for the science at the present time docs not extend any further. Instead of offering a new system, as his predecessors too often did, Clioumara proposes new and general principles, apiilicable to all the systems either [)ast, present, or to come. (390). The two chief principles are : 1st. The reciprocal independence of the parapets and tlie escai'ps. 2nd. The construction of an interior glacis in the ditches. That which distinguishes Choumara from other writers on the science, is the objection he has to supersede everything by the introduction of a new system ; his constant endeavour is to modify the fortresses already extant, in order to increase their power of resistance. He always aflirms that he has no system. In fact he has given principles, deduced consequences tiierefrom, and generalized them ; and, although he has grouped together a few combinations susceptible of presenting a formidable ensemble, yet he by no means considers them as an in- divisible whole ; these combinations, he says, can be adopted either partially or wholly, according to circumstaiSces, and the engineer may select the special improvement required for the particular fortress entrusted to his chartrc. Starting from tiie two principles above mentioned, he leads us to the discovery uf various combinations arising thcrefroili, which may be employed in tlic 424 PRINCIPAL BASTION SYSTEMS. organization of a j)lace from the most simple case, that of an enceinte without citlier outwork or interior intrcnchment, to the most complicated one, that in which, having at disposal both space and money, a complete fortress can be erected, having — 1st. An enceinte, with an interior glacis in its ditch. 2nd. A general intrcnchment against an exterior attack, composed of the com- bination of the military buildings with bastioned towers, forming themselves good bomb-proof barracks, and so disposed as to favour the interior defence, should the enemy enter the place. 3rd. A ravelin, with a ditch and its interior glacis. 4th. Some redoubts in the salient places of arms of the bastions and ravelins, whose covei ed way also contains an interior glacis, forming at will a basin of inundation, that is calculated to oppose the construction of the batteries destined to breach the salient redoubts, to submerge the descents into the ditch, the mines, and even the trenches on the exterior glacis, thus transformed into a de\ersoir. (391). A striking featm-e of Choumara's principles is the superiority which their application tends to restore to the defence over the attack. With him, in fact, the escarps are only destined to prevent an attack by surprise ; they are the permanent part of the fortification, whilst the parapets constitute the temporaiy or moveable part. The masonry forms the enclosure of a field of battle, in which the garrison will fight at advantage, throwing up earthen parapets now in one direction, now in another, following step by step the progress of the besieger, counter-attacking him by the construction of new parapets varying with the circumstances, and assuming an active part instead of a passive one. Let us pass in review some of the consequences which we may derive from the first principle. (392). The parapet may be made circular at tlie salient of the bastion, so as to fire on the approaches carried along the capital. Tlie advantages of fronts in straight line (30a) arc at once obtained in tracing the parai)ot on directions whose jirolongations are intercepted by tiic ravelins. CIIOUJIAKA. 425 Clioumai'a recommends the omploymeiit Dt' the space intervening between this parapet and the escarp, for a chemin des rondos for musketiy ; and in order to protect its defenders a bonnet or a ti-averse is constructed at the salient. The parapets of bastions maybe traced perpendicular to the ditih nf the ravelin, wliich they flank more effectually, whilst they afford new flanks from which the lodgment of the besieger can be seen, and fire dii-ected against his counter- 1 latteries. (393). The flanks, being withdrawn farther from their escai-p, can be made longer, and receive more artillery than the enemy can place in his counter- iiattcries. Thus a line di-awn from the last gun of the crowning to the shoulder of the escarp, will limit the improved flank. The curtain itself, being drawn in, will permit the construction of flanks from which fire can be directed on the approaeiies. PRINCIPAL BASTION SYSTEMS Fig. 738. (394). The defence may even assume an enormous superiority of tire if several flanks are placed behind one another, as represented in the left bastion, and in this profile. This alteration, Choumara assumes to be practicable, even diu'ing the siege, provided earth has been reserved for the purpose. Additional enceintes may be formed in tlie manner represented in the last [irofile, and if timber is abundant, a system of blinded batteries, giving several tiers of Fig. 740. CIIOUMARA. 427 .nns, may be organized all round the enceinte; or at those points where an over- whohuin- fire of artillery is judged necessary, as in the right bastion (hg. 738). The parapet of the bastions and ravelin may, in fact, assume any such tracmg as the requirements of the defence render most advisable. 42>< PRINCIPAL BASTION SYSTEMS. (395). All these improvements, applicable to any system, do not imply any alteration in the masonry of the place. When, however, the engineer is at liberty to alter the enceinte, Choumara recommends the withdrawal of the original curtain A B as fai- as C D, the extremities of the retired flanks : owing to tliis modification, the tenaille can be constructed so as to mount artillery on its flanks ; and the parapet of its faces, besides giving musketry fire on the covered vvay, can protect the defenders of the flanks against ricochet. This tenaille is only revetted along the face, and that part of the gorge which is parallel to the flanks of the bastions. Tt may also be caseniated so as to receive additional guns. (396). The construction of a glacis in the ditch prevents the besieger from breaching the enceinte from the salient of the covered way, and closes the ti'ouee of the ravelin. In order to prevent the enemy from advancing in sap along the ditch of the ravelin to crown this glacis, it may be constructed in the shape of a traverse. Both profiles may be adopted simultaneoush' ; the former at the salient of bastion, the latter along the gorge of the ravelin and faces of bastion. i (397). With regard to the erection of new fortresses, Choumara has proposed important alterations in the ordinary methods, and we represent (fig. 752) the outline of a front in which these modifications arc indicated. Setting aside the defence by musketry alone, he reconnnends the lengthening of the front to 500 or even 600 yards, in ortler to obtain capacious bastions, the CIIOUMAliA. 420 only ones which can be properly retrenched: it is for tlie same reason that he iiives to the curtain the niinimiun lengtli. He strongly insists upon tlic cheniin- (les-rondes as destined to pre\ent the parapet from falling, and rendering the breaches practicable. At the salient of the bastions he establishes casematcd traverses 20 feet liigii, to arrest the ricochet : they can be destroyed when aliaiuloned by the defence, and they give fire on the cajntal as well as on the hulgnient at the salient of the ravelin. Such traverse may be provided with a parapet on the top. They occupy less room than the twelve ordinary traverses which the faces of bastion would require. (398). The rotrenehnicnts in the bastions are organised in such a manner that the capture of one bastion is not attended witii the fall of the place. Every bastion has a retrenchment towards the interior of the place, consisting of a bastioned front A P> C D, with imrevetted counterscarp E II K, and a ditch 14 feet deep before tiie curtain and 24 feet at the extremities E and H. A glacis and narrow covered way surround the ditch. The curtain of the enceinte in D D', A A', has no parapet, and the waH is loopholcd to procure a view of the dead angle between the flanks and the tenaille. The bastions of the retrenchment have orillons whicii i>rotect the chemin-des- rondes of their flanks. Under the curtain, s(^<'eral casemates 60 feet by 20, serve 430 PRINCIPAL BASTION SYSTEMS. as magazines or barracks. They are 2 feet above the bottom of the ditch, and can contain 500 men. Each bastion can thus contain its ammunitions and pro- visions, and constitutes an independent work. A subterranean passage under the curtain establishes communications between the various bastions of the place which can mutually support each other. As for the bastions of attack, a reti-enchment towards the exterior is necessary, and Choumai-a provides for it. A ditch M N X P, 14 feet deep, in rear of the curtain B C, is revetted by a wall which from O to O' and P to P' is built under the terrcplein of the bastion, and connected with the wall SO', P'T of the chemin des rondes. It constitutes a bastioned fi'ont with orillons, and the defence can complete it when the besieger has begun his attacks and occupied the salient of the covered way of the ravelin. If the earth from the ditch is not sufficient, some is taken from the interior bastion, now useless, the wall of which only is left standing. This transformation, according to Choumara, will occupy 150 men during 3 days. A second retrenchment W Y Z V, not revetted, is constructed in rear. The outlay in the construction of these retrenclmieuts does not increase the total cost of a fortress more than one-eiirhth of Corniontaiiiirne's tracintr, and vet CUOUMARA. 431 the defence may be prolonged 24 days, viz., 9 days for each of the exterior rotrcnchincuts, and 6 days i'or the sinudtaneous attack of the isolated bastions. (399). The main ditch is widened to 50 yards, in order to give rooiu for a glacis that will leave a 16 yards passage between its crest and the escarp. The tenaille is traced as described before. The ravelin has, like the bastions, a chemin des rondes, a parapet with flanks, and a casemated traverse in capital. The gorge is not entirely revetted, and possesses a wide ramp destined to permit offensive returns. Coupures may be organised. The covered way consists of two distinct parts. The first ABODE slants from the counterscar]) to the exterior, forming glacis, and also from the counter- scarp of the main ditch towards the saHent, where it forms the ditch of the salient rcduit. It covers the escarp of the ravelin against the batteries of the crowning. The second part is an ordinary covered way with glacis, which contains caponiers C, C, and no traverse. The reduit of the re-entering place of arms is provided with a ehcmin des rondes, and a circular' parapet ; the counterscai'p is not revetted. Sometimes the two adjacent reduits are replaced by one reduit of greater dimension, as in II. The salient place of arms has a reduit of the same nature, the faces of which are protected against enfilade by traverses t, t'. The communications consist of ramps practicable to all arras. (400). These modifications are calculated to protract tiie siege. It is easy to 432 PRINCIPAL BASTION SYSTEMS. see that the saliency of the reduit BDC increases the perimeter of the first parallel by nearly 300 yards, and as this reduit requires counter-batteries to be silenced, the second parallel will not be completed as soon as usual. The progress of the saps will be slackened by the artillery of the defence no longer destroyed by ricochet ; and the construction of the third parallel will also be retarded. The approaches against the bastion cannot be commenced until after the salient reduits are taken; and the crowning of the salient of the covered way, also rendered difficult, will not, according to Choumara, be finished before the thirty-seventh night. It is now, however, that the difficulties which the besieger must surmount become serious. To take the place, he will have six distinct breaching batteries to constmct: 1st, against the salient reduits; 2nd, against the reduit of the re- entering place of arms, and the ravelin ; 3rd, against the bastion ; 4th, against the first exterior retrenchment ; 5th, against the second exterior retrenchment ; 6th, against the isolated bastions ; and, as he cannot construct them simultaneously, but is obliged to erect them in succession, the defence will be considerably protracted. The breaching batteries against the salient reduits would be exposed to too gi-eat a fire from the collateral works, from the reduits of the re-entering place of arms, from the bastions, and even from the work itself, if constructed on the glacis, as usual : they must be erected in the ditch itself. The ravelin is breached by a battery constructed on the salient reduit, and tlic reduit of the re-entering place of arms by a battery erected opposite its salient. As this reduit is seen at reverse from the ravelin, the defence may, by an offensive return on the ravelin, oblige the enemy to abandon the former. The breaching batteries against the bastion, as well as the counter-batteries, must be constructed on the interior glacis of the ditch, and the overwhelming fii'e to which they are exposed affords a fair chance to the defence ; in fact, there is scarcely room for more than six guns in the counter-batteries. However, supposing the bastion of attack carried, there remain still the exterior and interior retrenchments. Choumara calculates the dm-ation of the siege at 112 days: it is, perhaps, too much, yet there is no doubt that the defence will be very much lengthened, nearly three-fold, whilst the expenditui-e is not much increased. We cannot follow Choumara in all the details he gives. Let it be sufficient to say, that he has rendered to the defence its former superiority over the attack, and that by applying part of these modifications to the old fortresses, the very worst of them evidently become superior to the best tracing hitherto known. To earthworks he chiefly entinists the active part of the defence; and the recent events in the East speak so loudly in favour of his ideas, that it is needless to dwell longer on their vital and obvious importance. (401). General Ilaxo (490) did not publish his system, but in 182r) he had HAXO. 433 a plan of it ongi'aveil, which ho distributed to somo French engineers ou condition of not rendering it public. Tlie li'ont is 360 j'ards long. Tlie perpendiculai' is only ,',, and tlie faces -j of the front. The flanks are perpendicular to the lines of defence. The bastions contain intei-ior retrenchments cntii-ely separated from the rear by a ditch. A chemin des rondes surmounts the scai-p of the enceinte. In tlie bastions the pai-apet is removed from tho wall so as to increase the length of the flank. In the left one, which is full, stands a cavalier, or high bastion, that carries two tiers of guns, the lower of which is easomatcd {k I'Haxo, 379). The tenaille is not revetted, and it has flanks that can mount three giuis. The salient of the counterguards is formed by the intersection B B' of the capittils, and a line parallel to the fi'ont, and at 45 yards from it: their faces arc 125 yai-ds long, and their flanks parallel to the perpendicular. They have a chemin des rondes, a coupuro, and a casemated battery in capital. The main ditch is 20 yai'ds wide. The ravelin is traced by measuring 17 yards oft' the shoulder angle of bastion to d, and describing from that point as centre, and radius 250 yai'ds, a circle which intersects the perpendicular in D, and joining D rf, D d'. It is thus made very salient. A casemated traverse is in ca])ital, and coupiu-es arc cut across its faces. , In rear is a reduit of the ordinary 434 PRINCIPAL BASTION SYSTEMS. outline, and behind it a casemated caponier or bastionet, the roof of which carries ten guns. The counterscarp of the main ditch is produced to witlun 10 yards of this bastionet, and in front of it slants a glacis g, g' which closes the ditch of the ravelin and that of the reduit. A double caponier in the main ditch leads to the bastion, and is joined to the flanks of tlie counterguards by an intei-ior glacis. The covered way contains traverses as usual: the salient place of arms has a casemated redan for a reduit The reduit of the re-entering place of arms is also casemated : one of its faces is perpendicular to the coiuiterscarp, tlie other parallel to it. This tracing, in which Haso has borrowed much from Choimiara, and in which ho has introduced a bastionet that reminds us of the caponier of Montalembert, is superior to that of the modern system, and yet not much more expensive than a front of the latter provided with permanent retrench- ments. Its siege is calculated to last fifty days, and there are five distinct periods of breaching batteries ; 1° against the reduit of the salient place of arms and the ravelin ; 2° against the reduit of the re-entering place of arms, the coupm'cs and the reduit of ravelin ; 3° against the bastionet and the counter- guard ; 4° against the retrenchment ; 5° against the bastion. The masonry is skilfully concealed from the -views of the distant batteries, and the chemin des rondes prevents the fall of the parapets. The command of the high bastion, 53 feet, interferes seriously with the defilade of the saps. The flanks of the enceinte have a good length, and those of the tenaille are well protected by the counterguards. These ai"e judiciously traced, well flanked, and defend the ditches of the ravelin, reduit and bastionet, &c. Their conpure, however, appears useless, because it can be breached at the same time. The retrenchments in the bastions are not good, because they diminish the length of the flanks. The gi'eat saliency of the ravelin is well calculated to take at reverse the approaches on the covered way of the bastion. The bastionet sweeps the interior glacis, and powerfully co-operates with the flanks of the inner works to impede the construction of the coimter-batteries. In the covered way the tracing of the re-entering rcduits is good, and the casemated batteries are an excellent model, for the details of which we refer to 379. (402). It is now time to forewarn mihtary students of a mistake into which they may easily be led. It is not in learning how to draw a great number of systems that they will acquire useful information. Let them peruse the details of several sieges, for this, above all, M'ill benefit them. It would indeed be a difficult task to stuff' one's memory with the never-ending systems daily proposed. We have examined these systems which are universally recognized as the PUINCIPAL BASTION SYSTEMS. 435 best, and intentionally loft aside a great many which have for a time attracted public notice. It is not long since new systems were proposed in this country by Messrs. Bordwine and Fergusson ; in Holland, by Major Mcrkes ; in Prussia, by Major Wittich ; in Spain, by Colonel Hcri'cra Garcia, &c. &c. If a student will venture into more systems, let liim investigate these as well as tiiose to wliich allusion is made in our concluding chapter. He will soon grow tired, and will perceive that they are not so much distinguished from each other by any essential difference as by their authors' names. Every one who has written on Fortification has given at least one system of his own ; three, however, is the favourite number. Marchi, an Italian engineer, in 1599, has, indeed, in a folio book, oft'ercd 161 diifcrent consti-uctions, which ho declares to bo his own, and laments the loss of others that were stolen from him ! Engineers, officers, architects, professors of mathematics, students, and even pupils, all have claimed to be masters of an art, tlie elements of which they did not ]3ossess. The claim was easily set up, since by taking the straight line and the curve an infinity of combinations ai"e to be made. Some have fancied that by multi- plying the Hanks they would attain their object ; the most moderate have proposed three Hanks, some fom-, others six, &c. Some will have two enceintes, others cut their works into a nmnber of small parts, hoping to strengthen the system by increasing its complexity. They all forget the cost, the force of the garrison, and the provisioning ; and each will assert tliat a fortress constructed according to his system is impregnable. Tiie outline of a system is undoubtedly an essential point, but it is not all. A determined gari'ison, ably commanded, will perform wonders even behind a wretched outline. Metz, in 1553, had but a single wall and rampart, and a dry diteii without bastions, yet Charles the Fifth, with 100,000 men, could not take it. The Castle of Mouzun, in Ai-ragon, a more barrack, garrisoned by only 100 French soldiers, resisted (in 1814) 3000 Spaniards for fom- months and a half! Vienna, in 1683, resisted three months the efibrts of the Turks; Candia stood out against them ten years ; Silistra with a Mussa Pacha, and Kars with a Williams, are still in every one's mind. Let us therefore beware of placing implicit confidence in any of the systems alluded to, and instead of attempting to build new fortresses, let us begin by impi-oving the old ones, whenever necessar}-. Alluding to the great number of systems. General Prevost Vernois says : " If we take into consideration the numberless systems of fortification which the human mind, or, if preferable self-complacency has invented, and which are with \erv few exceptions ncai-ly all equally absurd, we shall soon be convinced that nothing is more difficult than to produce a useful and rational imiovation. So K K 2 43(3 PRINCIPAL BASTION" SYSTEMS. difficult is this ai't, that no one can reach the summit : even the most vigorous minds require rest during the ascent. It requires an eye like that of Vauban or of Naj)oleon, penetrating as the eagle's, to find on a frontier the strategic point ; since such point is essential to a permanent fortification, and ought to be held by those on the defensive of whatever nature and however numerous the movements of the enemy may be. The sti'ategic point being chosen, it remains to determine the kind of fortification which is best adapted for it ; for there must be ' some plan of occupying this site preferable to any other ; and this necessarily depends on the configuration of the locality. The best adaptation is written on the soil ; but every one has not the gift to read it : we repeat, that without doubt, fortification is the most difficult of arts. The thorough engineer sees his foi-tress completely modelled on a plateau, a hill, a plain, or on a rock, just as a sculptor sees his statue in a block of marble ; nay, more, he also makes tlio best of nature's resources. Wo have twenty sculptors of the first rank, and yet the work of ages has given birth to only one Vauban. " The most difficult of all arts," says Fontcnelle, in his eulogy on this great man, " are those whose object is change, since this does not aftbrd to men of ordi- nary capacity the convenience of the application of certain fixed rides, but demands at every moment the natural and improved parts of a lofty genius. " This is all the more worthy of remark, because all the efforts of Vauban's suc- cessors have been directed to the imposition of types on us, and to reduce the art of the engineer to fixed rules and to processes of descriptive geometry. Destitute of the power of being engineers, they are desirous of making themselves savants. Now although descriptive geometry can teach the way to apply a plan of fortifica- tion, such as it is, good or bad, to a given locality, when certain conditions are given, yet it will never sujjply the means of determining what plan is the best and most suitaljle. " In painting and sculpture, fashion, caprice, the desire of varying combinations, and of exhibiting new ones, can load artists into not a few vagai-ies ; but these aberrations will not be of long duration ; tbey are always brought back to truth by a comparison of nature's objects with their representation. Now nature affords no perfect model of a fortification, none which can serve to correct our errors. If a military engineer is carried away by the most extravagant whims, there is nothing to point out to him their absm-dity. People do not under- stand it ; engineers generally profess the most sovereign contempt for every new system which deviates from the teaching of the school : on the other hand, there always exist in large assemblies, a very large proportion of idleness, indifference, carelessness, inaptitude, &c., and the indolent are naturally the \n-ey of active working men." CHAPTER XXIV. MONTALEMBERT AND CAENOT. (403). Despite all the improvements made in the bastioned system of fortifica- tion since tlie time of Vaiiban, there are j'et many important defects which liave induced some engineers to renoimce the bastion system altogether. They justly complain that : — the ramparts and the interior of the place are much exposed to vertical and ricochet fires, which ruin the artillery of the defence before the enemy reaches the covered way ; the reverse and ricochet fires render the flanks of the bastions almost untenable, although it is on them that the defence of the ditch and breach rests ; the communication between the enceinte and tlie out- works is badly organized, and i-enders difficult the sorties and offensive returns ; the ditches of tlie outworks form openings through which the besieger may breach the enceinte from a distance ; the parapet falls down at the same time as the wall when the breach is made ; the interior intrenchments are very difficult to construct at the moment of need ; the labour necessary to put the place into a state of defence and to keep it so during the siege is dangerous, exliausting and often impossible for the garrison to accomplish. SECTION I.— MONTALEMBERT. At the head of reformers is Montulembert (480), and although his systems have not been adopted, yet they form the base of the works constructed in Germany since 1815. We shall thei-efore say a few woi'ds on them. The chief object of Montalen^bcrt is to prevent the besieger from opening a breach, by directing against him a superior fire of artillery whenever he attempts to erect counter or breaching batteries. His fortresses may be called immense batteries. i (404). First system. In 1776 he pi'oposed to replace the bastion outline by the tcnaille tracing. The name of perpendicular fortification is given to this system, because the faces of th<,' re-entering angles arc perpendicular tn each other. 438 MONTALEMBERT. As the salient angles cannot be less than 60o, it is impossible to enclose a space witli less than 12 salients; with a greater number of tenailles, the salient angles become more and more open. Montalembert has not given any formula for the tracing of his systems, but he has published elaborate plans sufficiently accurate to give a complete idea of his methods. The following data will enable the student to construct the outline. The tenaille has faces A B =: B C :r 250 yards in our example, but their length may be increased with a range of musketry superior to that distance. The salient here = 60°. MONTALKMBERT. 439 This enceinte B" A B C B', consists of a cascniated gallery, one story high only, for artillery and musketry. The main ditch, 36 yards wide, is parallel to it. It is flanked by a casemated battery .J/B?/' having two stories for musketry and artillery, besides a i)latfurm on which artillery may be placed. It occupies 40 yards along each face of the re-entering angle, and also flanks the rear of the gallery. Beyond this ditch, which Montalembert supposes wet, stands a general comTe-face or counterguard E H D, 30 yards thick, consisting of a remblai for infantry and a loopholed wall. It is intersected by coupures. A wet ditch, 18 yai'tls wide, separates it from a covered way of 1 2 yards, and is flanked by a casemated battery r H ;•', of two stories for musketry and artillery, which also defends the rear of the loopholed wall, the faces of this casemate are 20 yards long. To defend the long branches of the covered way, and act as a reduit of re-entering place of arms, a lunette is traced: the gorge FLrrlOO yards, and the flanks LN=:20 yards, N0 = 22 yards ; the wet ditch and covered way surround it, and are of the same dimen- sions as those for the countcrguards, except round the flanks, where the ditch is not more than 10 yards wide. The ditch along the face is flanked by a casemated battery N O, two stories high. Inside these lunettes, a reduit having faces P Q. of 25 yards, defends the tei-replein ; it is a loopholed wall rendered bomb-proof by arches, and is preceded by a small ditch. The cohered way has no traverse and no palisades. Inside the general enceinte B" A B C B', Montalembert constructs for every salient a special counterguard ab of earth, 25 yards tliick, the crest of which is parallel to and 25 yards iu rear of the enceinte, and measures about 145 yards in length. A wet ditch 12 yards wide, defended by a loopholed wall df extends in rear of the counterguard. Eight yards behind this ditch is the exterior slope h s of the interior reti-ench- ment, which turns at a right angle to join the great battery B y' ; the foot m n of its ram[iart is at 30 yards from hz. A casemated battery for artillery and musketry z z', two stories high, and with faces of 20 yards, flanks the wet ditch in rear of the counterguard and the dry ditch that extends between its extremity and the interior retrenchment. At last a tower X, 1 1 yai-ds iu diameter and containing 24 guns in two stories, sen-es as a reduit. Its centre is at 30 yards from the foot of the rampart m n. A loopholed wall nins between the tower and a casemated traverset established on the rampart, and defends the terrcplein. A small ditch s is cut across the rampart before each traverse. The commands of these various parts are mai-ked on the following profiles where .r x represents the level of the country. The vaults of the casemates are pierced with cylindrical holes for the jiassage of smoke, and in the great casemate /I?//', little cliambers are constructed for tho infantrv, mider the floors of which MONTALEMBEKT. Fig. 755. Grv€Ur CaaemcUe the embrasures for guns are cut. As for the tower of this system, we shall have to enter into fiirther details respecting it hereafter. With regard to the commu- nications, the three casemates y^y' and z z, z' z' communicate by subterranean passages : a postern leads from the place to the interior of the great casemate, and two posterns to each casemate z z. Ramps lead to the rampart of the interior retrenchment, and access is given to the inner counterguard and the gallery of enceinte by a door in casemate z z. A postern leads from the re-entering angle of the great casemate to a bridge across the main ditch, from which the counter- guard is reached. On right and left, the passage continues through the casemate r H r', from thence a bridge leads to the terreplein of the lunette. A jjostorn under the face of the lunette leads to the covered way across a bridge. The bridge across the main ditch is constructed on two walls flush with the water and provided with banquettes. Should the bridge be destroyed by the besieger, the communication is not interrupted, and as it may easily be inundated the enemy cannot make use of it. MONTALKMllKUT. Fio. 760. (405). The partisans of this system most particularly insist upon the advantage wliich the defence acquires from the four distinct enceintes, the general countcr- guiml and its wall, the casematcd gallery with its inner counterguai'd, the interior retrenchment with its wall df, and the tower, which will compel the enemy to make four successive breaches before opening a passage. They claim that the main ditch is most Efficiently flanked by the 48 casemated gnns of the great casemate, and that the construction of counter-batteries against this work is next to impos- sible. The besieger has in fiict no space to erect a battery on the counterguard except near the salient close to the counterscarp ; room is found there for 1 1 guns, of which 8 only can be dii'ccted against the casemate ; these 8 guns opposed by the 48 alluded to, and by 24 more in the casemated gallery, could not fire a shot. The other advantages pointed out are that the casemated gallery will continue to defend the counterguard until it is entirely destroyed, that the defence will be veiy energetic fi'om the rapidity of the communications which facilitate numerous sorties, whilst the garrison and the ammunitions are in safety imder bomb-proof shelters. And lastly, that the approaches of the besieger will advance exceedingly slowly, because the great development of the counterguard will permit the defenders to employ three times as many guns as in the bastion system, and the casemates of the rear firing in capital over the counter-guard, will ricochet the zig-zags. They conclude by saying that the enemy cannot proceed any further than the covered way, and that the siege will become a blockade. On the other side, it is admitted that such would be the case if the casemates were intact when the enemy crowns the covered way, but it is justly argued that these casemated batteries will have suffered much from the ricochet battei'ies of the first and second parallel, firing over the general counterguard, and that if the defence commands more gtms than in the bastion system, the attack can also bring more. The method of attack proposed against this system, consists in counter-battering the casemates from the first or second parallel by ricochet ; the third parallel is con- structed at the foot of the glacis, the covered way of the salients is crowned, a fourth parallel runs between them, and a breaching battery is erected opposite the middle of the face of the counterguard. The covered way before the lunette is next crowned, the parapet of the lunette is breached by a battery constructed opposite its face. Once master of the lunette, the besieger constructs a batter)^ on tlie terreplein to open the wall in the re-entering angle of the counterguard, crosses the ditcli by a bridge, and jKissing tlirougli the breached wall enters the 442 MONTALEMBERT. counterguard by the breach previously made in its face. Batteries are next erected near the re-entering angle of the counterguard to breach the casemated gallery ; and if necessary, the mines will complete the destruction of the great casemate. Passing the main ditch by means of the masonry bridge, the besieger will enter the place, thus turning the inner counterguard and the interior re- trenchment. Such an attack would be folly unless the fire of the casemates had been silenced, and it is the question which now divides the French and tho German engineers. The latter contend that it is impossible to destroy the casemates by means of " feux courbes," and that it would require, to silence them, tenfold the time necessary to take a fortress of Cormontaingne ; and as one of the chief aims of Fortification is attained, they say that this system is superior to the bastion. The former assert that the great outlay of masonry and artiUery is pm-e loss, as the casemates can be destroyed at a distance, and all the flanking defence destroyed before it is called into play. Nothing but actual experience will end the discus- sion, but the recent improvements of artillery cainiot turn to the advantage of the casemates. '> (406). Second system. — In 1777, Montalembcrt published his second system. It is called polygonal fortification, and this name now applies to all fortification where the faces, forming salient angles only, or re-entering angles of small depth, are flanked by a caponier constructed in the main ditch. The following outline is proposed by Montalembcrt for a square, having an exterior side a 6 of 370 yards. On the middle of the front the caponier is con- structed by tracing its gorge about 4 yards inside the polygon, making it 14 yards wide, giving 16 yards to its flanks, and inclining the faces at 60°. This caponier, tlu-ee stories high, is destined to contain 27 casemated guns on each flank, besides a numerous infantiy. At 30 yards in rear, and parallel to the front, draw the curtain g h, and make it 64 yards long : from the middle of the front take the distances ic-=iid=zSZ yards, make cc'-:=dd'z=. 14 yards, and draw d'e, c'/ perjiendicular to the direction of the faces of the caponier : joining e g and //(, the enceinte add' eghfd ch is obtained. When the front to be fortified increases in length, the construction remains the same, so that the parts a d and c b are the only ones that become longer. The main ditch, 25 yards wide, surrounds the caponier and the enceinte: in front of it stands the general counterguard, which is 36 yards thick, except before the faces of the caponier, where the thickness is increased to 50 yai-ds, to give room for a defensive barrack M N P, loopholed for infantry, and two stories high. A casemated battery E H, two stories high, with a curtain of 18 yards, flanks of 20, and faces of 12 yards, is constructed in each re-entering angle to flank tlic ditch of the counterguard 15 yards wide. A lunette of 65 yards of MOXTALEMJiEIlT. 443 gorge, with flanks and reduit, is traced as in the first system. A covered way also surrounds tlio whole. ;^=i::'J n The cncointo from h to c, and from a to d, consists of a casemated gallery similar to that of the tenaille system: the casemates c c'f, dche three stories higli defend the ditch of the caponier, this is 12 yards thick: the parts //j, eg, called "retired flanks," are constructed like the casemated gallery, and defend the ditch in rear of the caponier. The curtain has, besides the gallery and above it, a loopholed wall 6 feet high serving as parapet. A casemated battery of three stories connected with the battery d d' e, has a length dv^:55 yards, and a thickness of 8 yards. In roar of the curtain stands a cavalier, the crest of which vuxykr is parallel to the curtain, and at 15 yards froiii it, and from the casemate: the crest v r is at IG yards from ,v y. The base of its exterior slope towards the place is suri-ounded by a small ditch, 8 yards wide, tlie escarp of which is 25 yards from the extremity V of the casemate. 444 MONTALEMBERT. At the salients of the front wc find an inner counterguard 25 yards thick, having its gorge at 37 yards from the enceinte ; 14 yards in rear of this gorge stands a casematcd barrack X Y ; a similar barrack z is traced in the prolongation of the face d V, and the centre of the space intervening between the two barracks is occupied by a tower. The inner counterguard is flanked by the casemate dN , and the small ditch in rear of the cavalier by the small caponier p. As for the communications, ramps lead from the place to the ditch at the foot of the cavalier, from which the counterguard, barracks and tower are easily reached. A postern leads from caponier F, under the cavalier to the middle of the curtain : there a bridge leads to the caponier, and two others to the re-entering angle of the gorge of the comiterguai'd. The rest of the communications i-emain the same as in the first system. In the following profiles, x x represents the level of the country. JSarroLCk 2 Xlcfo/um cfTcivcr vr m 'r r^ ^ I r^ MESB MONTAI.R^IUEin Kio. 7C5. 445 Cti%tma(f etl'd (407). The advantages claimed for the polygonal fortification in general arc that it is simple and allows of more unity and ensemble to the defence ; that it is economical, because for a given perimeter it encloses a larger space than any other tracing ; that the defence, being derived from the middle of the front, the front may be extended to 600 yai'ds without making the lines of defence greater than 300 yards ; that the enemy will thereby be comjjelled to execute an immense development of trenches : and that the fronts may be armed with an artillery 446 MONTALEMBERT. far more numerous than the bastion system. The defence of the ditch is secured by a sweeping fire ; and canister may be advantageously used, whilst it is too dangerous for the garrison itself, when the guns of the flanks of bastions attempt to employ it. There being no longer dead ditches, the fronts may be made as small as the irregularities of the ground may require. (408). It will readily be seen by the inspection of the pi-ofilcs that in this system in particular the third stories of the caponier, of the casemates d V, d e, of the flanks e (/, f h, of the curtain and of the barracks X Y and z, have a command over the counterguards, and overlook the ground of the approaches. They are intended to oppose the opening of the first pai-allel, and to destroy the ricochet batteries enfilading the covered way, the counterguai-d, and the cavalier. It is true that these batteries would soon be destroyed, since the besieger attacking the salient of the square would be exposed to 230 guns situated in the casematcd batteries of both fronts, and to 200 guns mounted on both counterguards, altogether 430 guns. But the besieger will not thus expose himself: he will counter-batter directly these high stories which are much exposed. They will soon be overthrown, and there will be no difficulty in reaching the glacis. The great caponier is badly constructed : the besieger, once master of the counter- guard, can erect batteries and counter-batteries opposite the salients of the square, and take this caponier between two fires, the defenders being exposed to the projectiles entering the embrasure, both in front and rear. We might also repeat what we have said of the effect of the ricochet fire, but setting aside the question, we can object against this system as well as against the first: the excessive accumulation of casemates; that the walls are too thin, the armament required too considerable ; that the defenders, constantly under cover, dread the open air and become timid, and that the casemates pi-esent the defects already alluded to in No. 378. The other details of construction wo do not name, because, in giving the systems of Montalembert, we bad only in view to explain his principles. (409). Montalembert also proposed a circular fortification. It consists of two casemated enceintes A A, B B (fig. 770) four stories high, sur- rounded by a tenaille enceinte two stories high. A shallow ditch with a cunctte in masonry, and a covered way with re-entering places of arms surround the whole. Caponiers for musketry 7n,m, flank the interval between the enceinte; p,p, are powder magazines. This fortification is not practically possible : every one can see that the high casemates of the enceinte B B are doomed to destnxction at the very onset, and that the effect expected from their immense armament is but an illusion. MONTALEMBEKT. Fio. 770. 447 -^: (410). Before taking leave of Montalembert we may say a word about his towers, which have been imitated by German engineers. Their base consists of tenaillcs having salient angles of 60°, and re-entering angles of 90o. These tenailles support arches of greater or less dimensions, accoi'ding to the size of the tower, and under the middle of these vaults redans of 90° salients flank the faces of the tenailles, so that every point round the foot of the tower is seen by the defenders. With such angles, the base of the tower must contain at least twelve salients. Montalembert gives 60 feet diameter to the smallest, and 144 feet to tlie largest tower with twelve redans. For a greater diameter the number, or the salicncy of the redans, must be increased. When the diameter = 144 feet, a second tower can be constructed inside the first, when 201 feet, there is room inside for two other towers. MONTALEMBERT. FlO. 773. We represent here a double tower, the diameter of the larger being 144 feet. The tenailles are loopholed for musketry. Ramps lead to gates a a placed in the re-entering angles, and from thence through other doors bb to the interior of the ground floor. The exterior wall is supported by the arches of the re-entering angles : j)illars rise from the foundations to the platforms, whore bomb-i)roof CARNOT. 449 vaults connect them. The casemates m m of the inner tower are loopholecl for musketry to defend the interior of the casemates of the large tower. The ])latforms of both are pierced with embrasures for artillcrj^ and a cu[)ola for iufantr}', occupies the centre of the platform of the inner tower. A winding staircase connects the casemates in each tower. Powder magazines and cisterns are placed in the cellars. Such a tower is ai-med with 72 guns ; and as the superior platform is 46 feet above ground, Montalembert expects that the besieger will be much delayed in the construction of his approaches, and jirevented from constructing his breaching batteries. This will not, however, bo the case, because the superior stories ot such a tower will be destroyed from a distance. SECTION II.— Caunot. In 1810 Carnot proposed to base the defence of fortresses on sorties and vertical tire (486). (411). In order to make a vigorous resistance, he recommends frequent or almost continuous sorties as soon as the enemy has consti'ucted his third parallel, and to render them more rapid and easy, he suppresses the revetment of the counterscarp of the ditch, and replaces it by a gentle slope. As the enemy will be compelled to maintain strong covering parties in this third parallel, Carnot proposes to have at the salients of the front of attack some casemated batteries of mortars, that will pour a shower of projectiles on the crowded parallel. The l)esicger, he thinks, will suffer so much that he must withdraw to the second or first parallel, and cover his saps by small detachments only, in which ease fm-ther sorties will have a fair chance of arresting the progress of the attack. Carnot exaggerates the effects of vertical fire. As a 12-inch mortar tlirows a shell of 150lbs., he reckons that it will throw 600 shots of jib. Placing two mortal's at the salient of the ravelin and of the two bastions of attack, he calculates that 3600 shots wnll be fired simultaneously. Supposing that one shot out of 180 disables one man, he finds that every discharge will kill 20 men, or 2000 men a-day for 100 rounds. Since the besieger employs generally ten days from the third parallel to the breach, lie will thus lose 20,000 men ! This calculation is wrong, because it requires more than 180 shots to hit a man, and even then the momentum of a {lb. shot in falling is not sufficient to disable him. Hence it follows that the enemy will not be prevented from keeping a numerous guard in his third parallel: the sorties will have no longer to deal with weak detachments, and, in a word, the whole tlieory falls to the ground. G O 450 UARNOT. As his systems contain several peculiarities which have been applied to recent constructions, we shall pass them in review. (412). First System. The side a a of tlio pokgon = 370 yards. Through the points a, w, called the centres of the bastions, draw the capitals A S, a s'. On the middle of a a' erect a perpendicular Ab=:29 yards, and the point B will \ be the centre of the tenaille. On l)oth sitles of A measure A f=zAc'=:82 yards. Tlirough b draw the lines of defence c d', c d. At c and c' draw cf and af perpendicular to the lines of defence, they will represent the flanks of the bastions. On the line of front, ai a, take c h z=z c' li =z 50 yards : these give the revetted gorges of the bastions. Through h and h' draw parallels to the capitals: these give the direction of the retired flanks, which are 30 yards long. The escarp 1 1' of the curtain is drawn parallel to and 8 yards from a a'. The magistral of the enceinte is thus determined dfc h 1 1 h c'f d'. The general retrenchment is parallel to the curtain. Its loopholed wall in vi', .50 vards from the escarp / V, is limited in m and m by the prolongation of tiie CAIiNOT. 451 retired flanks ; and »n n = wi n' rz 25 yards, measured on these dh-ections, are tlie flunks of cuseniated batteries, tlie front walls n n, n' w, of which are described with circles, having their centres on the capitals, and their circumference tangent in 11 and n' to lines parallel to the front. Tlie crest is parallel, and 20 yards inside. The tonaille is traced on the lines of defence, and is separated from the Hanks of the bastion by a ditch 10 yards wide. The ditch before the bastion is 12 yards wide, and its counterscarp is parallel to the faces. The cavalier is traced with its flanks o p, & p, perpendiculai' to the faces of the tenaille, 50 yards from the centre : they are 60 yai'ds long ; the gorge is traced on the counterscarp of the ditch of bastion ; the faces p r, p' r, are deter- mined by the lines/ jw, /' p', which join the shoulder angles of the bastions to the extremities p p' of the flanks. The counterguards s t, s' (', 2-t yards thick, are terminated at 12 yards from the flanks of the cavalier. The ravelin, also 24 yards thick, is traced in describing an equilateral triangle on a a' : its faces terminate at 12 yards from the counterguard. The counterguard and ravelin are surrounded by a ditch 12 yards wide, and beyond this is the countersloping glacis 50 yards wide. A caponier or ramp leads from the terrcplein of the tenaille up to that of the cavalier. In the profile the lines x x represent the level of the ground. 452 CARNOT. Fig. 780. Ttamfi e/ rapn It will be seen that the bastions arc surrounded by a loopholed wall masked by the counterguards : it is 24 feet high, 6 feet thick, with arched recesses on the inner side, and a chemin des rondes 6 feet wide. The gorge alone is unrevctted, to facilitate the sorties against the lodgment of the besieger. On each wing of the curtain, along the retired flank, is a postern, which establishes the communication between the ditch of the retrenchment and that of the curtain. Another postern in the retired flank leads by a flight of steps to a little yard lilv, 12 yards wide, situated on the level of the ground and surrounded witli a loopholed wall to give flank and reverse fire on the enemy attempting to attack the retrenchment ; it contains also two guns in embrasure behind /( I to flank the ditch of curtain. The interior retrenchment is provided with a detached wall 36 feet high and 6 feet thick. It is 9 feet thick in tho salient parts, n n, n' m. It has also arched recesses and a chemin des I'ondos, which communicate with the interior of the place by posterns constructed under the ramparts. In the salient parts n n, m n', the lower row of loopholes is destined for hand mortars, to fire at the lodgment of the bastion. On rear of these salients stand tlic casomated batteries n my, n m' y', composed of vaults open both in front and rear, to facilitate tho egress of smoke; each vault contains 2 mortars to throw stones on the lodgment of the bastion ; and the extreme piers m n, m' n', are pierced with three embrasures for three guns flanking the ditch. We have not represented in the plan the three batteries of mortars at tho salients of ravelin and bastion, which Carnot recommends for the front attacked, nor a casemated battery of guns in the circular parapet of the retrenchment, which he intends to fire at ricochet against the zig-zags in capital, and at point blank on the lodgment of the bastion. (413). Carnot claims for his system a great economy in the first outlay, a gi'eat dm-ability for his walls ; and as he dispenses with the covered way and its enormous palisading, and has a strong interior retrenchment ready, there will bo a gi-eat diminution of the labour usually required during the siege. The defence, he thinks, will be protracted, as the high rampart commands, and plunges the approaches ; tlie parapets independent of their scarps cannot, in falling, aff'ord a practicable breach ; the great batteries cannot be seen or destroyed either by ricochet or vortical fire; the men are well sheltered under the arched-recesses ; CARNOT. 453 the countcrguards oflFor but a narrow aim to rieochot ; and tlie counter-sloijing glacis exposes to jjlunging views any sap which the besieger might carry through. All these advantages, backed by the sorties and vertical fire alluded to, appear to Carnot cxti'cmely superior to those of the modem front. It is not, however, the case. The detached walls arc excellent to prevent the escalade, but they may be breached at a distance by vertical fire, so that the ramparts of earth behind them can be ascended. Supposing that the besieger proceeds with regular attacks, we have already said that, after the consti-uction of the thii-d parallel, he will not be compelled to withdraw on account of the vertical shower of projectiles ; and, as for the sorties, he can construct batteries at the salients of the glacis to bi'each the faces of the bastion and the flanks of the cavalier, and at tlic same time sjiaro a gun or two to fire grape sliot into the nai-row ditches from which the sorties must debouch. A fourth parallel, connecting the crowning of the glacis, will render the sorties still more difficult, especially if these batteries ha\e been sm-rounded at night by chevaux-de-frise, trous-de-loup, &c., that delay the gai-rison and give time to the guai'd of the foiu'th parallel to come up. The ravelin does not seem necessary : it obliges the enemy to commence his approaches at a greater distance, and covers pai-tly the debouchc through which the sorties must pass, but it may easily be breached by live shells or mining, and as it is unrevetted both in front and rear, and contains only a feeble garrison, it may be stormed in all directions. The cavalier, one of the chief featui'es of the system, masks the fire of the collateral bastions, and as it is mu-evetted, it may be assaidted at the gorge. Once master of the cavalier and tenaille, the besieger can employ the mine against the counterguard without being molested, and make u wide opening through it: a battery constructed opposite that point in the crowning of the glacis will breach the bastion. In the bastion the enemy finds space to construct a battery against the casemate : he may suffer from the fire of the mortai-s and pierriers, but he can emjiloy blind frames ; and as he has room to place a sujjerior artillery, the casemate is too small to resist long : the battery in the circidar rampai-t will not resist long for the same cause. Tliis system does not, therefore, bear investigation : nevertheless, the detached walls, the comiter-sloping glacis, and the casemated mortar batteries, have found numerous advocates, and are frequently employed. It is but just to add, that these casemates have been borrowed from a work published in 1781, by Virgin, a Swedish engineer. (414). Second and Third Systems. The first system of Carnot was intended for a flat country, where water is not found above 12 feet in depth. The second is destined for a marshy country, where excavations cannot afford great remblais. It is the tenaille outline of Montalenibert. The interior retrenchment consists of a loopholed wall a h a, the salients a a of which are 200 yards ajjart. It has no 454 CARNOT. Fio. 781. rampart behind, and is provided with two stories of arched-recesses. The ditch that suiTounds it is 12 yards wide. At the re-entering angle is a casemated battery C C, in which C D rz C D r= 48 yards. The front walls be, be' arc pierced with five embrasures for the defence of the ditch ; and the platform is organised for 16 guns. The enceinte ded', 40 yards thick, has no revetment; it contains traverses B, B', 12 feet thick, near the salient, behind which a few mortars may be placed: the vaulted passages^ v serve to place the boats under shelter. The tenaille, 25 yards thick, is surrounded on both sides by a ditch CARNOT. 455 12 yards wide, and has wings 120 j'ards long, measured on the gorge, to cover tlie enceinte beliind the extremities of tlie counterguards. These have the same thickness as the tenaille, and arc preceded by a ditch of 12 yards and a counter- sloping ghicis of 50 yards. A doulile caponier 36 yards thick, with a passage mm 8 yards wide, connects tlie tenaille with the place of arms okh! o' : this is serviceable during the sorties. There is a ditch of 8 yards width between the counterguards and the caponier : the traverses A A' are similar to B, B'. The flanks k, o' k' of the place of arms =: 40 yards, the faces k k' ^z50 yards. In the third system, intended for mountainous countries, the ditches are dry. The interior retrenchment is the same as in the second system. The enceinte is protected from escalade by a detached wall 18 feet high: it contains several posterns for the communications. In the re-entering angle there is a little yard y, Tenaille. Counterguard. the faces of which flank the diteli with three guns. The tenaille is surrounded 45(1 CAKNOT. in front and gorge by a wall of 18 feet. The counterguard, caponier, place of arms, glacis, &o., are the same as before. Very little need be added. With wet ditches, the sorties made from the place of arms cannot be so numerous as Carnot requires them, and they debouch from a point much exposed to the batteries of the besieger. The place of arms, which is not palisaded, is exposed to be stoi-med. The caponier and the long wings of the tenaille mask the fire of the enceinte, and the ditch has but a weak flank defence. I I ^ CHAPTER XXV. GERMAN FORTIFICATION SECTION I.— German System. The engineers of Germany, Prussia, and Austria, have adopted several of the ideas of Montalembert and Ciu-not, such as the polygonal tracing, the caponiers, the casemated batteries, the detached walls, and the countersloping glacis. All the fortresses they have built since 1815 present common features, and the name of German System has been given to the ensemble of their disposition. It shoidd however be understood, that the merit of these innovations is not universally acknowledged on the right bank of the Rhine. Some engineers in fact object to tlie countersloping glacis, others to the detached walls, and some reject both. (415). The fortifications of Coblentz may be selected as a type of the new method. Tlie annexed tracing (fig. 787) is that of a front of Fort Alexander 458 GERMAN FORTIFICATION. (fig. 786) according to the SancUiurst course. The exterior side A A' =: 510 yards : bisect it in O, take tlie perpendicular O P = ,l of the side, and draw the line of defence PA, PA'. The counterscai'p of the main ditch is parallel to the lines of defence, and at a distance of 30 j^ards from it. The ravelin is obtained by bisecting the lines of defence in C C, taking P D =r P C =: P C', and joining D C, D C. The ditch is 18 yards wide. The demigorge PS, PS' of the caponiers 18 yards: the flanks L S, L' S' are perpendicular to the Imes of defence, and are terminated at the counterscarp of the main ditch ; the faces T L and T L' are next dra^vr^ parallel to those of the ravelin. The counterscarp of the ditch in front is 30 yards from the faces. The top of this counterscarp produced intersects the lines of defence at E E', and the flanks E H, E' H' of the enceinte are traced perpendicularly to the prolongation of the faces of the caponier. A parallel to the side A A' drawn through the salient D of the ravelin, will give in B and B' the salients of the couuterguards, the faces of which are directed to the salient angle T of the caponier. The ditch in front of them is 18 yards wide. The covered way is replaced by a countersloping glacis 20 yards wide, and a glacis of vai-iable width. The profiles give the command of the various parts. Counterguard. The caponier destined to defend the ditch contains two stories of casemates ; each flank thus mounts 10 guns ; the faces are loopholed for musketry. This Caponier. GEMERSHEI.M. 459 outwork will hold a garrison of 160 men. Each of the flanks E H, E' H', tains six casemates for guns. The ditches of the ravelins are defended by case- mated traverses Q Q', which protect the enceinte in rear. The ditches of tlie countcrguard are defended by casemated batteries X, X'. The casemated bat- teries for mortars ai-e placed at the salients of the polygon in R and R'. (416). At Gcmersbeim the caponier contains either one or two stories of case- Fio. 791. mates for artillery ; at the baliciit a liulc triangular bpaeo ib left open, and gives room for a mortar to throw shells on the approaches. The tracing differs but little from that of Coblentz. The ditch of the ravelin is also defended by case- Fio. 792. mates, and there, as well as in some of the fronts at Coblentz, the re-entering angles are occupied by casemated redoubts, C, C. Reduits arc also formed in 4()0 GERMAN FOKTIFICATION. the salients of the covered way. Gemersheim presents however this difference, tliat the revetments are counterarched and loopholed for musketry. The case- mated mortar batteries are replaced by a pentagonal area left at the salients of the bastions liehiiid the revetment ; the escarp gallery leaves the wall so as to form a courtyard 20 yards by 7, in which five casemates for mortars open. They communicate with the interior of the place by a postern, and ai-e surrounded by a Fio. 793. -t* :^ --^^ 't:rr-- -m loopholed gallery. Right and left of the postern are two powder magazines, the walls of which rise above the rampart and form a hollow traverse, which protects the faces of the bastion against ricochet, whilst in the interior there is room for a battery of three guns. These traverses have a command of 6 feet over the adjoining pai'apets. Similar ti-averses ai-e also constructed near the shoulder-angles, and are ])re- ceded by a ditch forming a coupure. A defensive barrack at the gorge is con- nected with these coupures, or a retrenchment is consti'ucted for the purpose of ulterior defence. In the plan we have traced a countcrsloplng glacis, but at Gemersheim the place is surrounded by a covered way with a rov(!tted counter- scarp, as rejjresented in the pi-ofiie. INGOLDSTADT. Fio. 795. 461 (417). At Ingoklstailt th.- n.iH.niir ;ir. I.cirli. il, and form a kind of citadel: troops can tlins make their exit frum llie place witli rapidity, whilst re-entering places of arms in the covered way further facilitate the sorties. Wc find these casemated batteries for the defence of the ditches of ravelins or counterguards, and hollow traverses at the salient of these outworks to resist ricochet and contain heavy guns to fire on the approaches. What precedes will give a fair idea of the manner in which the principles of Montalcmbert and Carnot have been applied in the recent constructions of Germany, and instead of entering into further descriptions, wo think it more useful to discuss their leading features. (418). The partisans of the bastion tracing have criticised the German system in the following manner: — The gi-eat opening of the angles of the polygonal fortification permits, more readily than with the bastion tracing, the long faces to be directed to those points of the ground on which the enemy will find it difficult to erect his batteries, and in the most recent constructions, as at Kadstadt, (423), the caponier is brought forward so as to increase the opening of the angles formed by the faces ; the ricochet is thereby rendered more difficult. This disposition, together with a greater extent of the fronts, will necessitate a greater 462 GERMAN FORTIFICATION. development of the first and second parallel, but this is not an obstacle likely to delay the progress of the attacks. The besieger will as usual construct his batteries to ricochet the faces of the ravelin, of the counterguards and tbe enceinte, and will even erect in his second parallel a counter-battery to fire across the ditch against the caponier, which a pitching fii-e of heavy guns can easily reach. The hollow traverses constructed on the ramparts ai-e armed with too few guns to hold out long, their masonry must soon give way, but their remblai will continue to form a good protection against ricochet, not such, however, as to liinder it entirely. The besieger will reach the foot of the glacis, and make his third parallel as in ordinary circumstances. Having arrived there, his further advance is no longer checked by the grazing fire of the covered way ; that of the outworks is more plimging and distant, and if the sap can progress before a covered way, it will certainly progress no less rapidly before a countersloping glacis, especially since trench cavaliers can be dispensed with. The defence relies upon the sorties which can bo made with considerable force, but the besieger is aware of it, and as he is superior in number and protected by a parallel, there is every reason to suppose that the engagement will turn to his advantage ; in that case he can pui-sue the defenders to the very gates of the place, and very speedily return to his parallel, whereas he could not follow up his advantage if there were a covered way. At night he may enter the ditch, and watch the preparations made for these sorties. As for the small sorties against the heads of the sap, they will be less practicable also ; and unless the ditch be permanently occupied by detachments, which it cannot be, they must be less frequent ; when retreating they have upwards of 250 yards to run over under no protection, since the case- mates in the ditch cannot fire on both friend and foe ; and when the enceinte is re-inforeed by counterguards, the retreat will be dangerous ; the defenders must pass through the narrow defiles at the extremities of the counterguards which the enemy may occupy, whilst the sortie struggles with the sap, because he is nearer those defiles in some parts of his third parallel : the retreat may thus be cut off". The counterguard once lost, these defiles are easily observed, and futui'e sorties become next to impossible. This is not all, for the harm done to the sap will be more i-apicUy repaired on account of the musketry fire being less troublesome. The sorties would altogether prove too jjreearious a means of defence. More- over, the advocates of this system expect much from the casemated mortar batteries : these will certainly continue firing on the approaches ; now this has always been the case in former sieges, because the mortars may be placed any- where, and the defender invariably places them on the points least exposed to ricochet. There is no reason why they would do more harm tlian in the bastion system ; and the besieger will reach the crest of the glacis very likely sooner than usual, because the little saliency of the ouhvork.s will ]H'rmit him to crown siiiiui- GERMAN FORTIFICATION. 403 tancously the glacis of the ravelin and of the coimtcrguards or bastions. To ]irevciit the crowning, the loopholed wall and the caseniated batteries are not j)roporly organised ; the loopholes, as may bo seen by an inspection of the profiles, are only 10 feet above the bottom of tho ditch, and much below the crest of the glacis ; their fire will therefore be too ascending to prove a serious impediment ; tho same may be said of the caponiers having but one story. At Coblentz the superior stoiy commands a good view of tho crowning ; but its artillery can no more prevent tho crowning than that of tho bastion system, and perhaps it is even less effective for tiiis purpose, as we shall see presently. The little reduits, erected in tho salients of the counterscarp, and destined both to secure access to the galleries of mine and to give reverse fire in the ditches, could not either arrest tho crowning, because their front wall is not flanked, and the besieger can fill their small ditch with fascines or sandbags and destroy them by mines. There is thus good ground to suppose that the glacis will be crowned by tho besieger* and this done, the work of the attack becomes simplified. Engineers who object to the polygonal fortification, are of opinion that the ulte- rior defence will be very slack, because the flanking defences will have been ruined by this time. The caponiers and detiichod walls, as well as the traverses and reduits in the ditch, are in fact as much exposed to tho pitching fire of the batteries of the second parallel, as if there were no glacis or counterguard before them. They base their opinion upon the experiments made at Woolwich, in 1822 and 1824, when a Carnot wall protected by a counterguard, was breached by a battery of eight G8-pounders at 500 yards, and a battery of three 8-inch, and three 10-inch howitzers, at 400 yards. By firing at an elevation of 15° with solid shot, and shells full of powder, a practicable breach was made in six houi-s by 100 rounds from each piece. Next day, 50 rounds rendered the breach perfectly practicable, and on the third day of the experiment the wall was a mass of ruins. It must be said that the firing was rectified, as the effect of each shot was observed and the elevation or charge altered, in actual warfare such could not be the case ; but the possibility of destroying walls at a distance by pitching fire is more or less an established fact; and with a greater or less number of rounds, the walls of the caponiers, &c., must be ultimately destroyed, or at least suffer heavily. Without going so far, we shall suppose that these walls have not been so much injm'od, and see how the besieger would proceed after having crowned the glacis. He will construct counter-batteries against the casemates defending the ditch. Montalem- liert declared that it would be impossible to do so ; but wc do not find in German fortresses that immense superiority pf artillery which he proposed ; the artillery may do harm and somewhat delay the completion of these comiter-batteries, but the experience of past sieges proves that tho flanks of bastions left intact, and e\en rc-intbrcod 1)V retired flanks, could nut prevent the construction of these batteries. \\ 464 GERMAN FORTIFICATION. and the caponiers or casemates even un-injm-ed, do not bring much more to bear on the crowning. Should there be no counterguard, the question of " earth versus masonry," will soon be settled, the caponier must be silenced as it pi-esents too wide a surface, and every shot does it too much harm to admit of a long resistance. The ditches are then dead, and before giving the assault there I'emains only the detached wall to breach, which the counter-batteries themselves can do. If, as at Gemersheim, the enceinte has a regular revetment, the besieger will have no difficulty in destroying the front wall of the pentagonal area, since it is too weak ; the loopholed wall in rear would not resist long either, and a lodgment would thus be easily obtained, from which the miner could blow up the enceinte, and make a regular breach, or breaching batteries might be constructed against the faces. The ravelins, if they had not been abandoned, and the enceinte, could be stormed simultaneously as early as the 15th day of the siege. If the fronts are re-inforced by counterguards, the coimter-batteries of the salient of the glacis, will have to destroy first the casemated batteries or redoubts flanking the ditches of ravelin and counterguard, if this has not been done by the batteries of the second parallel, and also to breach them at their extremities. The lodgments may be made here, as before, without difficulty, since there is no descent of the ditch required, a sap being quite sufficient, and the long ditches, now dead, serve the besieger for the depots, &c. A lodgment on the exterior slope at the salient of the counterguard, can be ti'ansformed into a counter-battery sufficiently strong to overpower the caponier, and to breach the enceinte as before ; or a trench may be run across the terreplein of ravelin for a battery that will breach the curtain ; but the besieger need not do so, as he might be exposed to the casemates that defend the ditch of the caponier ; by breaching the enceinte on the faces, these batteries might be turned and rendered useless, and so much so, that at Gemersheim they have not been constructed, but replaced by three embrasures at a small height above the bottom of the ditch. After breaching the enceinte, the enemy is entirely master of the ditches, and cannot be disturbed, he will be at liberty to turn the interior retrenchment by the mine, or construct in his lodgment on the exterior slope of the enceinte, where he is altogether unseen, some batteries to destroy the defensive barracks, and give the final assault on the 20th day. 1 ^ (419). The name of Prussian system, is now given to a polygonal tracing possessing a decided superiority over the tracing of Fort Alexander. We adopt the same dimensions as are given in military schools. The line of front A A' ^ 450 yards ; the main ditch is 30 yards wide, and its counterscarp is parallel to the enceinte. The ravelin is traced by taking O B ^ OB'=:100 yards, and describing an equilateral triangle BOB': its ditch is 20 yards wide. Casemated batteries for fom- guns flank that ditch ; they arc traced PRUSSIAN SYSTEM. 4(J5 by producing the gorge of ravelin, and taking B M ir 30 yards, and drawing L M = 20 yai-ds parallel to the faces ; the ditch is only 10 yards wide round them. anil in fi'ont where the depth is 5 yards, it is deepened a few feet A revetted counterscarp and a glacis 100 yards wide surround the whole front. The ravelin is divided into three pai-ts. The first C D D', in which C D =r C D' z= 26 yai'ds, is a loopholed wall, and in the terreplein which it encloses, is tlie entrance to the galleries of countermines. The second is limited by the wall E E', erected at distances C E = C E' = 70 yards from the salient. The command of the parapet is greater than in the third part of the ravelin in order to protect it from enfilade, and under the parapet D D', on a level with the terreplein of tlie salient is a battery for 3 mortars. ^ In the third part, there is in front a bastion retrenchment, with perpendiculai- ab — 20 yards, and faces E c = E' , and several other fortresses in Piedmont and Flanders. Jacomo Castriotto, Capt., bom at Urbino, was an engineer of Pope Julius III. He attached himself to the service of Henry II. of France, and sensed under Montmorency, Guise, &c. In his system, the bastions are replaced by round towers, and the enceinte is covered by detached bastions. Vauban borrowed fi-om 494 HISTORY OF FORTIFICATION. He recommended domi-revetments and also him his second and third systems. hollow revetments. Girolamo Maggi, born at Anghiari, was a lawyei'. While judge of the island of Cj7)rus in 1571, he contributed to the defence of Famagosta, then besieged by the Turks. In 1564 he published at Venice, " Fortification of Cities," on the method of Castriotti, with comments of his own. In the system which he proposes the liastions are small, have doul)le flanks, and the curtam is provided with four double flanks. Vauban borrowed from him the curtain of his third system. Girolamo Cataneo in 1574 constructed the first place of arms. Francesco de Marclii, born at Bologna, was engineer of Pope Paul III., for whom he fortified Piacenza in 1547. He afterwards went to the Low Countries in the service of the King of Spain. His work " Military Architecture," pub- lished at Brescia in 1599, contains 161 systems. In them we find the tenaille, ravelin, counterguard, &c., and other outworks and detached works. Subsequent engineers have borrowed from him, and Vauban was at a time accused of having bought up the copies of this work to destroy them, in order to conceal his plagiarism ! Gabriel Busca, who in 1619 published at Milan a work, "Military Archi- tectm-e," is considered by some as the inventor of the great ravelin ; but the German Speckle had already planned it thirty years before, and Busca's system is a mere copy of Speckle's. Floriani, who, in 1630, published at Venice " Defence and Attack of Fortresses," is the first who employed a double covei-ed way. He is considered by many as the inventor of the tenaille of Vauban. Donato lioseUi, in 1678, published at Turin " Inverse Fortification," and pro- posed a system with double flanks not retired, and with a large ravelin with flanks. The shoulder angle of each ravelin is connected by a fausse-braye. The shoulder angles of the bastions and the flanks of ravelin are joined by a wall destined to prevent desertion, and to enable the oflicers to go the rounds : this GKRMAN SCHOOL. Fio. 831). wall is dcstro}X'(l towards tlic latter part of the siege, to enahle the Hanks to defend the ditch. SECTION II.— GEiiMAN School. Altliough the German school dates only from 1815, yet Germany has not been without engineers. They chiefly belong to what is termed the "theoretical school," in opposition to the " practical school," of which Vauban is the head. They jiroposed systems more or less impracticable, and the art did not progress in their hands. (441). Durer (Albert), born at Nnrcmbcrg in 1471, was at the same time a painter, sculptor, engraver, and a civil and military engineer. He died in 1528, one year after the publication of a remarkable work, entitled " Instnictious for the Fortification of Cities, Castles, and Boroughs." (Nuremberg.) He is the first who has written on this subject since the ancients ; and there is no doubt tliat the Germans owe to him the origin of the ideas on whieli tlieir modern method is founded. Ilis fortification consists of a wall, flanked by circular bastions or towers, and a ditch 200 feet wide. The towers are of different tracings. In one project this work is 70 feet high, and eonnnands the enceinte. Artillery is jilaced on the platform, and a casemate for artillery and niusketryallows of giving a grazing fire in the HISTORY OF FORTIFICATION. Fig. 841. ditch. Tlie wall of the enceinte is double : the top is provided with loopholes and covered with a roof. In another project the tower has the same command as the wall, and contains casemates A, A in rear for magazines: the outline of these towers is better calculated to flank the ditch. v w^^^^my/yy/^yi-^/^^itmi'm'^Mi' iir- -[> ZI4V GEHMAK f^ClIOOL. 197 In his project of a fortress formed of a round tower, Diirer has a lr enceinte, with caponiers for tlio defence of the ditcli. ? " 5-i ■•l 1 ::l. I The ■. n.i^u i„ .(....[.h.,, L.-.iher with tlie immense cost of the masonry which his project would necessitate, have prevented their application. (442). Speckle (Daniel), born at Strasburg, in 1536, served at first the Emperor of Germany, IVIaximilian II., as arsenal master ; then the Duke of Bavaria, as military architect. He fortified Ingolstadt, Hagueneau, Ulm, Colmar, and Strasburg, and died just after having published his work " Ai-chitecture of Fortresses." (Strasburg.) Setting aside the Italian system, he proposes several methods. In the first, the bastions are large, with orillons and cavaliers, the flanks arc r-\ triple, and parts of the middle and upper ones aa-e pei-pcndicular to the lines of defence. There are cavaliers on the curtains. The covered way is en cremaillere, HISTORY OF FORTIFICATION. flanked by places of anus. Beyond the glacis there is an advanced ditch. The profiles show the demi-rcvetment, with its fausse-braye serving as a chcmin des rondes. The walls of Speckle have counterforts 5 yards apart, connected at the top by arches, which bear the parapet and render breaching difficult. It is the modern revetment " en decharge." Speckle furthermore proposes the construction of several tiers of arches to resist the fall of the parapet. In his reinforced method the flanks are perpendicular to the lines of defence, and the ravelin is made very salient. Of the value of Speckle as a military engineer, we may judge by the following principles which he advocated in 1589: the greater the number of sides of a polygon the stronger the fortification, because the works will more readily support each other, therefore the straighter the line of fortification is, the sti'onger it will prove ; the Italian bastions are too small ; large bastions are absolutely necessary for a good defence. Cavaliers are needed for each bastion and curtain to impede the progress of the attack, flank the main ditch, and serve as a retrenchment for the garrison ; a great part of the flanks should be perpendicular to the lines of defence; casemated galleries are necessary to give a low fire in the ditcli, and keep oft' the miner of the attack : groat GERMAN SCHOOL. Kici. 850. 499 ravelins increase the strength of fortification ; the covered way is one of the most essential outworks; revetments should not be seen from the country, and the besieger must reach the crest of the glacis in order to breach. All these principles have been duly appreciated by modern engineers. 443). Dillich. He published, in 1640, a Latin work, " Peribologia," or Systems of Fortification. (Frankfort.) Improving the Dutch method, he replaces \ 7 %^ ^ Fio. 852. 500 HISTORY OF FORTIFICATION. the ravelins before the bastion by counterguards, and directs the counterscarp of the main ditch on the slioulder-angles. His ravelin is also an improvement. His low flanks ai-e casemated on the Italian method. In another system, Dillich adopts the tenaille tracing. (444). Rimpler, as military engineer, took part in the defence of Candia, against the Tm-ks (1669). In 1673, he proposed a new system, which he called " Fortification with middle bastions," but gave no drawings. It was only in 1718 that Sturm published a plan of that method. Complaining that his predecessors did not pay sufficient attention to the ground on which the besieger must develop his attack, that the garrison was not well covered, and could not obtain the superiority of fire, he proposed to replace the curtain by a bastion that would flank the collateral works, and be defended by them, to cover the garrison under casemates, and to prepare an interior as well as an exterior defence. UEKMAN SCHOOL. ."Mil In his system, the bastion A is called "bastion of the middle," ab, ab are tiiu faces, ad, ad the second flanks, dc, dc the upper flanks, //, //the middle, and A h the lower flanks. The bastions are jjreceded by fausse-braycs mmm, the salient of which forms a bonnet On the other side of the main ditch, is a double covered way with advanced ditch : the salients arc occupied by ravelins 1 1, and the re-entering angles by interior g'*^, and exterior ^p demilunes. The bastions W I -ppcr Fkink. M;.I,II. Fbnik. /..,.<■,-,■ Fl.,„l;. ;irc rotrcnclied by mt-ans of ditches (punctuated ou the plan) over which wooden bridges charged with earth ai'c thrown : the bastions being breached, the bridge is easily destroyed, and the earth above it serves to throw up a pai-apet. The enceinte is separated from the town by a ditch, and the upper flanks have at their gorge a parapet and defensive casemate for the interior defence. This system has a great importance not only on account of the excellent ideas it contains, but because the principles of Rimpler have been adopted by Monta- lembert and the present Geriniuj engineers. The besieger must carry two ravelins before reaching the counterscarp; then he must attack the fausse-braye, the bastion, its retrenchment, and furthermore drive the defenders from the casemates. The ditches and outworks are powerfully flanked; the retrenchments of the bastions are excellent. On the other hand, the revetments of the escarps are low 502 HISTORY OF FOKTIFICATION. and exposed to escalade ; the advanced ditch pro^•ides the besieger with a lodg- ment ready made, and the angles of defence are rather obtuse. This fortification is not practicable, on accoimt of the gi-eat space it occupies, of the lai-ge gaiTisons it requii'cs, and the immense outlay it would necessitate. (445). G^-iendel d'Ach. — He published in 1677 "New Military Architectui-e'> (Nureniburg), in which he proposed several methods, the most important of which is a combination of the bastion and tenaillc tracings. The enceinte is bastioned and serves as retrenchment : the tenailles arc formed of great ravelins traced on the prolongation of the faces of the bastions. The four flanks of the ravelin and Fig. 859. its reduit, must be destroyed by the mine when the besieger has breached the ravelin. The ditch of the reduit is defended by a double flank constructed on the face of the bastion. Between the tenailles are ravelins with long flanks. The outlay is great, and the place is much exposed to enfilade; but in 1677 ricochet firing was not yet invented. (446). Werthnuller. — Among several works, his " Theatre of Ancient and Modern Maxims of Fortification" was published in 1 69 1 (Frankfort). He proposed corrections to the system of Pagan (464) and offered a tracing en tcuaille. The Fio. 8 GO. A GERMAN SCHOOL. o();^ enceinte has a fausse-braye ; and in rear, the buildings arc disposed for resistance. Tlie long ravelins are flanked by the enceinte ; and their flanks are intended to give a reverse fire in the dead angle of the tenailles. The same remark may be made as before on the ricochet. (447). Sutthiger. — A great partisan of Rimpler, advocates the interior defence and the suppression of the curtain. The figure represents one of the systems he oftered in 1G96, in all of which the ramparts are double. '^iK. ■?s/. (448). Landsberg, horn in 1670, served us an engineer first in Holland, and after 1733 in Saxony: he died a general-major in 1746, having been present at 20 sieges. He published works entitled " New Method of Fortifying Places," and " Fortification of Everybody." (La Haye, 1712.) Although he occasionally proposed improvements for the bastion system, he nevertheless attributed the small resistance offered by fortresses in general to the short flanks which this system unavoidably possesses, and insisted upon adopting a maximum flank, therefore having nothing but flanks, and setting aside the bastion form, he adopted the tenaille. Although Griendel d' Ach and Werth- muller, had before him given a similar trace, yet Landsberg was the first who pointed out its properties. He gave several systems, of which the following affords a fair idea of his principles. It consists of three unrevettod enceintes ; the first of tenailles of 60° a a, with small redans in the re-entering angles, the second b b, of a fixusse-braye wuth bonnets at salient ; the thii'd 9f an envelope c c, of 125 to 225 yards faces replacing the covered way. In tlu; main ditch there are casemated redoubts «i to, for musketry and artillery, as also r r, in the ditch that separates the enceinte fi'om the town. The powder magazines Landsberg proposes to place outside, p p. It is readily seen that the ramparts arc much exposed to enfilade, and yet Lands- HISTOKY OF rOHTIFICATlOX. Fiu. S62. berg has no traverse, as he objects to them, because they give cover to the enemy : the absence of a covered way exposes the place to an attack of vive force ; and as the i-elief is small, escalade may be resorted to ; there is no provisions made for sorties, and the space left for houses is very limited. GERMAN SCHOOL. 505 In another methed recommended for a place exclusively military, the first enceinte is bastioned, and the envelope is replaced by salient ravelins with double Hanks : some fleches thrown up when the front of attack is known, will form an advanced line ; and a retrenchment on Riin]>lcr's princi])les is prepared in the bastions. Landsberg calculates that the outlay will be less tlian for Vauban's hexagon, and that a vigorous defence may bo expected from a garrison of 20,000 men and 60 guns. (449). Voigt. He published in 1713 a " New System of Fortification" (Jena). He adopts the tenaille with casemated redoubts in the re-entering angles : a second enceinte is formed of detached counterguards. In capital of the rcdoubtjs are ravelins and tenailles, the latter of which served Carnot as models (414). The ditclies are made deeper than in Landsbei-g. (450). Sfwm (Leonard Cristophe), boi'n at Altdorf in 1669, was at first pro- fessor of mathematics at Wolfenbuttel, then at Frankfort on Oder. He gained celebrity as an architect, and was attached in that capacity to tlie Duke of Mecklemburg. He died in 1719. He certainly is one of the most productive military authors of Germany. Among his works we may point out his "Com- parison between French, Dutch, and German Military Architecture" (Augs- burg, 1718). He also himself proposed several systems of the bastion and tenaille outline. In the method here represented he has imitated Cajhorii, and coinbincd both tracinjis. 5()() HISTORY OF FORTIFICATION. (451). D'Harsch. He published in 1719, " Dissertations on Military Archi- tecture " (Friburg). The enceinte en tenaille consists of a mere wall, forming a parapet, and covered by counterguards, ravelins, and lunettes. Defensive 'A'- ■^ barracks are consti-ucted on the terreplein of the ravelins. Carnot borrowed from him also. (452). Herlin, a major in the corps of the Pohsh engineers, published, in 1722, "The Complete Works of Rimpley." (Dresden). He proposed an enceinte of detached bastions and ravelins, and divided the town into quarters by double cavaliers erected behind the gorge of the bastions. His ramparts are casemated with a double parapet and n fausse-brayc. GERMAN SCHOOL Fio. 868. /y \h.^/{ ^ (453). Glasser. He published, in 1728, " Ideas on Military Architecture." (Halle). In his reint'orced method, which is considered the best, we find a bastioned enceinte, ravelins with reduits, couiiterguards, envelope and re-entering 508 IIISTOUY OF FOKIIFICATION. places of arms with reduits. The ramparts have a deini-revetment with a chemin des rondes or fausse-braye on the level of the ground. On the capitals of bastions and ravelins are casemated caponiers, which are well covered and powerfully defend the ditches. (454). Herbort was Director of Fortifications in the service of Wui-temborg. In 1734, he published "New Method of Fortification," (Augsburg), in which he proposed two methods. In the first the angles of the polygon are occupied by casemated reduits, surrounded by barracks loopholed for musketry and artillery. These are flanked by two redoubts, and covered by a glacis, before which stands a connterguard. The extremities of these couvre faces form a low flank before the redoubts. Defensive barracks connected by an earthen parapet form a general retrenchment. The ditch is deepened 6 feet before the low flank and the rear of the redoubt, forming an excavation from the counterscarp, of which a grazing fire may sweep the ditch. On the middle of each front are similar casemates with glacis, counterguards, and extra flanks. An envelope of countcrguai-ds flanked by lunettes, which have also their glacis, casemates, extra flanks, &c., surroiuids the whole. This ingenious system has many defects : the outlay is enormous, the unrevetted parapets and the flanks rising in tiers would expose it to an attack of vive force : it would also suffer much from ricochet. The bastion tracing has a great resemblance to this. (455). Avgustua IT., King of Poland (17.'57), proposed several sj'stems, most of which arc so complicated as to be iniprncticable. Tiie following was intended GERMAN SCIIOOI.. 509 for Wittemberg. The gorge of the tenailles is occupied by two parallel defensive barracks, and by caseraated redoubts. Among the several kinds of casemates which he traced, we notice the following, which bears resemblance to the plan of Haxo. (456). Pirscher published in 1771, " A New and Easy Method of Fortification ' (Berlin). His enceinte is cii'cular, and the ditch is occupied by two lines of works ^ n-^ > mutually flanking each other. The covered way and glacis are replaced by advanced works. (457). Vi7-giii was a Swedish general officer. He published, in 1781," Defence 510 HISTORY OF FORTIFICATION. of Fortresses in Equilibrium with the Attack." (Stockholm). This is a remarkable work, and contains the following objections against Vauban's systems, that the breaches cannot be vigorously resisted, that the interior defence is not provided for, that the ravelin is too obliquely flanked, that the fire of the enceinte is too high to sweep the ditch, that the coimterguards are not properly flanked by the ravelin, that the covered way is not calculated for sorties, &c. ; and he proposes several systems more or less complicated, but he does not give profiles. This plan represents his fortification on a square : he is an advocate for stuTounding cities with walls only, and for the construction of small fortresses or citadels exclusively militaiy. The enceinte is bastioned with a triple flank : the low flank a, the middle b, and the upper one c, with terrepleiu respectively 2, 14, and 24 feet above the ground, and parapets 6 feet high. They are at such a distjince apart as not to interfere with the service of artillery, and they not only defend the ditch and over- look the enemy's batteries, but also can direct reverse fire on the lodgment of the bastion of attack, provided its upper flanks have been levelled in time. The bastions are protected against ricochet by a bonnet at the salient as well as by the flanks themselves. The curtain forms a re-entering angle, and serves with the tenaille to give a well directed fire on the outworks. Barracks may be erected at the gorge. The interior defence is adniiralily organized In' means of bastioned towers T, and a donjon A, both of a command equal to that of the bonnets. The towers are casemated and covered with a platform which can receive artillery: they are separated from the donjon by a wet ditch. This donjon consists of a double vault, divided into two stories and surmounted bv a platform from wliich the DUTCH SCHOOL. 511 bastion can be swept. On the outside, the casemates are mounted with guns, destined to fire on the lodgment on tiie bastion, and to defend the passage of tiie ditch ; on the inside the first story is loopholed for nuisketry, and tlio second receives mortars which can fire over the opposite side of the donjon, an invention which Carnot appropriated to himself. As each face of the donjon can direct 24 guns on tlie terreplein of tiie bastion, there will be, including 32 guns from the towers, 56 which the enemy cannot see until he arrives at the salient of the bastion. If we add 10 guns from tlie ujipcr flanks of the collateral salients, and 20 more for which room can easily be found on the terreplein of the curtains not attacked, there will be 86 guns to receive the besieger on the breach, even without the mortars ! As for the outworks, they consist of ravelins, counterguards, tcnaillons, and covered way; of the ravelin with a bonnet at salient and a loopholed gallery under its rampart, flanking powerfully the counterguards with its retired flanks ; the counterguai'ds giving a good fire on the capital of the bastions ; the tenaillons acting as cou\Te face to the counterguards; and of the covered way with a double terreplein receiving additional strength from its lunettes. This covered way, although without traverse, is not much exposed to ricochet, and can offer a serious resistance : the ravelin is too small, and the enemy can simultaneously crown its covered way and that of the counterguaixls. SECTION III.— Dutch School. (458). The Dutch school took its rise in the middle of the sixteenth century, and sprang from the stiniggles of the war of independence. The want of time and money, and the aqueous nature of the soil, led the engineers to adopt fortifications almost entirely made of earth and wood. In this school masonry is rarely employed : the command is small, the number of outworks considerable, especially of hornworks and crownworks, and the defensive character of this fortification is strongly marked. The formulae of the tracings are generally complicated by geometrical constractions. The chief engineers were: — (459). Freytaff, who published " New and Enlai-gcd Military Architecture." 1630 (Leyden). In his method he fixes the maximum of the angles of bastions at 90°. The flanks are perpendicular to the curtain, and the whole enceinte is surrounded by a fausse-braye on' a level with the ground. The salients of bastions are covered by lunettes, and the curtains by ravelins. The escarps have no revetment. The chief defence of this fortification rests on the wet ditches, which, liowevcr, would tail in frosty weatlier. The ravelins arc too small to cover HISTORY OF FOHTIFICATION. Fig. 876. even the curtain, and the hmettes, when taken, afford an advantageous lodgment for the enemy. Marolais (Samuel), who in 1627 published "Military Architecture "(Amster- dam), and also adopted the fausse-braye : the flanks were retired and casemated. Fig. 877. Volker (1666) proposed a larger ravelin, triple flanks and the fausse-braye. Melder (1670) gave a tracing that differs from that of Freytag, by the absence of ravelins on the salients of bastions. Russemtein (1670) followed Pagan (464) with this difference, that his bastions are simple. He gave a revetment to the escarps. DUTCH SCHOOL. ol3 Scheiter (1672) published " The Newest Military Practice " (Bnmswick): he borrows from Castriotto the detached bastions, gives to them a faussc-braye, as well as to the enceinte, and surrounds his place by a double covered way. Among his proposals, we may notice his counterguards, which consist of two walls 18 feet thick, 50 feet apart, witli a roof of timber and earth ; the interior space is divided by a floor into two stories, affording room for two tiers of guns. Neuhauer (1671) gave to the re-entering places of arms a reduit that was imitated by Corniontaingne, and proposed six fold flanks. Heideman (1673) imitated Speckles. . Heer (1689), with his twelve systems, came next, and after him Ccehorn, who is called the head of the modern Dutch school, as Frcytag and Marolais were called the head of the old. (460). Ccehorn (Miuno Bai-on) was born at Leeuwarden in 1641. lie served with distinction in the wars of 1672-76, and rose to the rank of Lieuteuant- General. He defended Namur against Vauban in 1672, and conducted several sieges during the wai's of the league of Augsburg, and of the Spanish succession. He was also an excellent general officer, and forced the French lines between the Scheldt and the sea in 1 703. He died in 1 704. His principal woi-k is " New Forti- fication." (Leeuwai'den, 1702). His method of attack was the veiy opposite of that of his contemporary and rival Vauban ; whilst the French engineer advanced surely and slowly, sparing life and intrenching every step, Ccehorn sacrificed every- thing to time, and trusted to an overwhelming fire of artillery and audacious assaults. It is thus that at Bonn, in 1703, besides a large park of heavy ordnance, he employed 500 small mortars to throw grenades. We may here say a few words on the method he employed in fortifying a height that commands Groninguen. It is entirely different from his three systems (fig. 880), and consists of independent works so combined, that the loss of one of them does not entail the fall of the rest On the outside the works present them- selves as tenailles, whose wet ditches are flanked by double traverses, which are L L IIISTOKY OF FORTIFICATION. themselves insulated by the ditch. On the inside, the gorge of each tenaille is closed by a bastioned front with a weak parapet, so as to be easily destroyed from the place, should the enemy become master of a tenaille. Tlie escarps and counter- scarps are revetted, and a covered way surrounds the whole. SECTION IV.— FnENCH School. (461). The first engineer who began to modify the fortifications in France was a Spaniard, Peter de Navarre. Ho had served in the Spanish army against the Moors and against the French, had been made prisoner by the latter at the battle of Ravenna, 1512, and afterwards entered their service. He was the first to intro- duce mines and countermines. He breached the castles of Nuovo and Del Ovo at Naples, in 1503, by mining. Contemporaiy with Peter were the two distin- guished engineers Mkadel and La Fontaine, but none of them left any work. The Italian system was adopted, and Catherine of Medicis invited several Italian engineers into the French service ; among them, Adam de Crapone, Campi, Bellarmato, Bephano, Castriotto d'Urhin, &c., by whom Landricies, Philippevillc, Thionville, Metz, &c., M'ere fortified. Beroil de la Treille is the first French author on Fortification, but he followed the Italian principles : his work, " Manierc de fortifier les Villes et Chateaux," was published in 1557 at Lyons. (462). Errard de Bar-le-Dnc is considered as the head of the French school. He published in 1594 " Fortification d^montre et reduite en Art;" he constructed the citadels of Amiens and Verdun, and also fortified Montauban, Sedan, &c. ; he belonged to the corps of military engineers formed by Sully in 1602. He is the first who fixed, at 60°, the minimum of the salient angles, who adopted 290 yards as the maximum of the line of defence, and who fortified on the exterior polygon. His system, however, is inferior to the Italian. He had for a rival FRENCH SCHOOL. FlO. 881. Cliuule Cliatillon, wlio, for tlio first time, employed the sokliers instead of liired labourers, to work in the trenches. (463). Antoine Deville (Le Chevalier), born at Toulouse, 1596, died a general 1657, published in 1628 (Lyon) " Les Fortifications du Chevalier Antoine Deville;" and in 1639, "De la Chai-ge des Gouverneurs des Places," a work highly commended by Carnot He is the first who wrote on mines. He fortified Calais, Moiitreuil, &e. His system is a mere modification of the Italian front. (464). Pagan (Comte de, Blaise Frangois), born at Avignon, 1604, entered the army when twelve years old, served with distinction, and became general in 1642. Although having lost his sight, he devoted himself to the study of Fortification and Mathematics till his death in 1665. Besides several works on Asti-onomy, ho published (1645) "Les Fortifications de M. le Comto de Pagan," Par-is. Pagan gi-eatly improved the art, and paved the way for Vauban. He adopts three kinds of Fortification, the gi'eat, the mean, and the small ; in the first the front = 390 yards ; in the second, 350 yards ; and in the third, 312 yards. He was the first to employ the perpendicular, which he equals to 58 yards, to draw the line of defence. The faces of the bastion m -rV of the front. The flanks are perpendicular to tlie lines of defence. The ditch is 30 yards L L 2 516 HISTORY OF FORTIFICATION. wide at salient, and its counterscarp is directed on the shoulder angle of the bastion. Inside each bastion he constructs an interior retrenchment, its magistral being parallel, and 32 yards from the enceinte. The flunk is triple ; the first is retired and on a level with the ground, the third is on a level with the inner bastion, the second has an intermediary command. The ravelin has a 90 yards' face, and occasionally receives a reduit. A counterguard sometimes covers the bastions. In another method, called " re-inforced," the enceinte is preceded by a continuous envelope. Fig. 884. Despite the many advantages which the Fortification of Pagan possesses over tliat of his predecessors, it contains several defects, among which we may mention the possibility of breaching the curtain from the ro-eiitering place of arms, thereby turning the interior bastion. The triple (lanks are also defective, the defenders being too much exposed to the splinters of the upper scarps. (465). Vauban (Sebastien le Pretre de), born at Saint Leger, 1633, entered the service in 1650, became general in 1688, and died Marechal de France, 1707. FRENCH SCIIOUL. 517 He is the best engineer that France boasts of. He never wrote on liis method. He fortified thirty-three places, and improved upwards of 300, and his successors, in comparing his works, have, for the sake of simplicity, classified them into three systems. He conducted fifty-throe sieges, and never defended a single fortress ; and so greatly did he improve the moans of attiick, that the defence has ever since been unequal to it. In 1673, at the siege of Maestricht ho invented the parallels; in 1683, at the siege of Luxemburg the trench cavaliers; in 1697, at the siege of Ath, the ricochet fire. He left twelve volumes manuscript (a few only have been published) " Mes oisivetes." The volumes 8 and 9 treat of the Attack and Defence of fortresses. Among the fortresses which ho constructed we may name Dunkirk, the citadels of Lille, Ath, and Charleroi ; Maubeuge, Saarlouis, Phalsburg, Longwy, the citadel ofStrasburg, Toul, &c.j&c. (466). Allain-Manesson Mallet (1630-1706), wds horn ai Favis. He served as iniHtar}- engineer in the Portuguese army under Marechai Schombcrg. In 1671 he published " TravaiLx de Mars" or " now fortification," the first valuable work written on the subject. In 1667, he fortified the castles of Aronche and Fereirc. (467). Blondel, Fran9ois (1617-1686), was born at Ribemont. After having travelled in Germany, Italy, &c., and performed diplom.atic missions in Egyjit and Turkey, he became famous as an architect. In 1683, he published (Paris), " Nouvelle mani^re de fortifier Ics Places," and Lewis XIV. rewarded him with the honoraiy title of Marechai de Camp. Fio SS.">. In his system, the bastions are large and acute : their flanks are long and triple. The bastions are covered by counterguards, whose ditches, like those of tiie ravelins, are defended by law liatteries. Small ravelins are substituted for tlie rcduit of the re-entering place of arms. It is weak in outline, and yet costly in masonry. (468). Bernard.— In 1689, he published (Amsterdam), " La nouvelle manicre fie fortifier les Places." He proposes a double enceinte covered by counterguards 518 HISTORY OF FORTIFICATION. and ravelins having high and low faces. The outer bastions can be isolated, after the enemy has opened a breach, by blowing np the flanks. He gave two other methods, which are also based upon good principles. (469). Saint Remy. — The enceinte is composed of isolated forts well covered by ravelms, counterguards and lunettes. Each fort contains a barrack for the garrison. The capital defect of this system is, that the loss of one fort deprives the collateral ones of flanking defence on half their perimeter. (470). Eosard, at first in the French engineers, became Director of Fortifications in Bavaria. In 1731, he publislicd (Nuremberg), "Nouvelle Fortification Fran^aise." In his system, which would be good if the enceinte were not exposed l-'RKNCH fSCllOOL. to bo breached from tlio covered way of the ravelin, tlie liastions and ravelins are retrenclu'il : tlio flanks are formed of good casemates, which secure the defence of £CtC the main ditch. The tenaillons and counterguards, however, do not sufficiently cover the bastion and ravelin ; the first covered way has retrenched places of arms: the second is defended by lunettes, which communicate with the place I)y means of galleries. (471). Cormontaingne is supposed to have been born in 1692. In 1716, he entered the coi-jis of engineers, and soon acquired an European celebrity by numerous publications on Fortification, in wliich he corrected the methods of Vauban. In 1728, he constructed at ]SIetz the crown-work of Fort Moselle, and ill 1733 that of Bellecroix, in which are found most of the improvements he pro- posed. In 1734, he distinguished himself at the sieges of Traerbach and Philipsburg; in 1738, he constructed the crown of Yutz at Thionville ; in 1744, was at the sieges of Tournai, Fribourg, Menin, Ypres, »S:c. He died in 1752 a general. He left several memoirs, which were published long after his death, under the title " Memorial pour la fortification, I'attaque et la defence des Places," (Paris, 1809.) A more complete edition was published in 1835. (472). Belidor, Bernard Forest de, (1697-1761,) was born in Catalonia of French parent.s. He served in the corps of engineers during several campaigns, 520 HISTORY OF FORTIFICATION. and then became professor at the school of artillery at La F^re, and general insjicctor of sappers. He invented the globes of compression, which were tried for the first time at Bizi, in 1753. He is the author of several works. Among them we may mention " La Science des Ingenieurs, 1749; Architecture hycb-aulique, 1750." He proposed several systems, but only gave diawings. The following resembles Rosard's method, but is not so good : a first enceinte consists of small bastions ; a second of large bastions with retrenchments > a third of outworks. Fig. 890. '-2'J political principles, he retired into private lif'o, having strongly opposed the creation of the Empire. In 1814 he accepted service, and was entrusted with the defence of Antwerp. At his return from Elba Napoleon made him Minister ; banished at tlie Restoration, he retired to Ccrnay, then to Warsaw, and lastly to Madgcburg, where he died in 1823. lie left several works: the most celebrated is " De la Defense des Places Fortes," 1810, which he wrote at the request of Napoleon. (487). Noizet, a general in the corps of Engineers, is now living. While Professor of Fortification at the school of Metz (French Woolwich) he corrected the system of Cormontaingno, and offered a tracing which has been adopted in France as "■the modern system." In 1860, he published an excellent work, " Principes de Foi-tification." (Paris). (488). Dufour, a general in the service of Switzerland, is now living. He served at first as an officer in the French corps of Engineers. In 1847, he commanded the federal forces. lie has written several works, among them " De la Fortifica- tion permanentc," (Geneva, 1822), in which he proposes a new system, which is preferred by many to that of Noizet. (489). Choumara, a colonel in the corps of Engineers, is now living. He established his reputation in 1827 by the publication of his " Memoires sur la Fortification," whilst yet a captain. Meeting with jealousy at the hands of his superiors, he felt so discouraged that twice he retired from the service. He has rendered great services to his country: and of his inventions, the barrack kitchens (foumeaux economiques) merit special notice, for these kitchens save upwards of fifty per cent, of the fuel hitherto consumed by the army. (490). Haxo (Francois Nicolas Benoit, Baron) born at Luneville in 1774, died at Pai-is ill 1838. Served under Chasseloup in Italy, and afterwards at the sieges of Saragossa, Lerida, and at the battle of Wagram. He conducted the sieges of Mequinenza and Tarragona, made the campaign of 1812, as aide-de-camp to Napoleon, became lieutenant-general in 1813, and fought at Waterloo. Under the Restoration, he was ap[)ointed President of the Committee of Fortification, and fortified Bclfort, Sedan, Grenoble, and I'Ecluse. Under Louis Philippe, ho conducted the siege of Antwerp. As we have said, Haxo did not j'ublish any thing, and there is no fortress built exclusively on liis system. His casemates are to be found, however, at Grenoble, and at Lyons in the forts Loyasse and Saintc Foy. GENEKAL INDEX. PAGK. PAGE. Abattis .... 121, 164, 188 Augustus 508 Accessory Defences . . 106 Advanced AVorks 361 Covered Way 365 Ditch . . 365 Balks 192 Lunettes 361 Banquette 33 Alderson Platform 113 Barbettes 106 Alexander Fort 457 Construction of 108 Aniericau Embrasure . 3'J9 Barrage . . 408 Ammunition for Men 23 Barricades 1 62, 166 Field ArtiUery 6 Barriers 154 for a Fortress 256 Bastion 81 for a Siege 260 — — • Tower 298 Coast Defence 375 Detached . 298 Wagon 7 • Empty 215 Angle of Defence 39 . Full 215 of Ciirtaui 82 Flat 215 Diminished 82 Invention of 490 Dead 40 Lines 93 of Elevation 24 Bastioned System Flanked 82 Principal 413 of Flank 82 Defects of 437 of Polygons 211 Forts 81 Ke-entering •38 Fronts 104 Salient . 38 Bastionet 367 of Shoulder 74,82 Batardcau 217 Undefended 38 Sluiced 409 Approaches 232 Batteries, Field 5 iVrmament 255 Horse . 5 Armstrong Gun 19 Mountain 6 Artificial Fortification 30 Ricochet 229 ArtiUery _ . 1 Breaching 242 Organization of 5 Cavalier . 229 Carriages 6 Elevated . 230 Field 5 Siuiken 230 Siege 259 Half Sunken 230 Coast 375 Haxo 401 Fortress 255 Blinded . 251 Assault 246 Battering Train . 259 Attack of Field Work 185 Bay . . 194 a Fortress 219 Beds 10 by Surprise 219 Belidor 519 Selection of the Point of 223 BeUows 272 of Vauban's 1st System 219 Berm 35 2nd and 3rd System 300 Bernard 517 of Modem System 312 Beroil 514 of Coehorn .329 Besieging Force 257 by the Mine 286" BickfordV Fuze 16 GENERAL INDEX. PAGE. Blanshard Pontoons . Casks, Contents of . . . Blasting .' 277 Castles, Deience of . Blmdale .... 244, 250 Castriotto Blinded Sap . 237 Cataneo . Battery . 261 Cavalier .' 3C Descent . 244 Curtain Blockade . 221 Retrenchment Blockhouse 85 of Trenches Blondel . 517 ■ Batteries Boat Bridge . 195 Cavalli's Gun Body of the Place . 213 Centrobarique Method Bomarsund . 378 Chamber of Mine Bombardment . . 221 of Ordnance Bonnet . 130 Charge of Guns Bonnet-de-Pretre 75,100 of Mines . Boom .... . 208 Chase Booming out . 103 Chasse Bore .... 2 Chasseloup-Laubat Bored iip Guns 5 System of Bousmard 528 Cheeks . System of . 413 Chemin des rondes Boxer's Shells 12 Ches.ses Fuzes 16 Chevaux de Frise 1 Boyaux . 232 Choker Branches . 262, 267 Choumara . Breach, Assaidt of . 246 Principles of Defence of . 252 Churches Breaching . 243 Circular Portions Breastwork 37, 162 Fortification of Muntal enibcrt Breech 2 Redoubts Bridges, Military . 191 CircumvaUation Bridge Head 76, 207 Citadel Buddings, Defence of . 174 Coast Defences Blinded . 250 Batteries Bullets 22 Coblcntz .... Bulwarks . 489 Ca?horn Buoyancy . 205 First System Busca .... . 494 Second System . Third System Attack of Calibre .... 2 Jlortar Camoiiflet .... . 277 Cologne Canister .... 11 Command . . Capital .... 38 of Fii-e . Capitals, Fortification of . 484 of Ob.servation Caponier 115, 442 from Conditions Double . 212 Communications in Field-works Carabine-a-Tige 22 in Permanent Works Carcasses 13 Galleries of . . . . Carnot .... . 528 Comparison, Scale of Bastioned System . 449 Concave Flank . Second System . 453 Concussion Fuze Tliird Sys"tem 455 Congreve Rocket Carpi .... . 493 Conjunct Muies Carronades . 1, 3 Continued Lines Cascable 1 Contra vallation i Case .... . 268 Cordages Casemates 293, 400 Cordon Haxo . 401 Cormontaingne Platform 10 System of Caseniatcd Retrenchment . 341 Counter-approaches Cask Bridge J 96 Couuterarched Revetn cuts (JENEUAL INDEX. Coiuiter-battery . I>.\GE. 229, 242 Detached Bastions I'AfiE. . 295 ( uunterforts 217, 347 Works . . . . . 366 — — Dovetailed . 347 DeVille . . . . . 515 IJectangular . 347 D'Harsch .... 506 olVauban 217, 347 Diagonal Scales 46 Coiintergiiards . 354 Dillich .... . 499 Coiuitermincs . 278 Dimensions of Ordnance 17 System of . 279 Direct Fire 27 Counterscarp 34 Directing Plan 223 Gallery of IIG. 279 Dispart 2 CoiuitersloiAng Glacis . 451 Ditch 34, 351 Revetment . 347 Advanced . 365 Coupures 30G, 363 Passage of a Dry 244 Covered Way . 36, 292 Passage of a Wet . 245 Properties of 292, 359 Defence of . . . 115 Advanced . 365 of Bastioned Fronts . 83 Crater . 276 Division of Labour 145 Cremaillere 91 Double Redan 75 Crest, Superior . 34 Drawbridges ■ 389 Interior 34 Old 390 Exterior . 34 Bascule . 391 Cross Fire 28 of Dobcnheim . 391 Crochets . 213 Jersey . 392 Crownwork 76, 359, 365 Belidor . 392 Crownitig of Covered Way ' . 240 Poncelet . . 393 Crow's Feet 122, 188 for Field Works 155 Cugnot . 526 Dufour .... . 529 Cnnette 309, 351 System of 419 Curtain 82 Countermines of . 279 Length of 104, 335 Tower of . . 400 Dundas Gims 5 Duvivier .... . 483 Dam .... 125, 410 Diner .... . 495 Dead Angle 40 Dutch School . 511 Deblai ... 35, 131 Dwarf Traversing Platform 9 Defence of Field Works . 189 a Fortress . 248 -^ — of Frontiers . 481 Echarpe, feu d' 27 Houses 174 Elevation . . . 53 HcdL'os . 166 of Guns 25 Walls 171 Embrasures through Parapets 109 Defilade . 127 through Masonry . 398 of Open AVorks 128, 143 Tracing of . . 109 of Enclosed Works . 129, 144 American . 399 by the Plane of Site . 143 Enceinte .... . 213 by the Plane of Defilade . 143 Enfield Rifie by Sinking the Terrcplcin . 143 Enfilade .... 27 of Permanent Works . 382 Entanglement . 122 Defilading . 143 Envelope .... . 357 Defiles .... . 182 Envelope Gallery . 280 Dclvigne Bullet 22 Epaulement . 109, 2.30 Demi-bastioned Fort 85 Errard .... . 514 Demigorge 82 Escalade .... . 220 Deniihme 212,291,352 Escarp .... 34 Demi-parallel . 234 Gallery of . 279 Demi -revetment . . ^ . 344 Esplanade . 372 Demolitions 287 Expence Magazine . 231 Depots .... . 227 Exterior Crest . 34 Depth of Ditch 35, 351 Descent of Ditch . 244 Destruction of Obstacles . 187 l.\-.ces of Works . 40 of WaUs . 286 Faluis . .-.24 V -ing Bridjje Focus of ignition of explosion Foisonnement Fords Forts Fortification Natui-al and Artificial Rasant and Fichant Regular and Irregular Perpendicular Polygonal . German Fougasse . SheU . Stone Foundations Fowke's Pontoons Fraises Frames Francis' Pontoons French School . Freytag Front Limits of Bastionod of Counterguard; Frontiers . Fuzes ^l/ux'^^-^'^^yC i2^UA^ GENERAL INDEX. ^ ^yVO^A/ M\rv •)(•- PAGE. 179 148 342 204 74 215 365 198 407 494 202 275 276 132 204 81 30 30 3? 209 437 442 457 123 124 124 350 195 120, 188 2G3 195 514 511 81 104 356 481 Gabionade Gabions . 241 149, 225 PAGE. Gads 149, 225 Gallery of Counterscarp 116, 279 • of Communication . 280 of Escarp . . 282 of Descent . 244 of Envelope . 279 Reverse 116,366 Small 262, 271 Inclined . . 266 Destruction of . 287 Garrison of Field Works 101 of Fortresses 256 Garrison Standing Carriage 8 Gateways (Temersheim 388 459 GenouillSre 109 German School . 495 Fortresses . 468 Systems . 457 Gillot 286 Glacis 35,2 92, 360 Countersloping . 451 — Coup^ . . 360 Glasser . 507 Globe of Compression 277 Gomer Chamber 2 Gorge 74 of Bastion . 82 Gosport 368 Grape Shot 11 Grenades . '. 13 Grreudel d'Ach . 502 Ground, Influence of . 98 Ground Light . 13 Gromid Line . 53 Grummet 15 Guard of Trenches . 227 Guerite 298 Gumpertz, Countermines of 278 Gunnery . 23 Guns 1,2 Gun Carriages . 6 Rifled 18 Gunwale . 192 Haxo 529 Casemate . ... 401 System of 433 Hay's, Colonel, Bullet ... 22 Hedges 166 Heideman ...... 513 Heilingen-Kreutz . . . .476 Herbert 508 Herlin 506 Herses ...... 388 Hurter 112 Hollow Shot 11 Hornwork ... 76, 357, 365 Horse AitQlery 5 Horses 10 Hot Shot 375 GENERAL INDEX. I'AGE. 1 PAGE. Houses 174 1 Lines of Redans . . . . 89 Defence of . 177 ofTenailles . . . . 88 Howitzer 1,4 Indented . . . . 91 Embrasure for 110 With Intervals . . . . 93 Carriage 8 Lintz .... 477 UurcUes .... 151 Listening Galleries . . . . 280 Lock Traverses . . . . 237 Lodgment 247 Ice, Passage on 205 Loopholes .394 Indented Lines . 91 Revolving 397 Independent Scarp Wall . 349 Lunette 74 Inferior Crest . 34 Advanced .... 361 Inriucnce of New Weapons 487 of Ar9on .... 363 Iii,-..Ulstadt 461 hitnuched Camps 372 IntiitKbment 37 Machicoulis . . . . 1 79, 366 Inuiulations 24, 406 Madras Platform 113 of Permanent AVork 406 Magazines ... 2 i\, 403 Time to ALake . 126 Maggl 494 Invention of Bastions 490 Magi.stral Line .... 65 Investment 222 Gallery .... 279 Iron Gabion 150 Manesson Mallet 517 Isolated Fieldworks . 74 Mantlet .... 23G Isomctrical Projection 65 Maritime Frontiers . 434 ItaUan School . 490 Marchi 494 System 491 Marolais .... 512 Marquois Scales 48 Martello Tower 375 Jacob's Bullet 23 Material, Strength of 206 Jebb's Double Sap .... 237 Maximilian Tower 477 JouiTial of Siege . . . .253 Maximum and Minimum of Redoubts 102 Junk 15 Starfort .... 103 Bastioned Fronts 104 Jlayence .... Melder 476 Keep 96, 183 512 Merlon 112 Military Bridges 191 Labour 145, 160 Pits 123 La Chiche . . 523 MiU 181 Ladder Bridge 202 Millar's Guns 5 Scaling 220 Mines 262 Lancaster Guns 18 Charge of ... . 276 Rifle 23 Tamping . 275 Landau 295 Firing .... Attack by ... . 275 Landsberg 503 . 285 Leaning Revetment 345 Mini^ Bullet .... 22 Lebrun, Coimtermines of 278 Modern System . 304 Leopold Fort 472 — — Attack of . 312 Lever Bridge . 201 Moment, Place du . . . 101 Light Balls 13 Moments .... . 412 Limber . 6 Monk's Guns 5 Line of Defence 39 Montalembert .... . 526 Length of . 40 Systems of ... Tower .... . 437 Line of Least Resistance . 276 . 447 Line of Metal . 23 Mooring . 194 of Metal Elevation 24 Mortars .... ■ 1,4 of Fire 24,34 Bed.s .... 10 of Sight . 24 Platform .... . 112 Lines of Bastions 93 Muzzle 1 of Circumvallation 87, 223 of Contravallation 87, 223 Continued 87 Napoleon's Gun.s IB GENERAL INDEX. Naval Carriages liheU Neubauer . New Brissacli Noizet System of Obstacles . Organization of Artillery Opening of the Trenches Ordnance — - Table of . Orgues Orillons of Vauban of Coehorn Outline Outworlis Overcliarged Mines Paccioto d'Urbin Pagan System of Pail Palisades . Parados Parallels . First Second Third Fourth Parapet Thickness of Park of Artillery Engineers Pas de Souris Passage of Dry Ditch AVet Ditch Rivers Penetration of Projectili Percussion Fuze Perpendicular Petard Pickets Piers of Casks . Pile Bridge Pirscher Pits Pitching Fire Place of Arms Place du Moment Plan Plane of Defilade of Fire of Mines of Site Platforms, Common Alderson . Madras Mortar Traversing Plongee Point Blank PAGE. 10 12 513 296 629 418 213, 292, Polygon Angle of . Interior Exterior . Polygonal Fortification Pontoons Pontoon Bridge Portfire Position, Guns of Postern Powder Hose Powder Magazines Pei-manent Preponderance Pritchet Bullet Profile Profiling Projectiles . Projections Isometrical Prolongation of Faces Protractor . Prussian System Quarter Sight Queue d'Hironde Quick Match Quill Tube . Friction Tube Rack-stick and Lashings Radius of Crater Explosion Rupture Raft . Raft-bridge Ramp Rampart Randing Range of Artillery Armstrong — — Whitworth Radstadt Ravelin Reamed out Guns Reconnoissance . Redan Double Lines Redoubts . Circular Garrison of Tracing of Reduit of Field-works of Ravelin Places of Arms Recntermg Angle Place of Arms Reinforce . Relief. 211 334 334 442 191 192 16 6 386 276 231 403 2 23 62 144 10 52 65 225 50 464 276 276 193 197 107, 216, 387 34, 489 . 149 25 21 21 471 212,291,352 5 174, 182, 223 74, 100 75, 100 87 76 96 102 . 141 96, 183 305, 353 305, 360 38 . 213 36, 335 GENERAL INDEX. 537 Kemblai Retirade Retired Flank . Retrenchment in Bas Reveroni Reverse Fire of Orillon . Revetments of Sods of Fascines of (Jabions of Sandbaijs of Flanks of Hurdles Full . Demi . Leaning Sloping Rectangular Hollow Rhana Ricochet Fire liatteries Rirted Ordnance Ririe pits . Rimpler Roads Rocket, Signal Congreve Tube . Robillard . Rogniat Rope Bridge Rosard Rosetti Rottberg . Royal Mortar Places Russenstein Saddles .... Salient Angle Places of Arms . . . 213, SaUv-ports St. Remy San Miciieli Sandbag Sap .... Double Flying Jebb's Serpentine . Blinded Standing Faggot Roller Sarrelouis Saxe, Marechal de . ^ Scaling Ladders Scales .... Scarping .... Section .... IWOE. PAGE. 5, 1.J1 Selection of an Outline ... 98 118 Schcitcr . 513 302 Sh.irt 264. 269 337 Shell Gmi 3 627 Shells 11 27 Common 11 302 Mortar 12 150 Shrapnel 12 148 Diaphragm 12 149 Fougasse 121 150 Shell Fuze 10 151 Guns 3 151 Shoreham Battery . 379 344 Shot . 10 344 Canister 11 345 Grape Hollow 11 345 11 345 Shot Guns 2 347 Shoulder Angle 74, 82 525 Shrapnels 12 28 Siege : 222 229 Carriages 7 18 Signal Rocket 14 123 Slant Fire 27 500 Slope, Measure of 33 166 Superior 33 14 Exterior 33 14 Interior 33 15 of Banqette 33 521 of Rampart 34 483 of Ramps 107, 216, 387 199 Slow Match 16 518 Slueing 149 494 Sluices . . . 406 520 Smoke Balls 13 4 Sods . 150 332 Sole _ 109 512 Spanish System Speckle . Specific Gravities 492 . 497 . 205 192 Splinter-proof Travers . . 231 38 Staircases 216, 387 , 360 Standing Sap . 235 , 292 Starforts 77, 100 518 Tracing of . 141 493 Stockade 117, 120 151 Stone Fougasse . 124 234 Stores . 257 236 Strength of Garrison . 256 233 in Field-works 101 237 of Material . 206 237 Sturm . 505 238 Subcrest . 58 235 Subterranean Warfare . 285 225 Superior Crest 34 , 234 Surcharged Mines 276 303 Surprise 187, 219 522 Suttinger . . 503 220 System of Fortification . 209 42 of Vauban, First >10, 289, 301 158 „ Second . 293 61 — ,, Third . 294 538 GENERAL INDEX. System, Modem , Cormontaingne Coehom Bousmard . Chasseloup Noizet Dufour Haxo PAGE. 304 309 315 413 416 418 419 432 Table of Ordnance of Penetrations of Range of Specific Gravit Tambour . Tamping . . Tangent Scale . TartagUa TcnaiUe . Head Lines Tracing . Tenaillons Terreplein Tete-de-pont Time of Execution Time Fuze Tower Bastion . Martello of Lintz . Dufour Montalembert Verona Trace Tracing on Condition Trail Trajectory Traveller . Traverses Splinter-proof Trench Cavalier Trenches . Trestle Bridge . Trincano Troupe of Ravelin 75, 17 26 25 . 205 . 121 . 275 24 . 493 211, 291, 354 75 '. 437 . 357 33 76, 207 147, 159 16 . 293 . 375 . 477 . 400 447 . 479 37 . 336 . 203 24 . 203 . 154, 213 . 231 . 241 159, 227 . 198 . 526 . 292 Troupe of Tenaille Trous-de-loup Trucks Trunnions Tubes PAGE. 291 123 274 2 15 Vauban Vauban's Lines Verona 468 Towers 479 Ventilation 272 Vertical Fire 28 Villages 182 Virgin 509 Voigt 505 Volker 512 Wads .... 15 Wahrendorff Gun 18 Waling .... . 149 WaUs, Defence of 171 Destruction of . . 286 Water in Ditches . 290 in Permanent Works . . 405 ■ in Field Works . . 126 Weight of Guns 17, 205 ^ of Men 205 of Material . 205 Weir 125, 410 Werthmuller . 502 Width of Ditch . 35 Wilkinson Bullet 23 Windage .... 2 Whitworth Gun 21 Woods .... . 182 Zig-zags 232 Zone of Defence .... 88 MITCHELI,, PRINTER, 39, CHARINO CROSS. °/3 d Berkeley CDsqaa3M7i