bastion, being from 8 to 12 feet above the rampart, with a parapet 6 feet high. Its use is to command some rising ground within cannonshot, and to serve as a traverse for preventing the neighbouring cur→ tains from being enfiladed. Parallels, or Places of arms, thrown up at sieges, are trenches formed to connect together the several approaches to a besieged place. Zig-zags, or Boyeaux of communication, are trenches made for the approaches from the parallels to the besieged place. They are generally 3 feet deep, and have a parapet, and banquette. A Redan consists of two faces forming a salient angle (which should not be less than 60°) with parapet, &c.* A Lunette has two faces, similar to the redan, and also two flanks.* A Redoubt is a square, polygonal, or circular field fort.* A Star fort consists of a succession of salient, and re-entering angles, formed on the sides of a polygon. These forts are usually constructed on a triangle (when they have six salient points), or a square (having eight salient points).* Têtes de pont, or Bridge heads, consist of redans, &c., which are constructed upon the banks of rivers, to protect the passage across them.* Lines are formed for the entrenchment of armies, and are composed of a succession of redans, &c., joined by curtains, which should not be more than 120 yards distant from each other, to afford mutual protection, and defence.* An Epaulment is an elevation of earth thrown up to cover troops from a flanking fire. Loop-holes are oblong holes, from 15 to 18 inches long, 6 inches wide within, and 2 or 3. without. They are cut through timber, or masonry, for the services of small arms. Palisades are stakes of strong wood, 8 or 9 feet long, and 6 inches thick, fixed about 3 feet in the ground, and 3 or 4 inches asunder. Fraises are a kind of palisades, placed horizontally, or obliquely in the exterior slope of ramparts. Chevaux de frise consist of a piece of timber from 9 to 12 feet long, and about six inches in diameter, into which staves are inserted crossways, about 9 inches asunder, about 2 inches thick, 6 feet long, and pointed at the end, if not shod with iron. Their use is to stop up a breach, defend a passage, or form an entrenchment against cavalry. Chevaux de frise are sometimes made entirely of iron. Abattis consist of trees with their branches shortened, and sharpened at the ends: they are used instead of chevaux de frise on an emergency. Hurdles are about 3 feet high, and 2 broad, and are used in sieges to stop up breaches, &c. Trouz de loup are holes dug in the ground in the form of an inverted cone, about 6 feet deep, and 4 in diameter at the top, having a picket fixed in the centre of the bottom, 6 feet long, and * Vide FIELD FORTIFICATION, pages 252, 253, 254, 255. 4 or 6 inches square, the point being on a level with the upper surface of the ground. These pits are used to prevent the approach of bodies of cavalry. PERMANENT FORTIFICATION. Remarks, and general rules. The ground plan, and relief of bastioned fortifications are mutually dependent on each other; and, as a variety of causes occur to influence both according to the various sites occupied, it is impossible to give them any fixed arrangement, and dimensions, applicable under all circumstances. However, under the supposition that the site to be fortified is a horizontal plane, a great number, and variety of systems have been proposed at different times; almost every author, who has treated of fortification, having invented one, at least, of his own. Notwithstanding this diversity of opinion, as to the best system, all agree that the following general principles should not be lost sight of in the construction of fortifications. 1. Salient angles should be as large as possible, and never less than 60°. The larger they are, the smaller will be the space in front undefended by direct fire. If less than 60°, the salients of earth are too acute to stand firmly for any length of time; and the angles of masonry are easily damaged; besides which, the space within the parapets becomes too restricted to admit of a gun being worked near the angle. 2. Angles of defence should be right angles, or slightly obtuse. If less than right angles, the fire from the flanking works might injure the defenders of the works they flank; as troops generally, and more particularly at night, fire in a direction perpendicular to the parapet; and if too obtuse, the fire might be directed wide of its object. Besides, embrasures should be cut as direct as possible; as the more they are oblique, the more they weaken the parapet. 3. The length of the lines of defence shall be such, that the works defended may be within the effective range of the projectiles used. 4. The works should be so disposed that the assailants may not be able to obtain cover in any part of the exterior, within range of the projectiles of the defenders. 5. The escarps of the body of the place should be of such height, or construction, as to be secure against escalade. 6. The masonry should be sufficiently covered from the view of the enemy, to prevent his making a practicable breach from a dis tance. 7. The interior of every work should be completely covered from the view of an enemy outside it; so that he may not be able to fire directly into any part of it. Interior works should therefore have a command over those in front of them, at least equal to the height which a besieger can give to the parapets of his lodgments, and which is seldom less than 3 feet. 8. Every opportunity should be seized of so directing the faces of works that an enemy may not have it in his power to enfilade them by ricochet fire. 9. In the general construction of fortifications the salients should be few, and sufficiently prominent to force the besieger to take them before he can attack the re-entering parts. The object of this is to reduce the number of points of attack, as, the fewer they are, the less advantage an assailant derives from his numerical superiority. : 10. Permanent fortifications must be considered very incomplete without a sufficiency of casemated cover for the sick, and wounded, and for the portion of the garrison off duty. The magazines of ammunition and provisions, should also be secure from the effects of shells; and the supply of water ample, and certain. 11. Small enclosed works, in which the defenders must be crowded, without cover from vertical fire, should never be employed in permanent fortification. The strength they impart can never make up for the loss the garrison must suffer by them. 12. Outworks, and detached works should have easy communications with the main work, to admit of their garrisons receiving reinforcements, or supplies, when necessary; and to enable them to retreat, when the works are no longer tenable. 13. Every enclosed defensive work of importance should, if possible, be provided with a keep, or citadel, or interior retrenchment, to which the garrison may retire when the main enclosure (or enceinte) is forced. 14. Outworks, and detached works near the body of the place, should be so constructed that the enemy, when he has taken them, may not be able to use them as defensive works. 15. Outworks, and detached works, should always be of sufficient strength to force the enemy to make regular attacks on them. Advanced works of a weak construction are likely to do more harm than good; for the troops of the garrison seeing them taken with comparative facility, would naturally lose confidence in the strength of their remaining defences, while that of the assailants would be increased by early success. 16. All fortifications should be provided with means of egress, and ingress, to enable the garrison to assume the offensive, whenever opportunities offer; and to admit reinforcements into the fortress. 17. There are very few fortified places that agree with any published system, though some resemble one or other of the systems, or consist of combinations, or modifications of them. The systems which have been wholly, or partly carried into execution are, of course, the most interesting, and form valuable subjects of study. A knowledge of their advantages, and defects, and the best methods of attacking, and defending them, will enable the military student properly to appreciate works which have been, or are to be constructed; and the operations by which fortresses have been, or may be captured. VAUBAN'S FIRST SYSTEM. To describe three Fronts of fortification, on a hexagon. Vide Plate. With a radius of 360 yards, the length of the exterior side of the fortification (taken from a scale of equal parts), describe a semicircle, which divide into three equal parts, and draw lines to the points of division; thus forming three exterior sides. Bisect each of these by perpendiculars drawn to the centre of the polygon, on which set off th of the exterior side, (if a hexagon,)* through which points draw the Lines of defence; on these set off ths of the exterior side, from the angles of the circumference, for the length of the faces of the bastions; with radius of the distance between the two faces describe arcs joining the lines of defence, and draw the chord of these arcs for the flanks of the bastions; a line joining the interior extremities of the flanks will give the length of the curtains. Or, to describe one Front of fortification. For the exterior side, draw a line 360 yards in length, at the ends of which, lines are to be directed to the centre of the polygon, at the angle required; (vide PRACTICAL GEOMETRY-To find the angles at the centre, and circumference of a regular polygon,) then bisect the exterior side, and draw the perpendicular, &c., &c., as described, above, for the construction on a hexagon. Main ditch. From the salient angles of the bastions, with 38 yards as a radius, describe arcs, to which draw tangents, directed to the angles of the shoulders of the bastions. The Tenaille. Draw lines parallel to the lines of defence, at the distance of 16 yards, for the faces of the work; its flanks, and curtain are constructed parallel to the flanks of the bastions, and curtain, at the distance of 11 yards. The Ravelin. From the re-entering angle of the counterscarp, make the capital of the ravelin 80 yards in length, and from its summit draw lines to points, on the faces of the bastions, 11 yards from the angle of the shoulder; the junction of these lines, and the counterscarp of the main ditch will determine the length of the faces of the ravelin. The gorge is formed by drawing lines 24 yards from the re-entering angle of the counterscarp to the intersection of the perpendicular, and the exterior side. From the salient angle of the ravelin, with a radius of 24 yards, describe an arc, to which draw tangents parallel to the faces, for the breadth of the ditch. *For a square, the length of the perpendicular is 1-8th the exterior side; for a pentagon 1-7th; for the hexagon, and other polygons, 1-6th. |