their use more common, especially where the ground favours their command of all the other works.

Although we have, in tracing the defilement of the ramparts, from the point, to the centre of the polygon E, laid it down as a general rule, that the ascent of the works should assimilate to that line; yet in such very spacious defences as crownworks sometimes are, (for their area is occasionally equal to a third of that within the interior line of the polygon,) some exceptions will take place; especially when the ravelines opposite to the faces of the crown-work, are defended by still farther advanced out-works: then the angle of defilement would be so acute, from the terrepleine, or horizon, as to cause scarce any difference between the heights of the ravelines, and of the bastions of the crownwork: a matter of obvious impropriety. Hence, it is often necessary to give the ramparts of a crown-work, rather more height than the line of defilement might allow; raising the raveline and its intenchments suitably, and making cavaliers, as instanced in the bastion C, of the crown-work, on the solid bastions 3 and 4, so as to command the whole of the crown-work completely. A moineau, or flat bastion, of similar height with the cavaliers, may be made in the centre of the curtain uv, for the same purpose.

Cavaliers are of singular use on many other occasions, to which their form should be accommodated; that in the bastion c of the crown-work, is, from its shape, termed a horseshoe; the flatness of its front is applicable to the situation it there holds, because it opposes a direct fire towards the point; but its circular tendency gives its front a bias towards the inner parts of the faces of the ravelines, while its flanks present a direct fire into the ravelines themselves, and give an oblique fire into the opposite ditches, whereby the assault of breaches in the saliant angles of the demibastions bb, would become very hazardous. The proportions of a crown-work must depend greatly on the purposes for which it is erected, but whatever be its object, the whole of its defences should be commanded by the works of the principal in so complete a manner, that no part, whatever, should offer an asylum to the enemy, after carrying it; and consequently, that none of its batteries should be able to play into any other of the defences. For the loss of so large a limb, and of the many serviceable cannon, platforms, &c. which, in such

case are invariably, and actively employed against the body of the place, is a very serious concern, and requires the utmost exertion to oppose even for a time. On this account it is highly necessary to have mines under all those parts which can prove ser viceable in the smallest degree to the enemy, and to blow them up whenever a favourable moment may present itself.

But

From what has been stated as to the purposes of crown-works, it will be seen, by reference to that laid down in the plate, that much attention is requisite to give them every defensive property, while on the other hand they should prove of little value to a successful assailant. The only work in our plan affected by such a circumstance, would be, that the counterguard 7 would be untenable as a battery, though it might retain some small utility as a casemate. by mining all the inner part of the flank, which commands the counterguard, even that evil would be lessened; if, however, an enemy should be able to carry the raveline N, and to maintain his ground therein, notwithstanding the tremendous fires from the faces of the bastions 3 and 4, and from the curtain u v, (all of them direct) but little hope could remain of a successful resistance, and the counterguard would be, comparatively, no sacrifice. We, however, see from this, that a tenaille on the lines of defence t, u, w, as shewn at P, between the bastions 2 and 3, must prove highly serviceable, especially if mounting such heavy metal as would destroy any works thrown up in the raveline N.

The intrenchments ff, cut the ramparts of the flanks of the crown-work through all but the revetement, and they are carried as far forward as possible, so as barely to be flanked by a barbet battery in the saliant angle of the raveline, that the bastions of the crown-work may be perfectly commanded by musquetry. The cavalier in C, is supposed to be mined and destroyed, else it would prove very disadvantageous to the defence of the raveline, which it would partly command.

We have already observed, that many out-works might be shewn in addition to those given to the faces of the crown-work, such as lunettes, tenailles, tenaillons, fleches, advanced lunettes, redoubts, bonnets, &c. but we apprehend the reader will, from the foregoing details, and the plate to which they refer, be able to supply to his imagination, the almost endless continuation of outworks, which the limits we are compelled

to draw around this branch of science preclude us from enlarging upon.

The bonnet mentioned in the preceding paragraph, is nothing more than an angle made parallel to a raveline, and not far removed from it, so that the faces of the latter command the faces of the bonnet. This out-work comes down to the lunettes, by which it is flanked.

We now have to treat of those important parts the glacis, and the covert-way. The former is a gradual slope, commencing at a distance from the exterior of the out works, seldom less than fifty yards, and when within five toises of the ditch, stops abruptly, occasioning a sudden fall, never less than seven, nor should it be more than nine, feet. Here it is supported by a revetement, and is partly met by a banquette of turfed soil, which is raised high enough to come within four feet and a half of the crest, or highest part of the glacis. At the foot of the revetement, at such distance as may prevent an enemy jumping over, say from two to three feet off, a row of palisades is fixed; these are strong pales nine feet in length, of which one third is buried in the banquette, while the long horizontal rails to which the palisades are firmly nailed, are at every ten feet morticed into square ports. The lower rails are one foot from the banquette, and the upper ones are just level with the crest of the glacis, so that the soldiers may fire through the top intervals between the pales, resting their pieces on the upper rai!.

The primary defences are in the covertway, but they are only for musquetry; as this part, owing to its laying very low, is subject to be enfiladed, and also because the saliant angles of the covert-way are sometimes abandoned from various causes, there are at every forty or fifty yards parapets, whose slopes point towards the exterior, or saliant angle of the covert way, so that cannon shot may be stopped, and the defenders may make a stand from time to time, behind these parapets, (which are called traverses,) until at last forced into the out-works for safety from the pursuing enemy. Each traverse is made the whole breadth of the covert-way, namely, 30 feet; their exterior ends would touch the palisades, were not little inlets made at right angles into the crest of the glacis, broad enough for two or three men to pass abreast. The traverses may be about six feet high within, and about five without; there is a

banquette within which raises the defenders about a foot and a half, for them to stand upon, and to fire over the parapet, of which about ten feet is generally the thickness. Another method of passing the ends of the traverses is not uncommon, and is, perhaps, at least equally good as the foregoing; this is by making a serrated line of palisades, as seen in the plate, in which the small black projections from the line of the ditch, represent the traverses, and the line bordering the glacis g, g, g, shews the line of the palisades; not unlike the teeth of a key-hole saw. The vacant spaces +, +, +, +, in the re-entering angles, are for the assembling of troops for the defence of the covert-way, and are called places of arms. In these, sometimes, small redoubts are thrown up. Places of arms are always near to some sortie from an outwork, so that the parties posted in them may be readily withdrawn, or be reinforced; in some instances, however, places of arms are made in the saliant angles of the covert-way; but they should then be in some measure entrenched, or protected; else they would be severely, and perhaps unnecessarily exposed, although the covert-way is so far above their heads.

The glacis is always made so as to give an inclined plane, corresponding with every change of direction in the line of the crest of the glacis; not, however, adverting to the small inlets, or serrated appearance, required for passing the ends of the traverses. This will be seen on reference to the plate, where every such inclined plane is particularized. Such a disposition of the glacis is indispensable; it gives the true direction of every part, as it respectively stands fronting to the line of palisades; so that the soldiers can scarcely fail to aim properly if they fire straight before them, and rest their musquets on the upper rail. They thus graze the surface of the glacis, and consequently do great execution.

An extensive defence, called a hornwork, is sometimes substituted for a crownwork. The latter, as may be seen, is composed of a full bastion between two curtains, whose exterior sides are terminated by demi (or half) bastions; whereas the horn-work, in lieu of expanding as it recedes from the principal, contracts, and its front, (which should be parallel to that of the principal when it covers a curtain therein,) is formed only of a curtain, terminated by two demi-bastions. The out

works beyond its ditch may be very numerous, though not so varied as those placed beyond a crown-work.

The object of both these defences, generally, is much the same; when a small diminishing tract is to be covered, the hornwork is proper, but when a round, or rather encreasing spot is to be enclosed, the crownwork should be preferred. The intrench menis within a horn-work are, however, the strongest, because they oppose a larger front against a smaller one; which is the reverse of what takes place in the crownwork, where the intrenchments ƒ ƒ, are narrower than the front, which can be opposed to them between the flanked angles of the demi-bastions b b.

"The explanation of fig. 2, next demands our attention: it is the profile of the principal, and of the proximate outwork. In this, not only the defilement, but the deviations from the terre-pleine, or line of the horizon, whether by superstructure or by excavation are shewn.

A, represents the rampart of the principal, or body of the places of which the measurements may be in general terms taken at the following computation. The height of the terre-pleine H, on which the cannon are mounted, 20 feet; the banquette I, on which the soldiers stand to fire their small arms, raised 3 feet above H; the point X, which is the crest of the parapet, being 44 feet above the banquette I, and 7 above the terre-pleine, H. The upper part of the parapet is lower without than it is at the crest X. This declination, which is called the superior slope, is at the rate of one inch for every foot the parapet has of thickness, so as to allow the defenders to fire at an enemy almost close to the rampart, yet not to weaken the crest. K, shews a revetement of masonry, which should be five feet thick at the top of the rampart, not including the parapet, but measuring at the upper cordon O. The exterior slope of the revetement should be one sixth of its height, taken from the foot to the cordon. The foundation should project in proportion to the height, and to the nature of the soil. The interior slope of the parapet, and the banquette, are likewise bounded by a revetement in this figure, but such is not always the case, when it is, the ascent to the banquette is made by two or three steps, as here shewn. Nor are all parapets faced with masonry; the generality, indeed, are gazoned, or turfed, on account of the incalculable injury done by the splinters,

knocked off by such shots as graze upon masonry of any kind. In some instances, only half revetements are used, that is, only for the scarp, or face of the ditch, as seen at M under the cordon O; the whole exterior of the rampart itself being gazoned. The interior slope of the rampart, when made of masonry, as seen at P, where the counterscarp is carried up, or built upon, to form the interior slope of the counterguard B, may be equal to only one-fifth of its whole height; but where masonry is not used, the interior slope, as at L, of the rampart A, should, if the soil be firm, be equal to the height of the rampart, which would give an angle of 45 degrees: when the soil is sandy, crumbly, or apt to give way, the interior slope should be equal to a height and a half, or even more, if circumstances should require. The continuation of the revetement M, above the cordon O, which is level with the terre-pleine of the berm N, is a firm parapet, made in lieu of the exploded fausse-braye, to prevent the ruins of the rampart A, when breached, from falling into the ditch C; of which the breadth is indefinite, though from 15 to 25 toises may be considered as the limits for works according to the mean, and great systems of Vauban. About the middle of the ditch, but generally rather more towards the counterscarp P, than towards the scarp M, is the cunette, or cuvette, about 15 feet broad, reveted throughout, and from six to nine feet deep. It is always kept full of water, where that may be practicable; and as it goes entirely around the body of the place, serves to prevent a surprise, to restrain from desertion, also from an improper access to spiritous liquors, and as a drain to the body of the ditch. In many instances, very fine supplies of fish are obtained from the cuvette. In some fortresses it is cut off from before the curtains by rows of pallisades, standing on a shelving work, called a batardeau. Where it is continued before the curtains, there must be bridges of communication; and small temporary plank passages are made over in various parts, when occasion may require. All ditches should be sown with good grasses, that they may give a supply of that valuable commodity to such horses, &c. as may be kept in the fortress; and all gazoned facings, as well as the slopes of parapets, should be regularly mown for the same purpose.

The counterguard B is solid, as is also the rampart A; its terre-pleine H is consi.

at x.

derably lower than that of A, which command it, both by the cannon it mounts, and by its musquetry; the parapet being sloped so as to give a direct fire into it, when the firelocks are laid upon the slope In this counterguard the interior of the parapet is not reveted; therefore the banquette I is ascended from the terrepleine, H, by a slope of gazon. The parapet C, &c. are nearly of the same dimensions as F on the rampart A, except that the rampart B is much lower than A. The exterior of B has a cordon, level with the terre-pleine H, but its parapet is fared with turf, which the cordon assists to support. If the counterguard B were not defended by other out-works in its front, it would have a glacis come close to it, leaving only a very small passage between its exterior and the palisades; here we suppose it to have a small dry ditch D, reveted both in the scarp and counterscarp, but without a berm, which is very rarely, if ever, allowed to an outwork.

The third figure affords a more general profile of the works, and gives some idea of the usual defilement of the outworks, B and C, from the body of the place A. D is the foot of the glacis, where it meets the terre-pleine, or level of the country, which we always suppose to be esplanaded, (that is, laid flat) and not affording any cover to the enemy for at least 1000 yards from the outworks. The glacis is usually made full 50 yards long, and of such an ascent as to give, on an average, about eight feet height at its crest. Supposing the angle of the raveline to be 25 yards within the crest of the glacis, the continuation of the ascent would strike the cordon of the rampart, C, at 12 feet from the level of the terre-pleine; this determines the height at which a cannon, standing on the terre-pleine of the raveline, C, would graze the glacis, while the slope of the embrasures would allow the guns to play into the covert way. It is to be observed, that, according to this construction, all the scarp, below the cordon, is completely hid from the enemy, and cannot be battered so long as the crest of the glacis remains at its proper height. Hence partly arises the great difficulty of breaching the saliant angles of outworks.

Now let us estimate the redoubt, B, at 25 yards within the flanked angle of the bastion, C. It is to be remarked, that this defence is made with the view to render the raveline untenable to an enemy; and that, for the preservation of its parapet,

the rampart of the redoubt, B, should be a mere trifle above the level of that of the raveline, C. The faces of the contiguous bastions of the same front, enfilade the faces of the raveline; but it is also requisite, that the fire from the curtain should, on emergency, (for the bastions may be silenced) contribute to drive the assailants from that part of the raveline which lays beyond the redoubt, at all events to clear its ramparts. Therefore, we will state the terre pleine of B, at only one foot above that of C. This puts the redoubt completely out of the line of defilément, and, in fact, generates another, by allowing the curtain, A, to throw shot into C, without touching any part of B, as may be seen by following the line from the cordon of A to the terre-pleine of C. Hence B cannot be battered from the glacis.

But where it is necessary to produce the greatest accumulation of strength against any exterior point, it is often found proper to raise every part of the interior defences, so that they should all overlook like a flight of steps, as shewn in fig. 4, where the citadel is supposed to stand on a conical hill, high above the town, (which is only defended by a glacis and covert way, surrounding a ditch and rampart) and has four rows of cannon, at different heights, each commanding the exterior defences, and the surrounding country, as far as the shot can reach. This, though not a common figure, nor a common mode of fortifying such places, (for works are rarely carried like hoops or bands around hills) will fully illustrate the general tendency of the foregoing details, and to the ordinary reader, who cannot here expect to find all the minute items and varieties abounding in this very intricate science, will give a tolerable insight into the principles on which fortifications are usually constructed.

To return to fig. 3. It will be seen that the elevation of A would, on the calculation there assumed, be such as to carry the cordon of its terre-pleine so high, that its revetement could be battered from the glacis, D O, without touching C or B. To remedy this, where such an exposure would be injurious, (for it is in some instances expedient, as above described, to direct all the force exteriorly, especially where the outwork lays upon a navigable river, and that ships can be brought to bear upon the works,) the redoubt must be lowered to the same level of terre-pleine as the raveline; and, indeed, it may even, in some few in

stances, where A must be completely screened from the exterior, be proper to sink the terre-pleine of B so very low, that its cannon may just graze the terre-pleine of the raveline, C; making the parapet of a due height, and forming a substantial shed of three inch boards, &c. nearly flat, over the banquette, at a foot above the crest of the parapet. This prevents the enemy from commanding the terre-pleine of the redoubt, while, at the same time, those defending it, would do ample execution through the narrow slit, or opening, between the crest and the shed. The latter would effectually keep off grenades, &c. and give the defenders great confidence. The dotted lines above the rampart, A, shew the height to which its parapet would necessarily be raised, if B were elevated even a foot and a half only above C. The dotted line from C towards B, shews the level to which the genouliere, or crest of the lower slope of the embrasure, may be brought, so as to allow the fire from B to graze the terrepleine of C, and to drive the enemy from the raveline.

Relinquishing the explanation of what relates to the more scientific parts of the topic, we must now enter upon the description of many other matters, indispensably necessary on this occasion. We have already spoken of bomb-proofs. These are vaulted chambers, either running under long arches, or groined, and standing on substantial walls and pillars. The term very properly implies, that the arches should be suffi ciently strong to resist the fall of shells, or, at least, to prevent their penetrating into the chambers. It generally demands, at least, a yard in thickness to produce such a firm resistance; the masonry should be of the very best materials, and put together in a workmanlike manner. The casemates, thus arched over, should be further covered with three or four feet of soil, where such an addition would not raise the terre-pleine too high; for, by allowing a shell to bury itself completely, its splinters do not occasiou half so much mischief, as when the explosion is more superficial; although a quantity of soil may be thrown out. Perhaps the best contrivance for small casemates, defended by breast-works, is the giving them such a slope, as may cause shells to fall into pits, &c. so as to do no damage. Such pits answer well in the centres of round or polygon redoubts, where only a parapet is left around the top, and

might, perhaps, be advantageously made in the centre of block-houses, &c.

In the formation of magazines, for ammunition, the arches are usually made double, that is, one greater arch covers two smaller ones; the latter resting on a central pier, as seen in fig. 5. In this case every arch should be bomb proof, and the roof should be pitched; the end falling off by a gradually rounding, and the whole well supported by buttresses. The walls of magazines are generally double; the buttresses are sometimes pierced at their sides with small loopholes for the admission of air and of light to the surrounding passage. All the fastenings should be of brass or of copper, and no wood or iron allowed in any part what

ever.

The ramparts are ascended by means of long slopes, called ramps, laying in general parallel with, and leaning against them; these ought always to be broad enough to admit a gun passing up and down, mounted on its carriage. The ramps into solid bastions sometimes diverge into three branches, of which two lay along the insides of the adjoining curtains, while the third runs straight up in a line with the capital, i. è. with the centre of the gorge, pointing towards the saliant angle. Thus HC is the capital of the bastion 4, fig. 1. Horseshoe cavaliers have usually but one ramp, placed in the centre of the rear, as shewn by the two parallel lines proceeding from that in the bastion, C, of the crown work, M, fig. 1.

The proper arrangement of streets, within fortified towns, is of the utmost im portance, by contributing essentially to the ready resort of troops to their posts, and facilitating the supply of stores. Every avenue ought to have a barrier, both to keep the inhabitants under proper controul, and to prevent the effects of various stratagems in behalf of a surprise. Those houses which command the interior of the works should be always reserved for the habitations of the garrison, and should likewise be supplied with small quantities of ammunition. The arsenals should be completely covered from the fire of the enemy's batteries; and, toge ther with every building appropriated to the lodgment of troops, or of stores, &c. should be covered in with bomb proofs. The magazines should not be too large, but commodiously situated for the distribution of ammunition, and every precaution should be taken to keep all combustible stores, as