can have no fixed rule; they are general- We now come to speak of that crown- Redoubts standing in ravelines, being intended as a resort for the troops driven from the defences of its faces, and requir. ing great strength of defenders, should invariably be casemated throughout, in the most substantial manner; they may not only mount batteries on their ramparts, which should command those of the ravelines wherein they are placed, but they may be pierced below with abundance of loop holes, and with embrazures for cannon, provided the ditch be of a sufficient depth and width to prevent assault, and that the interior of the raveline be, as it ought, perfectly level, and contain nothing to conceal the enemy in each redoubt there should be a small expense magazine, and in every outwork one or more wells should be made, if practicable, of sufficient capaci-, to the centre of the polygon E, laid it ty to supply plenty of water. down as a general rule, that the ascent of the works should assimilate to that line; yet in such very spacious defences as crown-works 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 crownwork are defended by still farther advanced out-works: then the angle of defilement would be so acute, from the terre pleine, or horizon, as to cause scarce any difference between the heights of the ravelines and of the bastions of the crown-work; 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 entrenchments 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 salient 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 serviceable in the smallest degree to the enemy, and to blow them up, whenever a favourable moment may present itself. 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 success. ful 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 casement. But 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,, 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 Ň. The entrenchments, ff, cut the ram parts 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 salient angle of the raveline, that the bastions of the crownwork 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 crownwork, such as lunettes, tenailles, tenaillons, feches, 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 This out-work faces of the bonnet. comes down to the lunettes, by which it is flanked. We now have to treat of those important parts, the glacis, and the covertway. 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 posts. 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 rail. The primary defences are in the covert-way, 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 covertway are sometimes abandoned from vaat every forty rious causes, there are 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 The traverses men to pass abreast. may be about six feet high within, and about five without; there is a banquette within which raises the defenders about The glacis is always made so as to give An extensive defence, called a hornThe latter, as may be work, is sometimes substituted for a crown-work. 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 be yond a crown-work. The object of both these defences, generally, is much the same; when a small diminishing tract is to be covered, the horn-work is proper, but when a round, or rather increasing, spot is to be enclosed, the crown-work should be preferred. The intrenchments 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 crown-work, where the intrenchments, ff, are narrower than the front which can be opposed to them, be tween 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 44feet above the banquette I, and 71 above the terre-pleine H. The upper part of the parapet is lower with out 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 like wise 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 in calculable 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 0; 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 counter-guard 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, rivetted 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 spirituous 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 palisades, standing on a shelv ing 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 para pets, should be regularly mown for the same purpose. The counterguard B is solid, as is also the rampart A; its terre-pleine H is considerably lower than that of A, which commands 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 at x. In this counterguard the interior of the parapet is not reveted; therefore the banquette I, ascended from the terre-pleine, H, by a slope of gazon. The parapet C, &c. are nearly 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 terrepleine H, but its parapet is faced 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 heigh 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 embrazures would allow the guns to play into the covert way. It is 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 difficul ty of breaching the saliant angles of outworks. VOL. V. 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 always 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 defilement, 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 prin ciples 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 bat. tered from the glacis, DO, without touching C or B. To remedy this, where such an_exposure would be injurous, (for it is Dd |