Lunettes are generally constructed by producing their faces at about one half the length of the raveline which they flank at right angles ; their own flanks are drawn perpendicular to the face of the bastion which commads them, generally falling about the middle of such face. See the lunette a, opposite the bastion D. Sometimes the lunette is separated, by a narrow fosse, from the body of the rave line ; in other instances, its face joins that of the raveline ; the fosse being arch ed over, and a battery placed on the arch, by which the ditch of the raveline is secured. The face of the lunette gives a direct fire towards the glacis, before the salient angle of the bastion 5.
Tenaillons, (signifying piercers, or claws,) are sometimes made on each side of a raveline, and even beyond them a small detached raveline, or a bonnet, is sometimes added. The rule for con structing a tenaillon is, to prolong the other face of the raveline, thereby to make its front, and to determine the length of that front, by a flank drawn per pendicular to the centre of the face of that bastion before which the tenaillon stands; as is seen in the tenaillon stand ing in front of the bastion 4, and covering the face of the raveline K.
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 ram parts, which should command those of the ravelines wherein they are placed, but they may be pierced below with abundance of loop holes, and with em. brazures for cannon, provided the ditch be of a sufficient depth and width to pre vent assault, and that the interior of the raveline be, as it ought, perfectly level, and contain nothing to conceal the ene my : 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 ty to supply plenty of water.
Redoubts made to flank other works can have no fixed rule ; theylare general. ly placed to most advantage, and their fronts are always disposed towards those parts of the exterior which stand in need of such support. In some places, as at Q, they are made more to cover a weak point, than with any immediate view to protracting the assault : the want of a re doubt, or some other work, on the other side of the bastion 0, serves to prove the utility of that at Q; it being evident, that could an enemy's battery be placed any where about C°, C°, thatis, in a position to batter the bastion 3, the greater part of the defences of the principal would be subjected to mischief ; and that, as the approaches should advance upon the gla cis, the ravelines N, and 0, would be in a measure cut off from all connection with the curtains S r, u v. We suppose the
crown-work M not to exist.
We now come to speak of that crown. work ; it is a limb of immense impor tance, and should be rendered as strong and efficient as possible. This kind of fortification is built on various accounts, viz. to occupy ground which, being left at the disposal of an enemy, might prove of considerable injury to the body of the place ; to enclose buildings that could not be included within the principal ; to de fend a promontory, or a projection, cover ing a harbour; to prolong a line of works, and other causes which locality would suggest. When, however, a piece of ground, which stands higher than could be commanded from the works of the principal, is to be occupied, a crown-work would be improper : in such case, a cita del is advantageously made on the supe rior ground ; observing, that in lieu of a raveline being at N, there should be a complete defensive face, appertaining to the citadel, commanding the works of the fortress, which, instead of presenting de fences along the centre face B C, should rather lay open to the batteries of the citadel. These latter should command the whole interior of the polygon, and be well casemated throughout, for the safe lodgment of all the garrison, and for the safe keeping of provisions and stores for six months at least. The instan ces on record of citadels holding out for a long time should render their use more common, especially where the ground fa vours their command of allth e other works.
Although we have in tracing the de filement of the ramparts, from the point 0, to the centre of the polygon E, laid it down as a general rule, that the as cent of the works should assimilate that line ; yet in such very spacious de fences 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 rave lines opposite to the faces of the crown work are defended by still farther ad vanced outworks: then the angle of de filement 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 im propriety. Hence it is often necessary to give the ramparts of a crown-work rather more height than the line of de filement might allow ; raising the rave line 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 rnoineau, or flat bastion, of similar height with the cavaliers, may be made in the centre of the curtain u v, for the same purpose.