Part 150

When there is a cunette, there should be a caponniere to flank it.

Defilement, in fortification, is the art of disposing all the works of a fortress in such a manner, that they may be commanded by the body of the place. It also includes the relative disposition of the works, and the ground within cannon shot, so that the one may be discovered, and the other not observed.

Demi-gorge, is half the gorge, or entrance into the bastion, not taken directly from angle to angle, where the bastion joins the curtain, but from the angle of the flank to the centre of the bastion, or rather the angle the two curtains would make were they protracted to meet in the bastion. Mr. Landmann determines it to be the line which is formed by the prolongation of the curtain meeting the oblique radius.

Demi-lune. See RAVELIN.

Descents in fortification, are the holes, vaults, and hollow places made by undermining the ground.

Descents into the ditch or fossé, are boyaux or trenches effected by the means of saps in the ground of the counterscarp, under the covert way. They are covered with madriers, or hurdles, well loaded with earth, to secure them against fire. In ditches that are full of water, the descent is made even with the surface of the water; and then the ditch is filled with fagots, fast bound, and covered with earth. In dry ditches the descent is carried down to the bottom; after which, traverses are made either as lodgments for the troops, or to cover the miner. When the ditch is full of water, the descent must be made over its surface; which is done by securing it with blinds or chandeliers, from being enfiladed, or by directing the course of the descent from the point of enfilade in the best way you can.

Detached bastion. See BASTION.

Detached redoubt. See REDOUBT.

Ditch, in fortification, is a large deep trench made round each work, generally from 12 to 22 fathom broad, and 15 to 16 feet deep: the earth dug out of it serves to raise the rampart and parapet. Almost every engineer has a particular depth and breadth for ditches; some are for narrow ones and deep, others for broad ones and shallow; and it is most certain that ditches should be regulated according to the situation. In regard to wet and dry ditches, almost all authors have given it in favor of the latter; and we shall only add, that the best of all are those which can either be filled or kept dry at pleasure.

Wet ditches, which have stagnant waters, are liable to great inconveniences. They are said to be well calculated to prevent sudden surprises and assaults; but we are convinced of the contrary, especially during a hard frost. Some again assert, that they stop all communication between ill-disposed persons in the garrison and the besiegers. Every man with the least experience, must be of a different opinion.

Wet ditches might certainly be so constructed, as to let the surface of the water remain 12 or 15 feet above the level of the adjacent country. In which case they would serve as large reservoirs, and not only contribute to the defence of a fortified place, but enrich the grounds by being occasionally let out. The additional value which the neighboring meadows would bear from these seasonable overflowings, might in some degree compensate for the expence of the fortification. During a siege, these waters, with proper management, must give considerable uneasiness to the enemy that invests the place.

To answer this double purpose, the ditch must be separated into several large basons, which might be filled or emptied at discretion, as often as circumstances would require.

Dry ditches. There are some ditches which may be filled at will; and others which cannot, except by extraordinary means. If they should be intended to answer the purpose of agriculture, aqueducts might be constructed, or the waters poured in through artificial channels. In which case the ditches would not require much depth. The glacis might be raised in such a manner as to serve to dam in the body of water, and to afford a second glacis from whence the besieger might be considerably embarrassed.

Ditches that are lined, ditches whose counterscarp is supported, and kept up by a stone or brick wall.

Ditches that are not lined, whose counterscarp is supported by earth covered with sods. These ditches are not so secure as the former, on account of the breadth which must be given to the talus, and by which an enemy might easily surprise a place.

So that ditches in fortification may be briefly distinguished under three separate heads, viz:

Dry ditches, which from the facility with which they may be repaired, and their capability of containing other works proper for their security, are in most instances preferable to any others.

Wet ditches that are always full of water, and consequently must have bridges of communication which are liable to be destroyed very frequently during a siege.

Wet ditches are subject to many inconveniences, are ill calculated to favor sallies, and have only the solitary advantage of preventing a surprise.

The third sort of ditch has all the advantages of the other two kinds; if, as we have just observed, it can be so contrived, as to admit water occasionally into the different basons by means of aqueducts, and be drained, as circumstances may require.

Draw-bridge. See BRIDGE.

Embrasures. See EMBRASURE.

Envelope, is a work of earth raised occasionally in the ditch, sometimes like a plain parapet, at others like a small rampart with a parapet to it. Envelopes are generally made before weak places.

Epaulement. See EPAULEMENT.

Epaule, or the shoulder of the bastion, the angle made by the union of the face and flank.

Escarp. See SCARP.

Esplanade. See ESPLANADE.

Exterior side of a fortification, is the distance, or imaginary line drawn from one point of the bastion to that of the next.