Part 148

Area, the superficial content of a rampart, or other work.

Arrow, is a work placed at the saliant angle of the glacis, and consists of two parapets, each about 40 fathoms long; this work has a communication with the covert-way, of about 24 or 28 feet broad, called a caponniere, with a ditch before it of about 5 or 6 fathom, and a traverse at the entrance, of three fathom thick, and a passage of 6 or 8 feet round it.

Banquette, whether single or double, is a kind of step made on the rampart of a work near the parapet, for the troops to stand upon, in order to fire over the parapet: it is generally 3 feet high when double, and 1¹⁄₂ when single, and about 3 feet broad, and 4¹⁄₂ feet lower than the parapet.

Bastion, is a part of the inner inclosure of a fortification, making an angle towards the field, and consists of 2 faces, 2 flanks, and an opening towards the centre of the place, called the gorge: or it is rather a large mass of earth, usually faced with sods, sometimes with brick, but rarely with stone; having the figure described.

With regard to the first invention of bastions, there are many opinions amongst authors. Some have attributed this invention to Zisca, the Bohemian; others to Achmet Bashaw, who having taken Otranto in the year 1480, fortified it in a particular manner, which is supposed to be the first instance of the use of bastions. Those who wrote on the subject of fortification 200 years ago, seem to suppose, that bastions were a gradual improvement in the ancient method of building, rather than a new thought, that any one person could claim the honor of. It is certain, however, that they were well known soon after the year 1500; for in 1546, Tartalea published Quesiti & inventioni diverse, in the 6th book of which he mentions, that whilst he resided at Verona (which must have been many years before) he saw bastions of a prodigious size: some finished, and others building: and there is besides, in the same book, a plan of Turin, which was then fortified with 4 bastions, and seems to have been completed some time before.

The great rule in constructing a bastion is, that every part of it may be seen and defended from some other part. Mere angles are therefore not sufficient, but flanks and faces are likewise necessary. The faces must not be less than 50 fathom, nor more than 65. The longer the flanks are the greater is the advantage which can be derived from them. They must therefore stand at right angles with the line of defence. At the same time the disposition of the flanks makes the principal part of a fortification, as on them the defence chiefly depends; and it is this that has introduced the various kinds of fortifying.

The angle of the bastion must exceed 60°; otherwise it will be too small to give room for the guns, and will either render the line of defence too long, or the flanks too short. It must therefore be either a right angle or some intermediate one between that and 60 degrees.

Full bastions are best calculated for intrenchments, which are thrown up at the gorge, or by means of a cavalier, whose faces are made parallel to those of the bastion at the distance of 15 toises; having its flanks at the distance of 12 toises, and a ditch measuring 5.

Large bastions have the advantage of small ones, for this palpable reason; the bastion being considered the weakest part of the body of a place, is always attacked; when there is room for troops, cannon and mortars, its natural weakness is greatly remedied.

Gorge of a bastion, the interval between the extremity of one flank and that of the next.

Flat bastion. When a bastion upon a right line is so constructed, that its demi-gorges do not form an angle, it is called a flat bastion.

Gorge of a flat bastion, is a right line, which terminates the distance between two flanks.

Solid bastion, Full bastion, A bastion is said to be solid or full, when the level ground within is even with the rampart; that is, when the inside is quite level, the parapet being only more elevated than the rest. Solid bastions have this advantage over others, that they afford earth enough to make a retrenchment, in case the enemy lodge themselves on the top of the bastion, and the besieged are resolved to dispute every inch of ground.

Hollow bastion, Empty bastion, is that where the level ground within is much lower than the rampart, or that part next to the parapet, where the troops are placed to defend the bastion. The disadvantage of these kinds of bastions is, the earth being so low, that when an enemy is once lodged on the rampart, there is no making a retrenchment towards the centre, but what will be under the fire of the besiegers.

Detached bastion, is that which is separated or cut off from the body of the place, and differs from a half moon, whose rampart and parapet are lower, and not so thick as those of the place, having the same proportion with the works of the place. Counter-guards with flanks are sometimes called detached bastions.

Cut bastion, is that whose saliant angle or point is cut off, instead of which it has a re-entering angle, or an angle inwards. It is used, either when the angle would, without such a contrivance, be too acute, or when water, or some other impediment, prevents the bastion from being carried to its full extent.

Composed bastion, is when two sides of the interior polygon are very unequal, which also renders the gorges unequal; it may not improperly be called a forced bastion, being as it were forced into that form.

Deformed bastion, is when the irregularity of the lines and angles causes the bastion to appear deformed, or out of shape.

Demi-bastion, is composed of one face only, has but one flank, and a demi-gorge.

Double bastion, is that which is raised on the plane of another bastion, but much higher; leaving 12 or 18 feet between the parapet of the lower, and the foot of the higher; and is sometimes in the nature of a cavalier.

Regular bastion, is that which has its true proportion of faces, flanks, and gorges.

Irregular bastion, is that wherein the above equality of just proportion is omitted.

Barriers, in fortification, a kind of rails to stop the horse or foot from rushing in upon the besieged with violence. In the middle of this kind of defence there is a moveable bar of wood, which opens or shuts at pleasure.

Berm, is a little space or path, of 4 to 8 feet broad, between the ditch and the talus of the parapet; it is to prevent the earth from rolling into the ditch, and serves likewise to pass and repass. As it is in some degree advantageous to the enemy, in getting footing, most of the modern engineers reject it.

Bonnet, in fortification, is a sort of work placed before the saliant angle of the ravelin to cover it: it consists of 2 faces, parallel to the ravelin, or perpendicular to those of the lunette. They are generally made 10 fathom broad at the ends with a ditch of the same breadth, the covert-way 6, and the glacis 20 fathom.

Breach, is on opening or gap made in a wall or rampart, with either cannon or mines, sufficiently wide for a body of troops to enter the works, and drive the besieged out of it.

Practical breach, is that where men may mount, and make a lodgment, and should be 15 or 20 feet wide.

Capital of a work, is an imaginary line which divides that work into two equal parts.