Part 154

Works. All the fortifications about a place, are called the works of a place.

Out-works. All detached works in a fortification are so called. See Dehors.

Zig-Zag. See SIEGE.

The principal maxims of fortification, are these, viz. 1. That every part of the works be seen and defended by other parts, so that an enemy cannot lodge any where without being exposed to the fire of the place.

2. A fortress should command all places round it: and therefore all the out works should be lower than the body of the place.

3. The works farthest from the centre should always be open to those that are nearer.

4. The defence of every part should always be within the reach of musquet shot, that is, from 120 to 150 fathoms, so as to be defended both by ordnance and small fire arms; for if it be only defended by cannon, the enemy may dismount them by the superiority of their’s, and then the defence will be destroyed at once; whereas, if a work is likewise defended by small arms, if the one be destroyed, the other will still subsist.

5. All the defences should be as nearly direct as possible; for it has been found by experience, that the soldiers are too apt to fire directly before them, without troubling themselves whether they do execution or not.

6. A fortification should be equally strong on all sides; otherwise the enemy will attack it in the weakest part, whereby its strength will become useless.

7. The more acute the angle at the centre is, the stronger will be the place.

8. In great places, dry ditches are preferable to those filled with water, because sallies, retreats, succors, &c. are necessary; but, in small fortresses, wet ditches, that can be drained, are the best, as standing in need of no sallies.

Field FORTIFICATION is the art of constructing all kinds of temporary works in the field, such as redoubts, field forts, star forts, triangular and square forts, heads of bridges, and various sorts of lines, &c. An army intrenched, or fortified in the field, produces, in many respects, the same effect as a fortress; for it covers a country, supplies the want of numbers, stops a superior enemy, or at least obliges him to engage at a disadvantage.

The knowlege of a field engineer being founded on the principles of fortification, it must be allowed, that the art of fortifying is as necessary to an army in the field, as in fortified places; and though the maxims are nearly the same in both, yet the manner of applying and executing them with judgment, is very different.

A project of fortification is commonly the result of much reflexion; but in the field it is quite otherwise: no regard is to be had to the solidity of the works; every thing must be determined on the spot; the works are to be traced out directly, and regulated by the time and number of workmen, depending on no other materials than what are at hand, and having no other tools than the spade, shovel, pick-axe, and hatchet. It is therefore in the field, more than any where else that an engineer should be ready, and know how to seize all advantages at first sight, to be fertile in expedients, inexhaustible in inventions and indefatigably active.

Quantity and quality of the materials which are required in the construction of field-fortification.

1. Every common fascine made use of in the construction of field works or fortifications, should be 10 feet long and 1 foot thick. A fascine is raised by means of 6 pickets, which are driven obliquely into the earth, so that 2 together form the shape of a cross. These pickets are tied with willows, or birch twigs. It is upon supporters or tressels of this kind, that fascines are made, which are properly fagots bound together with rods, at intervals of 1 foot each in breadth. Six men are required to complete each fascine; viz. 2 to cut the branches, 2 to gather them up, and 2 to bind the fascines. Six men may with great ease, make 12 fascines in an hour. The smaller sort of willows, or birch twigs, are best calculated for this work. The fascines are fastened to the parapet, which would otherwise crumble and fall down. A redoubt, constructed en crémaillere, must have fascines 8 feet long.

2. There must be 5 pickets for each fascine, and each picket must be 3 or 4 feet long, an inch and a half thick, and sharp at one end; they serve to fasten the fascines to the parapet.

3. When you cannot procure wood for the fascines, the parapet must be covered or clothed with pieces of turf, 4 inches thick, and a foot and a half square; these are fastened to the parapet with 4 small pickets 8 inches long.

4. The fraises, or pointed stakes, must be 8 feet long, 5 inches thick, and be sharp at the top. The beams upon which they are laid, must be 12 feet long and 6 inches thick. These beams are spread horizontally along the parapet, and fraises are fixed to them, with nails 7 inches long; after which the beams are covered with earth. Two men will make 12 fraises in an hour.

5. The palisades, by which the ditch or fossé of a work is fortified, must be 9 or 10 feet long, and 6 inches thick; they must, likewise, be sharpened at the end. If you cannot procure them of these dimensions, you must use smaller ones; in which case you will have the precaution to mix a few large stakes.

6. The pickets, which are fixed in trous-de-loup or wolf-holes, must be 6 feet long, 4 inches thick, and sharp at the top.

7. The beams belonging to a cheval-de-frize must be 12 feet long, and 6 inches broad. The spokes which are laid across, must be 7 feet long, 4 inches thick, and placed at the distance of 6 inches from each other. These chevaux-de-frizes are made use of to block up the entrances into redoubts, to close passages or gates, and sometimes they serve to obstruct the fossé.

8. Gabions are constructed of various sizes. Those which are intended for field works, must be 3 or 4 feet high, and contain 2 or 3 feet in diameter. These gabions are made by means of long stakes, 3 or 4 feet long, which are placed so as to form a circle, which is 2 or 3 feet in diameter. The pickets must be covered and bound in the same manner as hurdles are. Gabions are chiefly of use in embrasures. They are fixed close to each other, and are afterwards filled with earth. There are also gabions of one foot, with 12 inches diameter at the top, and 9 at the bottom. The bank of the parapet is lined with gabions of this construction, behind which troops may be stationed, so as to fire under cover through the intervals. A quantity of large wooden mallets, rammers, hatchets, axes, and grappling irons, is required for this work.

Names of all works used in field FORTIFICATION.

Bridge heads, or têtes de pont, are made of various figures and sizes, sometimes like a redan or ravelin, with or without flanks, sometimes like a horn or crown work, according to the situation of the ground, or to the importance of its defence. Their construction depends on various circumstances; for, should the river be so narrow, that the work may be flanked from the other side, a single redan is sufficient; but when the river is so broad, that the saliant angle cannot be well defended across the river, flanks must be added to the redan; but should a river be 100 toises, or more across, half a square may be made, whose diagonal is the river side; and where the river is from 3 to 500 toises broad, a horn, or crown-work should be made. All the different sorts of heads of bridges, are to be esteemed as good works against a sudden onset only, and their use is almost momentary, as they sometimes serve but for a few days only, and at most during a campaign.

Dams are generally made of earth, but sometimes of other materials, as occasion may require: their use is to confine water.

Flêche a work consisting of two faces, terminating in a saliant angle of 90°, the faces are generally 75, or 80 feet long, the parapet 6 feet thick, and the ditch 7 feet broad.

Forts, in field fortification, are of various sorts, viz.