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on the first vertical column are t'e numbers saliant angle; as likewise all ditches are in expressing the lengths of the exterior sides from general. eighty to 260. In the second, the perpendiculars When the ravelins are made with flanks, as in answering to these sides. In the third, the plate I. fig. 3, the faces should terminate on those lengths of the faces of bastions; and in the of the bastions, at least five toises from the fourth, the lengths of the capitals of the ravelins. shoulders. The flanks are made by setting off
The forts are mostly, if not always, squares : ten toises from the extremities of the faces, from for which reason, the perpendiculars are made f to h, and from m tol; and from the points one-eighth of the exterior sides; because, if they h, l, the flanks h kyl p, are drawn parallel to the were more, the gorges of the bastions would be- capital LO of the ravelin. corne too narrow.
There are sometimes redoubts made in the raIn the little fortification or citadels, chiefly velin, such as in fig. 2, which is done by setting pentagons, the perpendiculars are made one- off sixteen toises from the extremities of the faces seventh of the exterior side. In mean fortifica- on the semi-gorges from N to h, and from JI 10 tion, from any number of sides to an hexagon up- a; and from the points b, a, the faces are drawn' wards is used; and the great is seldom used but parallel to those of the ravelin; the ditch before in an irregular fortification, where there are some the redoubts is six toises, and its counterscarp sides that cannot be made less without much ex- parallel to the faces. pense; or in a town which lies near a great Of Tenailles.-A tenaille is a work made in the river, where the side next the river is made from ditch before the curtains; the parapet is only 200 to 260 toises; and, as that side is less ex- two or three feet higher than the level ground of posed to be attacked than any other, the per- the ravelin. There are three different sorts; the pendicular is made shorter, which saves much first are those, as in fig. 4, which are made in the expense.
direction of the lines of defence, leaving a pasThe faces of the bastions are all two-sevenths of sage of five toises between their extremities and the exterior sides, or nearly so, because the frac- the flanks of the bastions, as likewise another of tions are neglected.
two in the middle for a bridge of communication In general, in all squares, -the perpendicular to the ravelin. is one-eighth of the exterior side, and all penta- The second sort are as those in fig. 5. Their gons one-seventh, and in all the rest upwards faces are in the lines of defence, and sixteen of one-sixth.
toises long, besides the passage of three toises Of the Construction of Orillons and retired between them and the Aanks of the bastion ; Flanks.—Describe the front MPQRST as be- their flanks are found by describing arcs from fore, and divide the flank into three equal parts, one shoulder of the tenaille as centre through the of which suppose Sr to be one; from the op- other, or on which are set ten toises for the flanks posite flanked angle M draw a line Mr, in desired. which take the part mr of five toises; take like- The third sort are those as in fig. 6. Their wise Rn in the line of defence MR, produced faces are sixteen toises, as in the second sort, equal to five toises, and join nm, upon which as and the flanks are parallel to those of the basa base describe the equilateral triangle npm, tions. and from the angle p, opposite to the base as The use of tenailles, in general, is to defend centre, is described the circular flank n m. And the bottom of the ditch by a grazing fire, as likeif Sr be bisected by the perpendicular 1, 2, and wise the level ground of the ravelin, and espeanother be erected upon the face ST, at S, cially the ditch before the redoubt within the the intersection 2 of these two perpendiculars ravelin, which can be defended from no where will be the centre of the arc which forms the else so well as from them. orillon.
The first sort do not defend the ditch so well The orillons are very useful in covering the as the others, as being too oblique a defence; retired flanks, which cannot be seen but directly but, as they are not subject to be enfiladed, M. in the front; and, as these orillons are round, Vauban generally preferred them in the fortifythey cannot be so easily destroyed as they would ing of places, as in the citadel of Lille, at Lanbe if they were of any other figure.
dau, New Brisac, and in many other places. Of the Construction of Ravelins or Half-moons.- The second sort defend the ditch much better Fig. 2. Set off fifty-five toises, from the re-enter- than the first, and add a low flank to those of the ing angle 0 of the counterscarp, on the capital bastions; but, as these flanks are liable to be enOL, or on the perpendicular produced ; and filaded, they have not been much put in practice. from the point L draw lines to the shoulder A B; This defect might however be remedied, by mawhose parts L M, L N, terminated by the coun- king them so as to be covered by the extremities terscarp, will be the faces, and MO, ON, the of the parapets of the opposite ravelins, or by semi-gorges of the ravelin required. This is Mr. some other work. Vauban's method of constructing ravelins, ac- As to the third sort, they have the same adcording to some authors: others say the faces of vantage as the second, and are likewise liable the ravelin should terminate on those of the bas- to the same objections; for which reason, they tions within three toises of the shoulders; which may be used with the same precautions which seems to be the best way, for these ravelins have been mentioned in the second. cover the flanks much better than the others. Tenailles are esteemed so necessary, that there
The ditch before the rarelin is twelve toises, is hardly any place fortified without them; and its counterscarp parallel to the faces of the rave- with reason : for, when the ditch is dry, the part lins, and is made in a circular arc, before the behind the tenailles serves as a place of arms
from which the troops may sally, and destroy the Of Counterguards.-Fig. 10, 11. When the
Counterguards are made before the ravelin on Of Lunettes-Fig. 7, plate I. Lunettes are some particular occasions only; but are freplaced on both sides of the ravelin, such as B, lo quently constructed before the bastions, as coincrease the strength of a place : they are con- vering the flanks wonderfully well. Some austructed by bisecting the faces of the ravelin with thors, as Mr. Blondel and Mr. Coehorn, will the perpendicular LN; on which is set off thirty have them much narrower than they are here. toises from the counterscarp of the ditch, for one Of Horn-works.-Fig. 12, plate I. Produce of its faces; the other face, PN, is found by the capital of the ravelin beyond the saliant making the semi-gorge, TP, of twenty-five angle A, at a distance A B of about eighty toises toises; the ditch before the lunettes is twelve draw D B E at right angles to A B; in which toises, the parapet three, and the rampart eight, take B D, BE, each equal to fifty-five toises; as in the ravelin.
and on the exterior side, D E, trace a front of a There is sometimes anotner work made to co- polygon in the same manner as that of the body ver the saliant angle of the ravelin, such as A, of the place, making the perpendicular B F ten called the bonnet, whose faces are parallel to toises, and the faces thirty. those of the ravelin, and when produced bisect The branches Da, Eb, of the horn-work, when those of the lunettes; the ditch before is ten produced, terminate on the faces of the bastions, toises.
within five toises of the shoulders. The ditch of There are likewise lunettes, such as D in fig. the horn-work is twelve toises, and its counter8, whose faces are drawn perpendicular to those scarp parallel to the branches; and in the front of the ravelin, within a third part from the saliant terminates at the shoulders, in the same manner angle; and their semi-gorges are only twenty as the great ditch before the bastions.
The capital of the ravelin before the front of These kinds of works may make a good de- the horn-work is thirty-five toises, and the faces fence, at no very great cost; for, as they are so terminate on the shoulders, or rather two or near the ravelin, the communication with it is three toises beyond them: and the ditch before
and one cannot well be maintained the ravelin is eight toises. till they are all three taken.
Retrenchments are sometimes made within Of Tenaillons.-- Fig. 9, plate I. Produce the the horn-works, such as S, S; which are confaces of the ravelin beyond the counterscarp of structed by erecting perpendiculars to the faces the ditch, at a distance M N of thirty toises, and of the ravelins, within twenty-five toises of their take on the counterscarp of the great ditch fif- extremities. This retrenchment, like all others, teen toises from the re-entering angle p'to 9, and has a parapet turfed only with a berm of eight draw Ng; then q N Mp will be the tenailles re- feet before it; as likewise a ditch from three to quired; its ditch is twelve toises, that is, the five toises broad. same as that of the ravelin. Sometimes a retired Fig. 13. When a horn-work is made before battery is made in the front of the tenaillons, as the bastion, the distance D L of the front from in B; this battery is ten toises from the front the saliant angle of the bastion is 100 toises, to which it is parallel, and fifteen toises long.
and the branches terninate on the faces of the Retrenchments are commonly made in the adjacent ravelins within five toises from their tenaillons, such as (); their parapets are paral- extremities; all the rest is the same as before. lel to the fronts M N, and bisect the side y N; Of Crown-works. From the saliant angle, A, the ditch before the retrenchment is three toises; fig. 1, plate II. of the ravelin, as a centre, deand there is a banquette before the parapet next scribe an arc of a circle with a radius of about to the ditch of about eight feet, called berm; 120 toises, cutting the capital of the ravelin prowhich serves to prevent the earth of the parapet duced at C; from the point C, set off the cords which seldom has any revetment from falling into CB, C F, each of them equal to 110 toises; and
on each of which, as an exterior side, construct The ravelin, before which tenaillons are con a front of polygon of the same dimensions as in structed, must have its saliant angle much the horn-work; that is, the perpendicular should greater than the former construction makes them; be eighteen toises, the faces thirty, and the otherwise the saliant angles of the tenaillons branches terminate on the faces of the bastions become too acute; for which reason we made within lw y-five toises of the shoulders. the capital of this ravelin forty-five toises, and The ditch is twelve toises, the capital of the the faces terminate within three toises of the ravelins thirty-five, and its ditch eight; that is,
the same as in the horn-work.
Sonetimes the crown-work is made before the like a ravelin, with flanks placed beyond the bastions, as in fig. 2. The arc is described from glacis, such as B; they are made to occupy some the saliant angle A of the bastion, with a radius spot of ground which might be advantageous to of 120 toises as before; and the branches ter- the besiegers; likewise to oblige the enemy ninate on the faces of the adjacent ravelins within open their trenches farther off than they would twenty-five toises of their extremities: the rest do otherwise. The distance from the covert-way of the dimensions and constructions are the same ought not to exceed 120 toises, that it may be as before.
defended hy musket-shot from thence. Horn-works, as well as crown-works, are The gorge, a b, is forty toises; the flanks, ac, never made but when a large spot of ground falls bf, which are perpendicular to the gorge, ten; beyond the fortification, which might be advan- and the faces c d, fd, thirty : the ditch before it tageous to an enemy in a siege, or to cover some is six toises, ending in slopes at both ends; the gate or entrance into a town.
covert-way four; the branches of the covertOf Covert-ways and Glacis.—These are es- way are forty-two toises long, or thereabouts ; teemed some of the most essential parts of a the faces of the places of arms y, y, which are modern fortification ; and it is certain the taking perpendicular to the branches, ten; and the other, the covert-way, when it is in good condition and which is parallel to them, fourteen. well defended, is generally the most bloody ac- The communication from the covert-way into tior of the siege. After having constructed the the redoubt, is five or six toises wide: a traverse body of the place, and all the outworks which is made just at the entrance, and another in the are thought necessary, lines are drawn parallel middle when I is pretty long. The parapets to the utmost counterscarp of the ditches, at six of this communication terminate in a slope or toises distant from it; and the space mn, m n, glacis. included between that line and the counterscarp, If these redoubts are above fifty toises distant will be the covert-way required.
from the covert-way, the besiegers carry their Fig. 3. There is in every re-entering angle trenches round, and enter through the gorge; of the counterscarp a place of arms, m; which by which means the troops that are in them are is found by setting off twenty toises from the re- made prisoners of war, if they do not retire entering and angle a, on both sides from a to b, betimes; to prevent which some other outworks and from a to c: and from the points b c, as should be made to support them. centres, arcs are described with a radius of Of Second Ditches und Covert-ways. — Plate II. twenty-five toises, so as to intersect each other in fig. 4. When the grrund is low, and water to d; then the lines drawn from this intersection be found, there is often a ditch about ten or twelve to the point b, c, will be the faces of the places toises made round the glacis; and opposite to of arms.
the places of arms are constructed lunettes, beIf lines are drawn parallel to the lines which yond the ditch : such as D, whose breadth on terminate the covert-way, and the places of arms, the counterscarp of the ditch is ten toises, from it twenty toises distant from them, the space x, b to a, and from c to d; and the faces a L, d L, S, 7, between these lines and those which termi- are parallel to those of the places of arms; the nate the covert-way, will be the glacis.
ditch before them is from eight to ten toises At the extremities of the places of arms are wide. traverses made, such as v, v, which serve to en- The second covert-way is fuur toises, the semiclose them; these traverses are three toises thick, gorges of the places of arms, m, about fifteeen, and as long as the covert-way is broad, and a and the faces perpendicular to the counterscrap; passage is cut in the glacis round them, of about the second glacis is from fifteen to eighteen toises six or eight feet, in order to have a free commu- broad. This second covert-way has traverses nication with the rest of the covert-way.
every where in the same manner as the first. There are also traverses of the same dimensions Of Profiles.-A profile is the representation before every saliant angle of the bastion and out- of a vertical section of a work; it serves to show works, and are in the same direction as the faces those dimensions which cannot be represented of those works produced ; and the thickness lies in plans, and is necessary in the building of a at the same side as the parapets.
fortification. Profiles are generally constructed The passages round these last traverses are upon thirty feet to an inch. It would be endless likewise from six to eight feet wide.
to describe all their particular dimensions; we In each place of arms are two sally ports, 2,ž, shall, therefore, lay down the principal rules which are ten or twelve feet wide, for the troops only, given by M. Vauban, on this subject. to sally out: in time of a siege they are shut up, 1. Every work ought to be at least six feet with barriers of gates.
higher than that before it, so that it may comOf Arrows and Detached Redoubts.-An arrow mand those before it; that is, that the garrison is a work made before the saliant angles of the may fire from all the works at the same time, glacis, such as A, fig. 3. It is composed of a with great and small arms, at the besiegers in parapet of three toises thick, and forty long; and their aproaches. Several authors, however, obthe ditch before it five toises, terminating in a ject against it. For, say they, if you can discover slope at both ends. The communication from the enemy from all the works, they can discover, the covert-way into these arrows is four or five by the same reason, all the works from their toises wide; and there is a traverse, r, at the batteries; so that they may destroy them withentrance, of three toises thick, with a passage of out being obliged to change their situation, and six or eight feet round it.
thereby dismount all the guns of the place before A detached redoubt is a kind of work much they come near it. But, if all the works were of