ter and Landau, on the Rhine frontier, Taban introduced marked changes

if astriction; and these were carried still 3riac, about the end of the century. The Mos al Tauban's 2d and 3d systems have been

deduced from these works. The characteristic of both is a polygonal enceinte, flanked by small casemated towers, or bastionettes, and these covered by detached bastions. At New Brisac, (3d system,) Vauban also greatly enlarged both bastion and ravelin, placing a strong redoubt, or inner work, in the latter.

After Vauban, the next great engineer who devoted himself to the advancement of the art, was Cormontaingne.*

What is usually taught under the name of the Modern System is mainly based on the improvements of Cormontaingne, modified by subsequent French engineers. Its main features of difference from the first trace of Vauban are,

1st, The enlargement of the bastions, affording more space for artillery, musketry, the defence of breaches, and the construction of retrenchments on those works which are at once the most active in defence and the most liable to attack.

2d, The great salience and capacity of the ravelins, compelling the attack and capture of those works before the crowning of the covered-way in front of the bastion can be accomplished. This is not necessarily the case in Vauban's system, where the salients of bastion and ravelin are nearly included in the circumference of the same circle. Vauban's ravelin compels the besieger to use more means, for it must be reduced; but this need not be till all is ready for the attack of the bastion also, and therefore it adds little or nothing to the duration of the siege. In the modern system, also, the ravelin completely covers the shoulders of the bastions from batteries on the glacis before it. In Vauban, these batteries can breach the bastion so near the shoulder that the flanks are thrown open to enfilade. The salience of the ravelins, likewise, compels the besieger to open his first parallel at a distance too great for the effective ricochet of the faces of the bastions, and gives great protection to sorties.

3d, The ample size of the ravelins admits of the construction of redoubts within them, which must also fall before the bastion can be carried, their flanks bearing in reverse fire upon the breaches.

* See NOTE V, Cormontaingne.

4th, The construction of redoubts within the spacious reentering places of arms, which, in combination with retrenchments across the adjoining rampart of the ravelin, still further retard the completion of the crowning lodgments before the bastion. Thus five works must be captured before the breaching batteries against the bastion can be established.*

The revetments in this system are what is termed countersloping; that is to say, they are perpendicular on the outer side, and on the inner side expand towards the base. This expansion, instead of being made in a slope, is usually gained by a succession of steps or offsets. Demi-revetments are those employed, and a rectangular tablette takes the place of the rounded cordon, the upper side of which forms a sort of small berm, 2 in width, between the foot of the exterior slope and the face of the wall. The counterforts are rectangular in plan. Sometimes the revetments are constructed en décharge—that is, with arches and backwalls between the counterforts. Doorways being left through the latter, thus galleries are formed behind the wall, from which, by loopholes, a fire may be brought on the ditches.

The main advantages of the modern system, from the salience of the ravelins, &c., will not be developed on a figure lower than the octagon.

Construction.t-The length of the yards;‡ the perpendicular, as before, is

exterior side is 384 of this length.

The face of the bastion is of the exterior side, and the flanks are drawn perpendicular to the lines of defence. The rounding of the main ditch before the bastion is described as before, but the tangents which define the remainder of the counterscarp are drawn from the crest of the parapet at the shoulders of the bastions, not from the shoulder angle of the cordon.

The tenaille is 16 yards thick as before, but its ends, as well as its gorge, are 11 yards from the escarp of the enceinte. The crest of the parapet forms on each side a return or small

* Viz., two ravelins and the redoubt in one of them at least, and the redoubts in the two places of arms.

+ See Plate VIII., fig. 120.

Equal nearly to 360 toises. See note, p. 85.

flank perpendicular to a line drawn from the middle of the ditch of the Ravelin, at its intersection with the originally traced main counterscarp.

To construct the Ravelin.-Set off on the face of each bastion a distance of 36 yards from the shoulder. On the imaginary line joining these points construct an equilateral triangle. The apex of the triangle will be the salient of the Ravelin; its faces terminating, as in the former system, on the counterscarp as originally traced. The ditch of the Ravelin, and the Covered-way are traced as before; the latter 11 yards wide.

The faces of the Redoubt in the ravelin are parallel to those of the Ravelin, being directed on the crest of the parapet at the shoulders of the bastions. The counterscarp of the ditch of the redoubt is parallel to these faces, the breadth of the ditch being 11 yards.

To draw the Flanks of the Redoubt.-From the intersection of the face, with the originally drawn counterscarp of the main ditch, set off 11 yards along the latter line, and 18 yards along the face. The line joining the two points so found will be the flank of the redoubt. The gorge of the redoubt will be a line joining the extremities of the crest of these flanks. The gorge of the ravelin is drawn parallel to the exterior side, 6 feet within it, to meet the flanks of the redoubt on each side.

To construct the Redoubt in the re-entering Place of Arms.— Draw its capital, bisecting the re-entering angle of the counterscarp before each face of the bastion. A line drawn from the salient of the bastion to the salient of the ravelin, intersecting this capital, will give the counterscarp of one face of the redoubt. A line drawn from the angle of the salient place of arms, through this intersection, will give the counterscarp of the other face. The escarps are parallel to these counterscarps, with a ditch of 6 yards wide between. A small flank is given to the redoubt on the side towards the ravelin, by making the crest only of the parapet, for a length of 6 yards, perpendicular to a line drawn from its extremity to the salient of the ravelin. By the prolongation of this latter line a

mangular portion is cut from the interior of the redoubt, and uted a he fan of the ravelin.

The men of the re-entering place of arms is circular. The are a teserien fem the original angle of the counterscarp Corment je he finenes before ravelin and bastion as a centre, lassing brough point in the capital of the redoubt, 20 yards

jeand be countersear.

Traverses it each intersection of this are with the outer aze the covered-way complete the enclosure of the places There are three more traverses on each branch of the 'overed-way of the cavelin, the outermost terminating on the prolongations of the faces of that work. These last traverses have superior slopes of only 9 feet; those adjoining the place of arms being 18. The passages round the traverses are en crematture, or indented. The breadth of the glacis is 60 yards. At the salient place of arms before the ravelin, the angie of the crest of the giacis is cut off by a line 9 yards long at right angles to the capital.

There is a coupure, or retrenchment-cut, across the rampart of each face of the ravelin. It consists of a parapet, and a ditch 3 yards wide, the counterscarp of which is determined by a perpendicular to the face of the ravelin drawn from the extremity of the escarp of the redoubt in the place of

arms.

The principal advantages sought by this trace have been aiready pointed out. A few of the minor peculiarities may be noticed. The trouée of the Tenaille, being masqued by the spread of the ravelin, the ends of the Tenaille may be removed to a safer distance, as regards splinters, &c., from the flanks, without fear of exposing the curtain to the enemy's lodgments on the glacis. The small flanks given to the parapet of this work serve to bring a musketry fire directly on an enemy outering the main ditch from that of the ravelin.

The ravelin being traced as an equilateral triangle has an ening of 60° only, the most acute which is permitted by the

t' experience. When several fronts of this system are ne, this great salience of the ravelins completely covers 4 of the bastions from enfilade.