ways remained one of the faces of the towers which fronted the field that could not be seen from any other part, the circular form was early preferred. This had also the recommendation of presenting a better resistance to battering engines. Still there remained parts of these towers unseen and incapable of being defended; which caused a second change in their figure, i. e. they made them square as before; but, instead of presenting a face to the field as formerly, they presented an angle, the origin of our modern bastion; and thus was effected such a disposition of the works, that no part could be attacked without being seen or defended from some other part. Ditches were added; and thus remained long stationary the art of fortification: indeed until the invention of that terrible assailant gunpowder. This entirely changed the mode of attack, and by consequence that of defence.

In the history of fortification we find this obvious division, and we need not take back the modern reader beyond the period of this cele

brated invention.

When the besiegers began regularly to use artillery, it became requisite that the besieged should also employ it; and, to furnish room for this, a rampart was first raised behind and close to the main wall of fortresses: the towers were enlarged; and the smaller walls were thickened by parapets of earth behind, so as to secure the besieged from the fire of the enemy.

For a length of time fortified towns were placed, by these means, in a situation to take their full advantage of the new art of war. Sieges were by no means diminished in their ordinary length: a wall of Magdebourg is recorded to have received 1550 cannon-shot, in the early part of the seventeenth century, without injury to it. If the siege of an important place was not early successful, it generally terminated in the loss of the major part of those who assaulted it.

But the great modern proficient in this art, M. Vauban, now appeared, and effected at the end of the seventeenth century a complete revolution in it. He invented a method of attack, against which no mode of defence hitherto adopted has been able finally to stand; and though, during the latter part of his life, he applied his great talents also to a system of defence, upon which Coehorn, Cormontaingne, and others as we shall see have improved, nothing has as yet fully counteracted the mode of ricochet firing introduced by this celebrated commander at the siege of Ath. We shall not fail, in the sketch of this art that follows, to include every principal suggestion that has been made on this subject, and, among others, the plan of M. Carnot, so justly celebrated for his mathematical skill and military talents. But we have completely satisfied ourselves that the vertical fire on which he mainly relies is a chimera.

Modern fortification treats of the plan of defence now used, i. e. turning the walls into ramparts, and square and round towers into bastions, defended by numerous outworks; all which are made so solid that they cannot be beaten down, but by the continual fire of batteries. These bastions at first were small, and at a great dis

tance from each other, as are those still to be seen at Antwerp, their gorges narrow, and their flanks and faces short. For the invariable practice then, and for some time after the introduction of them, was to attack the curtains and not the faces of the bastions. But since that time they have been considerably improved and enlarged, and are now arrived to that degree of strength, that it has been a received opinion, that the art of fortification is at its height, and incapable of being carried to greater perfection. This, however, Mr. Glenie, p. 9, Military Construction, disputes, and M. Carnot seemed resolved, a few years since, to confirm his opinions as to all past methods.

Offensive fortification is a term improperly applied to the besieging and taking fortified places; it is said further to teach a general how to take all advantages for his troops; the manner of encamping, and method of carrying on either a regular or irregular siege, according as circumstances may direct. It may with much greater propriety be called the war of sieges. See SIEGES.

Fortification has been sometimes treated of under the terms regular and irregular.

Regular fortification is that which is erected according to the rules of art, and is particularly applied to a construction made from a figure or polygon, which has all its sides and angles equal. The flanked or salient angles in such a fortification are equal to one another, equally distant from one another, and are each of them at the distance of about that of serious musket shot from the flanks which defend it. For an irregular fortification having the flanked angles, as also the flanks and lines of defence, unequal, may be constructed from the sides of a regular polygon, as well as from those of an irregular polygon, by drawing the perpendiculars to the regular polygon from points different from those of their bisections. See Glenie's General Rule for Irregular Construction.

Irregular fortification, on the contrary, is that where the sides and angles are not uniform, equi-distant, or equal; which is owing to the irregularity of the ground, valleys, rivers, hills, &c.

Most fortifications are a mixture of regular and irregular works. The position of waters, hills, and other principal geographical features of a site of ground, previous plans adopted, and various other considerations induce the ablest engineer to be content with arriving only at the utmost practical regularity. In this article, therefore, we shall pursue the main divisions of permanent and field fortification, as embracing all the principal topics we need discuss; and shall present under each a brief sketch of the most approved systems from that of M. Vauban downwards. We shall subjoin a few observations on the mode of attacking fortified places.

PART I.

OF PERMANENT FORTIFICATIONS. SECT. I.-M. VAUBAN'S FIRST SYSTEM. M. Vauban was clearly indebted to his predecessor in this art, the count de Pagan, for his general definitions and dispositions, especially in his first

in the first vertical column are the numbers expressing the lengths of the exterior sides from eighty to 260. In the second, the perpendiculars answering to these sides. In the third, the lengths of the faces of bastions; and in the fourth, the lengths of the capitals of the ravelins. The forts are mostly, if not always, squares: for which reason, the perpendiculars are made one-eighth of the exterior sides; because, if they were more, the gorges of the bastions would be

come too narrow.

In the little fortification or citadels, chiefly pentagons, the perpendiculars are made oneseventh of the exterior side. In mean fortification, from any number of sides to an hexagon upwards is used; and the great is seldom used but in an irregular fortification, where there are some sides that cannot be made less without much expense; or in a town which lies near a great river, where the side next the river is made from 200 to 260 toises; and, as that side is less exposed to be attacked than any other, the perpendicular is made shorter, which saves much expense.

The faces of the bastions are all two-sevenths of the exterior sides, or nearly so, because the fractions are neglected.

In general, in all squares, the perpendicular is one-eighth of the exterior side, and all pentagons one-seventh, and in all the rest upwards of one-sixth.

Of the Construction of Orillons and retired Flanks.-Describe the front MPQRST as before, and divide the flank into three equal parts, of which suppose Sr to be one; from the opposite flanked angle M draw a line Mr, in which take the part mr of five toises; take likewise Rn in the line of defence M R, produced equal to five toises, and join nm, upon which as a base describe the equilateral triangle npm, and from the angle p, opposite to the base as centre, is described the circular flank nm. And if Sr be bisected by the perpendicular 1, 2, and another be erected upon the face ST, at S, the intersection 2 of these two perpendiculars will be the centre of the arc which forms the orillon.

The orillons are very useful in covering the retired flanks, which cannot be seen but directly in the front; and, as these orillons are round, they cannot be so easily destroyed as they would be if they were of any other figure.

Of the Construction of Ravelins or Half-moons.Fig. 2. Set off fifty-five toises, from the re-entering angle O of the counterscarp, on the capital OL, or on the perpendicular produced; and from the point L draw lines to the shoulder A B; whose parts LM, LN, terminated by the counterscarp, will be the faces, and MO, ON, the semi-gorges of the ravelin required. This is Mr. Vauban's method of constructing ravelins, according to some authors: others say the faces of the ravelin should terminate on those of the bastions within three toises of the shoulders; which seems to be the best way, for these ravelins cover the flanks much better than the others.

The ditch before the ravelin is twelve toises, its counterscarp parallel to the faces of the ravelins, and is made in a circular arc, before the

saliant angle; as likewise all ditches are in general.

When the ravelins are made with flanks, as in plate I. fig. 3, the faces should terminate on those of the bastions, at least five toises from the shoulders. The flanks are made by setting off ten toises from the extremities of the faces, from fto h, and from m to l; and from the points h, l, the flanks h k,l p, are drawn parallel to the capital LO of the ravelin.

There are sometimes redoubts made in the ravelin, such as in fig. 2, which is done by setting off sixteen toises from the extremities of the faces on the semi-gorges from N to h, and from M to a; and from the points b, a, the faces are drawn parallel to those of the ravelin; the ditch before the redoubts is six toises, and its counterscarp parallel to the faces.

Of Tenailles.-A tenaille is a work made in the ditch before the curtains; the parapet is only two or three feet higher than the level ground of the ravelin. There are three different sorts; the first are those, as in fig. 4, which are made in the direction of the lines of defence, leaving a passage of five toises between their extremities and the flanks of the bastions, as likewise another of two in the middle for a bridge of communication to the ravelin.

The second sort are as those in fig. 5. Their faces are in the lines of defence, and sixteen toises long, besides the passage of three toises between them and the flanks of the bastion; their flanks are found by describing arcs from one shoulder of the tenaille as centre through the other, or on which are set ten toises for the flanks desired.

The third sort are those as in fig. 6. Their faces are sixteen toises, as in the second sort, and the flanks are parallel to those of the bastions.

The use of tenailles, in general, is to defend the bottom of the ditch by a grazing fire, as likewise the level ground of the ravelin, and especially the ditch before the redoubt within the ravelin, which can be defended from no where else so well as from them.

The first sort do not defend the ditch so well as the others, as being too oblique a defence; but, as they are not subject to be enfiladed, M. Vauban generally preferred them in the fortifying of places, as in the citadel of Lille, at Landau, New Brisac, and in many other places.

The second sort defend the ditch much better than the first, and add a low flank to those of the bastions; but, as these flanks are liable to be enfiladed, they have not been much put in practice. This defect might however be remedied, by making them so as to be covered by the extremities of the parapets of the opposite ravelins, or by

some other work.

As to the third sort, they have the same advantage as the second, and are likewise liable to the same objections; for which reason, they may be used with the same precautions which have been mentioned in the second.

Tenailles are esteemed so necessary, that there is hardly any place fortified without them; and with reason for, when the ditch is dry, the part behind the tenailles serves as a place of arms