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Behind the lower parapet there is a banquette of three feet, and a rampart of five; and under this rampart a stone gallery, which runs from one end to the other, and is divided into several apartments, which are shut with doors; as likewise another, going from the saliant angle of the lower faces, to that of the higher, with loop-holes from distance to distance facing the dry ditch; there is likewise a row of palisades placed parallel to the higher faces, and at four toises distant from them.

2

There are three embrasures in Or, as has been said, to flank the ditch & behind the towers; and two in I() to'flank the dry ditch near the higher faces.

The great ditch is twenty-four toises broad; and its counterscarp parallel to the lower faces of the bastions; the semi-gorges ( L of the ravelin are twenty-nine toises, and the faces LP, forty-five; the dry ditch Y is sixteen toises, the rampart twenty-eight feet, and the lower faces a Tare parallel to the higher ones; the parapet of which is twenty and the banquette three.

The level ground of the rampart in the ravelin near the saliant angle is twenty feet broad, for the length of twenty toises from that angle, and the rest but fifteen.

In the gorge of the ravelin is a small redoubt a, of about five feet high, and underneath a lodgment of stones, the walls being eighteen inches thick at the sides; the roof is made of planks, with three feet of earth over them.

There is a dry ditch going from the extremities of the faces to the redoubt, and round its angle, having a row of palisades before it, to secure the retreat from the ravelin into this redoubt; there is likewise another row going from the extremities of the faces, in a round form, turning towards the gorge of the ravelin.

In the dry ditch of the ravelin, within six toises from the great ditch, is a coffer, and a ditch p of six toises before it: this coffer has a wall on both sides, and the roof is planked and covered with a foot and a half of earth; above this is a stone parapet of five feet high, with a banquette behind it.

There runs a covered gallery under the rampart of the lower faces, and another joining the two saliant angles, together with a row of palisades, in the same manner as in the dry ditch be

fore the bastions.

The wet ditch before the ravelin is eighteen toises; the counterguards r, which the author calls cover-faces, are twenty-five feet broad, and the ditch before them fourteen toises; the covertway is twelve toises broad, and the glacis twenty; the semi-gorges fg,gh, of the places of arms, are twenty-two toises, and are taken from the point , where the branches of the covert-way meet, and the faces fk, hk, are twenty-eight; within these places of arms are traverses of twenty feet thick and eighteen toises long, within ten or twelve feet from, and parallel to the faces.

The stone lodgments b, within the places of arms, are found by setting off twelve toises from the point g, for the semi-gorges, and the faces are drawn parallel to those of the places

of arms.

At six toises from the places of arms are

coffers q of eight feet broad, made with planks at the sides, and above with a foot of earth over and before them.

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There are two banquettes all round the covert way, and before the traverses; as also two rows of palisades before the traverses, one of which joins them, and the other goes round the covertway.

Lastly, the re-entering angles of the counterscarp next to the covert-way are made a littie round as likewise that in the ravelin: but the contrary way, that is, they are made hollow.

His Second System he adapts to a heptagon whose interior side is 126 toises, and the level of the ground to be three feet above the surface of the water.

Let, therefore, the interior side, AB plate IV. fig. 3, of an heptagon be 126 toises; take in the capitals, AC, BD, each of seventy-two toises; at the extremities C, D, make the angles ACE, BDF, each of forty degrees; and set off sixtysix toises for the faces CE, DF, of the bastions; on the interior side, take AG, BH, each of thirty toises, and from the point D, as centre, describe an arc through the point G, on which set off a chord of thirty; and on this chord describe the mean flank GI, which is an arc of sixty degrees.

Draw a line from the saliant angle D through the extremity I of this flank, on which take I a of ten toises; join a E, on which describe the orillon as usual.

The outline of the higher flank is thirteen toises distant from that of the outline of the mean; this flank is an arc described from the the same centre as that of the former, the chord of which is forty toises.

From the points G, H, draw the broken parts of the curtain, perpendicular to the capital of the bastion, and make it nine toises long; the extremity of the higher flank is terminated by the inside line of the parapet of the curtain produced.

The tenaille is found by producing the faces of the bastions ten toises; through the extremity of which an arc is described from the opposite saliant angle of the bastion, as centre; on this arc is set off a chord of twenty toises; and this chord serves to describe the flank, upon which is an arc of sixty degrees; the curtain is a right line.

There is a wet ditch before the tenailles of en toises broad, with two bridges at each end, near the orillons; the one directly over it, and the other along the faces of the bastion.

The dry ditch round the body of the place is twenty toises broad, before the faces of the bastion to which it is parallel, and the lower rampart, K L, twenty-nine feet; the semi-gorges M L are fifteen toises, and the flanks LN eigh ten, and are described from the saliant angles K of the lower faces as centres.

The saliant angle of the ravelin is 125 toises distant from the curtain of the body of the place, and is seventy degrees; the faces are fifty toises long; the faces of the redoubt r are sixteen toises distant from those of the ravelin, and fourteen long.

The wet ditch round the lower faces of the ravelin is twenty-four toises broad: the work be

yond this ditch, which the author calls the second counterscarp, is twenty, parallel to the ditch.

To find the broken part of this work, join the two re-entering angles, m,r; on which take mr of thirty toises, and draw r t, r v, parallel to the outline of the counterscarp, each equal to twelve; set off twenty-two from t to s, and from v to q; and upon these lines as chords describe the round flanks, which are arcs of sixty degrees.

The traverses in this counterscarp are drawn at ten toises from the flanks perpendicular to the parapet.

The redoubt x, in the re-entering angles, are found by setting off sixteen toises from the points m to n, for their capitals, and the faces are parallel to the broken curtain before them; those marked y, which are in the saliant angles, are found by producing the counterscarps of the great ditch, and setting off twelve toises from the points of their intersections for their faces; and the flanks are drawn parallel to their capitals.

The ditch before this work is fourteen toises; as to the covert-way and glacis, they are the same as in the author's first method.

Coehorn applies his third system to an octagon, and supposes the level of the water to be five feet below the horizontal ground. The exterior works of this system, that is, the detached bastions and the counterguards, ravelins, covertways, &c., alone present the same arrangement as that of the whole first system; with the exception, however, that independently of the detached bastions being not joined together by any curtains, they only have double flanks instead of treble ones. Each of these bastions also has a redoubt at its gorge, with a dry ditch in front and a crenelled gallery adapted to the counterscarp of this ditch. There is likewise a dry ditch before the redoubt at the gorge of every capital ravelin, which ditch is connected with the faces of the ravelin, as the dotted lines show, by means of coupures made in the direction of the coffers between the capital and the lower ravelins, or nearly in that direction. Besides, in addition to the coffers in front of the re-entering places of arms, Coehorn constructs a crenelled gallery along the faces of these works, on which account the palisades in this part of the covert-way are to be two toises distant from the crest of the glacis.

Behind the exterior works above mentioned is the body of the place, consisting of bastions with common orillons, a revetment, and double flanks. The curtains which connect the lower flanks are broken as in the first system, and at each of their extremities, between them and the principal curtains, a kind of harbour is constructed, by means of which, as well as of vaulted passages made under the lower curtains, the garrison is able to keep up a communication with the exterior works. There is also a kind of circular harbour at the gorge of these works.

Some of Coehorn's dispositions in his third system are certainly not below the high reputation of such an eminent engineer; but, independently of the great labor and quantity of masonry which this system requires, the communications with the exterior works, across wet ditches, are

difficult; the arrangement of the system in question also has the inconvenience of occasioning several openings to be left, through which the besieger can see the exterior works and the body of the place from the crowning of the covert-way. Therefore, all engineers coincide in their opinion that it is inferior to the first system, and consequently to the second.

We shall not therefore detain the reader by a more particular description of it.

SECT. IV.-CORMONTAINGNE'S SYSTEM. This is, in fact, with some modifications, the modern bastion system of fortification. Upon Vauban's first or general system, this able engineer suggested the improvement, first of a much greater projection which he allowed to the ravelins, whereby he considerably augmented their action upon the attacks. Secondly, of constructing the ravelins without flanks, and directing their faces to a smaller distance from the flanked angles of the bastions, by which he covered the shoulders of these works still more effectually than Vauban had done, as well as the curtains, and the openings between the flanks of the bastions and the profiles of the tenailles. Thirdly, Cormontaingne's redoubts in the ravelins are better contrived than those of Vauban, and answer purposes much more important; whilst the larger size of his re-entering places of arms renders them also more beneficial to the defence, and particularly on account of their substantial redoubts, which, besides the other material advantages derived from them, have their faces so disposed as to secure them from enfilade, and allow their fire to have a direction close and nearly parallel to the prolongations of the capitals. This advantage, which none of Vauban's systems afford, is so much more important as the besieger generally advances in the direction of the capitals. Cormontaingne likewise concealed the masonry of all the revetments of the place from the view of the besieger previous to his gaining the glacis, and thereby secured it from the fire of his more distant batteries. Lastly, this engineer much improved the communications, although not to such a degree as would be requisite for attacking the besieger to advantage, in the works which he may have taken so as to drive him out of them.

Independently of the above improvements which Cormontaingne has made in Vauban's First System, he also illustrated the superior properties that a fortification acquires, from the exterior sides of the fronts which compose it either forming very obtuse angles with each other, or being all in the same straight line.

To describe Cormontaingne's system, with such alterations as have been since suggested and are at present most generally adopted, proceed as follows::

The length of the exterior side being at least 130 toises, but not exceeding 180 toises, construct the bastions and curtains as in Vauban's First System: with the exception, however, that the length of the faces AC and BD (plate V.) of the bastions is to be one-third of the exterior side, and the direction of the flanks perpendicular to the lines of defence. It is here supposed

that the polygon is at least a hexagon; but in the square and the pentagon, the length of the faces should not exceed two-sevenths of the exterior side, so that the flanks may be sufficiently long. To construct the tenaille draw bc and HI parallel to the curtain, bc being five toises distant from it, and HI from twelve to thirteen toises, according to the length of the flanks of the bastions; and if, after making Ga and K d parallel to these flanks, with an interval of five toises between them, ab and c d are drawn parallel to GH and IK, at a distance from them equal to that between be and HI, the tenaille will be completed. Its nearest extremities to the shoulders of the bastions may be rounded off, and the interior side of the parapet broken for a length ef of about three toises, as the figure shows.

The principal ditch is fifteen toises broad opposite the flanked angles of the bastions; but may be made narrower to advantage, provided a proper depth can be allowed to it, as well as such a direction to the superior slope of the parapet of the bastions as will render the fire of the faces effectual upon the counterscarp in front.

Set off fifteen toises from C to g, as well as from D to h, and, supposing g and h to be joined by a line, construct upon it the equilateral trian gle g Mh, so as to have the principal line of the faces ML and MN of the ravelin; then draw Pk and P parallel to these faces, directing them towards the interior meeting i of the pa rapet of the face and the flank of the bastion contiguous to them, and they will give the direction of the principal line of the faces of the redoubt.

The gorge of the ravelin and its redoubt is to be determined by means of drawing, from the flanked angle of each collateral bastion, a line Bmn passing through the extremity m of the opposite face of the ravelin; that is, of the interior side of the parapet. In this manner, the gorge will be entirely secured from the fire which the besieger might otherwise direct upon it from the crowning of the saliant places of arms in front of the bastions.

In respect to the flanks of the redoubt of the ravelin,-from g, where the principal line of the face ML of the ravelin meets the face of the bastion, draw an indefinite line through the intersection k of P k and the gorge of the redoubt; and, after setting off six toises and a half from k to q upon this line, describe the flank Op forming with gq the angle gq 0 of 100 degrees.

The ditch of the ravelin is nine or ten toises broad, and that of the redoubt five toises; the counterscarp of both these works is parallel to their faces, excepting that part in front of the saliants which is made circular: the breadth of the covert-way is five toises.

To describe the re-entering places of arms, measure off five or six toises from r to s, upon the interior side of the parapet of the face of the bastion; and from s draw the indefinite line su, making with rs an angle of 100 degrees; take the distance vt, from the angle v to the intersectiont of su and the counterscarp, and set it off from v to w; then draw wu forming the same an

gle with the counterscarp of the ravelin, as tu with that of the bastion; and such parts of wu and tu as project beyond the covert-way will give the faces of the re-entering place of arms, allowing for the passages between the two contiguous traverses and the glacis.

For the redoubt of the re-entering place of arms, set off eleven toises upon the counterscarp rom t to r and from w to; as well as seven toises and a halt from a to b', and from c' to ď, upon the collateral branches of the covert-way. Then draw the interior side rg'z of the parapet of the faces, in the direction of zb' and zd, and cut off part of g'z in order to describe the small flank f'e', the length of which should be three and a half or four toises, and its direction such as to allow it to see in reverse the breach of the ravelin. The escarp and counterscarp of the redoubt are to be made parallel to the faces, three toises being allowed for the breadth of the ditch; whilst its gorge, on the side next to the contiguous ravelin, should terminate upon the line M drawn from the saliant of this work through the extremity e' of the flank f'e', so as not to be exposed to the fire of the besieger from the crowning of the saliant place of arms in front of the ravelin.

Eighteen feet are allowed for the thickness of the traverses at the re-entering places of arms; but those at the saliant places of arms, as well as the intermediate traverses, are only nine feet thick, the breadth of the passages between the latter and the counterscarp being six feet.

In regulating the inclination of any glacis, care should be taken that its superior surface, being indefinitely produced towards the works behind, may not pass above any of their lower lines of fire, which are those of the artillery. Therefore, this inclination depends upon the command of the said works, as well as upon their distance from the crest of the glacis; but, in general circumstances, it is regulated at the rate of about three inches to each toise of the breadth of the glacis.

It is materially important that the glacis should have a proper inclination; for, if it be too steep, the great depression which the fire of the garrison should have, in order to defend it will render this fire ineffectual; and if, on the contrary, the inclination of the glacis is too little, the besieger's cavaliers of trenches will only require a small height; on which account they will be less liable to be destroyed by the artillery of the place. Cavaliers of trenches are works which the besieger constructs upon the glacis, for the purpose of raising the troops who occupy them, so that these troops may plunge their fire into the

covert-way.

Passages c (plate VI. fig. 1) called sally-ports, are cut in the glacis, which, as their name indicates, serve for the sallies; they form ramps twelve feet wide, having a gentle slope, so as to allow artillery and cavalry to pass conveniently through them. A curved direction is requisite for these ramps, because, if they were straight, the besieger would enfidale them, and destroy the double barriers that the garrison places across them, in the direction of the crest of the glacis. for the purpose of securing the opening into th

covert-way, which they occasion, whilst the covert-way opposite this opening would also be much exposed. The sally ports are to be placed in the faces of the re-entering places of arms, and in the branches of the covert-way of the ravelins between the second and third traverses, as these situations will allow the sallies to be effectually protected in their retreat by the saliants of the covert-way of both the bastions and ravelins. Besides the sally-ports will be better secured than if they were in the saliant places of arms, or near them. In those parts of the fortifications where a road d is made across the glacis, in order to communicate with the country, it is commonly placed between the traverse of a re-entering place of arms (on the side towards the ravelin) and the contiguous traverse of the covert-way of the ravelin. The road is made winding, and from eighteen to twenty or twentyone feet are generally allowed for its breadth, the profile of the glacis on each side being supported by a wall.

Supposing to be the middle of that end of the sally-port (fig. 2, plate VI.), which is in the direction of the crest of the glacis, erect at a, the, perpendicular ab to that crest, and make it equal to eighteen feet, or any other dimension which the requisite length of the sally-port, according to the greater or smaller elevation of the glacis above the covert-way, may render necessary. Set off one toise from a to b, as well as from a to c, for the breadth of the sally-port, and from c and bas centres, with cb as a radius, describe arcs, cutting each other in e; then from e describe the arc c b. Make cf equal to the base of the interior slope of the glacis, or a little longer, and describe from ƒ and bas centres, with fb as a radius, arcs intersecting at g, from which point, as a centre, the arc fb is to be described. In respect to the other profile of the sally-port, make d h equal to ad, and erect the perpendicular hi of the same length as a b. Next, from d and i as centres, with di as a radius, describe arcs intersecting at m, and m describe the arc di; set off the length of cf from d to n, and from n and i as centres, with ni as a radius, describe arcs cutting each other in o; then from o as a centre, describe the arc 'n i.

On the subject of the communications of this system, an able commentator upon it, colonel de Malortie, observes, the gates should as much as possible be placed on the least exposed fronts, as this situation will not only render them more secure, but allow sallies to be conveniently made, consisting either of cavalry or infantry, in order to attack in flank and in reverse the besieger's approaches towards some of the other fronts; and, whenever fronts having gates are liable to be attacked, it is proper that they should be flanked by works inaccessible to the besieger. Those parts of the principal roads leading to the gates, which are beyond the glacis, should also be enfiladed by the artillery of the place, so that they may not serve for any purposes useful to the enemy.

The gates nearest to the town are those which belong to the body of the place, and lead to the bridges constructed across the principal ditch, in order to gain the gorges of the redoubts in the

opposite ravelins. These gates should be placed in the middle of the curtains, this part of the fortification being the best covered, and the least exposed to be breached; and they have a bombproof archway, which, at the exterior opening, is twelve feet high in the clear, or a little more, and about ten feet broad; wider spaces are contrived inside of it, from distance to distance, where people on foot may retire when any carriage happens to pass. The exterior of the entrances into the gateways generally has ornaments of masonry, but the architecture should be simple, as any superfluous decorations would augment the expense, without answering any useful purpose; and it is also to be observed, that the masonry should not be carried up higher than the top of the parapet, since, otherwise, it would become a mark for the besieger's artillery: nor should any buildings be constructed over the archway, although this has been formerly done.

In respect to the standing bridges they may be constructed wholly with stone, when the fronts where they are situated are neither liable to be attacked, or much exposed to the effect of the besieger's shells; provision should, however, be made, in two of the central piles, for placing a few mines to blow up the bridge, if, on account of any unexpected circumstances, it should become instantly necessary to destroy the communication. But it is preferable, under all suppositions, that the bridges should be so contrived as to allow them to be speedily taken to pieces, without encumbering the ditch with rubbish. In consequence, the upper part of the bridges should consist of timber, and be supported by piles of masonry fifteen feet distant from each other, from centre to centre. The length of the draw-bridges is in general twelve feet, and their breadth eleven feet.

From the redoubt of the ravelin, a gate constructed in one of its faces, with a bridge across the ditch in front, leads to the terreplein of the opposite face of the ravelin; whence another gate, also preceded by a bridge which is thrown across the ditch of the ravelin, serves to communicate with the covert-way, and from this work with the road cut through the 'glacis. But neither of these gateways is arched over, and each consists of an uncovered passage made through the rampart, the profile on each side being supported by a wall in which recesses are contrived for the security of people on foot, if any carriage should happen to pass.

The proper situations for the ramps depend on the nature of the works, and the localities; th are generally placed in the middle of the curtains at the gorges of cavaliers and full bastions, in the flanks and faces of empty bastions, in the faces of out-works, in barbet batteries, &c. short, wherever this kind of communication may be usefully employed.

In

The arrangement of the posterns of each front is as follows: there is a postern underneath the curtain, which serves to communicate from the place with the principal ditch; and, when this ditch is dry, another postern is made under the tenaille, leading to the caponier in front. The communication from the redoubt of the ravelia

FORTIFICATION.

with its own ditch takes place by means of a postern situated under each flank, near the angle of the shoulder; and the redoubts of the re-entering places of arms have each two posterns forming the communication from the redoubt with its ditch.

Before explaining the usual distribution of the pas de souris, it is necessary that the following remarks, relating to the ditches and other objects should be premised.

When the principal ditch contains water, or is dry but very deep, a smaller depth is allowed to the ditch of the ravelin, as in both circumstances this ditch will be better seen from the faces of the bastions which flank it, and therefore more effectually defended; whilst, if the principal ditch is wet, that of the ravelin will be kept dry, which is another advantage.

The ditch of the redoubt in the ravelin is made less deep than that of the ravelin, so as to impede the besieger in his attempt to penetrate into it from the principal ditch, after gaining this ditch through that of the ravelin, in order to cut And, off the troops which defend the ravelin. as a further precaution for the security of these troops in their retreat, the ditch of the redoubt is sunk a little deeper opposite the flanks than along the faces, besides being covered by halfcaponiers U, which, in addition to the coupures X in the ravelin, deprive the besieger of the means of plunging his fire, from the terreplein of the ravelin, into those parts of the ditch of the redoubt where the posterns are placed. Another advantage that is derived from allowing a smaller depth to this ditch than to the ditch of the ravelin, is to render more effectual the flanking defence which it receives from the faces of the

bastions.

The ditch of the redoubts in the re-entering places of arms is still less deep than that of the redoubt in the ravelin, by which means its flanking defence from the bastion on one side, and the ravelin on the other, is improved. It has no communication with the ditch of the ravelin, so that the besieger cannot penetrate into it from this ditch. The manner in which the pas de souris are generally distributed shall now be explained.

A double pas de souris is placed in the middle of the gorge of the tenaille, in order to mount upon its terreplein, and there is a double one also at the gorge of the redoubt of the ravelin, which serves to get up to the plane of site, whence the terreplein of this redoubt is mounted upon by means of ramps. A single pas de souris leads from the main ditch to that part of the ditch of the redoubt in the ravelin which is opposite each flank, and small ramps communicate from thence The communiwith the ditch along the faces. cation with the ravelin, from the ditch of its redoubt, consists of a single pas de souris constructed near the extremity of each face of the ravelin, opposite the postern of the redoubt, besides a double pas de souris at the circular part of the counterscarp of this work; whilst the communication from the main ditch with the redoubts of the re-entering places of arms takes place by means of a pas de souris, either single or double, which is made at the re-entering angle of the gorge. From the ditch of these redoubts,

two single pas de souris, one at each end of the
counterscarp, lead to the terreplein of the re-en-
tering places of arms, and double pas de souris
are made in the circular parts of the counterscarp
at the gorge of the saliant places of arms, in or-
der to ascend upon their terreplein.

When the ditch of the ravelin is not so deep
as the principal ditch, a communication from one
to the other is established by means of a single
pas de souris.

In respect to the caponiers and half-caponiers :
pas de souris
besides the caponier Q, which secures the com-
munication from the tenaille to the
at the gorge of the redoubt of the ravelin, a half-
caponier R covers, on each side of the tenaille,
the passage from the opening between its profile
and the flank of the bastion, to the pas de souris
leading to the ditch of this redoubt, opposite its
flank. A half-caponier S also traverses the main
ditch, perpendicularly to the face of the bastion,
for the purpose of covering, on the side towards
the saliant place of arms in front of the bastion,
the communication with the pas de souris at the
gorge of the redoubt in the re-entering place of
arms; this communication is covered on the
other side, by a half-caponier T, placed across the
ditch of the ravelin. A half-caponier U is like-
wise constructed across the ditch of the redoubt
of the ravelin, which, as has been previously
said, serves to secure the postern, and the pas de
souris situated in that part of the ditch which is
opposite the flank.

In consequence of the manner in which the
gorge of the ravelin and its redoubt is deter-
mined, the besieger can see in reverse, from the
crest of the glacis in front of the bastions, not only
the caponier Q, but also the half-caponiers Ř
nearest to it; and as, according to the present
method of constructing all these works, they
merely consist of earth, the communications
It has therefore been sug-
which they are intended to cover do not appear
sufficiently secure.
gested that the caponier should form a perma-
nent work consisting of a vaulted bomb proof
gallery, A, seven feet six inches high internally,
and ten feet wide; this gallery should be sunk
at bottom about four feet six inches below the
ditch, its sides, as well as the crown of the arch,
being protected by a covering of earth. In this
manner the caponier, besides forming a commu-
nication of itself, will secure from the besieger's
reverse fire two common caponiers constructed
near it, and which, being open at top, may be
covered by means of blinds, when circumstances
require it.

It has been said that Cormontaingne contrived
a retrenchment V for the bastions, which also
answers the purpose of a cavalier; in order to
construct it, draw i'k' and 'l' parallel to the
faces of the bastion, at the distance of eighteen
toises from them; and, at the same distance from
the flanks, draw k'p' and 'o', also parallel to
them, which should be produced inwardly fifteen
feet beyond their intersections m' and n' with the
prolongations Fq' and Wq' of the lines of de-
fence of the collateral bastions; then join p' and
The ditch is six toises broad, and
o', and p'o' will represent the gorge of the re-
trenchment.
the counterscarp parallel to 'K' and i'l.

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