16) 



FORTIFICATION. 



FORTIFICATION. 



170 





should be within range of the flanks. This for the old smooth-bored 

 musket would have required a range of 180 to 200 yards, but this being 

 impracticable from the relief required io the bastion, and from its 

 further rendering the bastion too small, the length is determined by 

 the range of rifles, wall pieces, and grape shot, which is about 300 yards. 

 Now these being supposed to be placed on the flanks, as at e or/, 

 might be employed to oppose the formation of the counter-battery at 

 H, or at the corresponding point on the left of F ; therefore, if we 

 assume the length of the line from e to H to be 300 yards, and deduct 

 from it the estimated breadth of the main ditch and covered-way (40 

 yards), we have 260 yards for the length of e E or / F, which is called 

 the line of defence. This is also the distance of K or F from the 

 shoulder of the collateral bastion ; and if we add to it the length of 

 the face of the bastion, which is 103 yards, or 2-7ths of E F, in order 

 that, in the inferior polygons, the bastion may have sufficient capacity, 

 we obtain about 380 yards for the distance between the salient points 

 F and E of the two bastions ; and it may be observed, that a few yards 

 more or less in the dimensions need not be regarded. 



The directions of the faces of the bastions on each front coincide 

 with lines drawn from ^he angles E and F of the polygon, through the 

 extremity of a perpendicular let fall from the middle of the line E F 

 and made equal to one-sixth of that line ; and each flank is the 

 chord of an arc, described either from the opposite angle E or F of 

 the polygon, or from the nearest shoulder of the collateral bastion, 

 as a centre. By this construction the flank is rather greater in length 

 than the enemy's counter-battery, which is necessarily limited by the 

 angle of the glacis and the prolonged face of the nearest bastion ; 

 and it is nearly perpendicular to the direction of that face : the reason 

 why it is not made exactly so is, that a man on the flank, placing his 

 musket perpendicular to the line of parapet, will thus be able to fire 

 into and defend a breach which may be made in the face of the 

 collateral bastion. The curtain is determined by a line joining the 

 interior extremities, near e and/of the flanks; and, with the height 

 which Vauban assigned to the rampart of the enceinte, this length 

 will permit the fire of musketry from each flank to defend the opposite 

 half of the ditch between the flanks. The line which on the plan 

 indicates the directions of the faces, flanks, &c., of the works, is called 

 the magistral Una ; it forms the exterior side of the ramparts in fy. 1 

 [BASTION], and coincides with the cordon, or projection, at the top 

 of the revetment N, fig. 2. 



The dimensions of the ditch are determined by the necessity of 

 obtaining from it the earth for the formation of the ramparts and 

 parapets, the depth being fixed by giving the escarp the least height 

 which is considered quite secure from escalade. This for the main 

 works should be about 32 feet, which gives a breadth of ditch at the 

 flanked angles of the bastion of 38 yards. The counterscarp wall is 

 rounded opposite the flanked angles at E or F, and is directed from 

 thence towards the shoulder of the collateral bastion. 



The improvements made by Vauban in the ravelin are described 

 under RAVELIN : o, represents one-half of that work ; and it will be 

 merely necessary here to say, that its plan is determined by using the 

 angular points near 6 and /, formed by the magistral lines of the flanks 

 and curtain, as centres, and with radii equal to the distances from 

 thence to points taken on the faces of the collateral bastions, at 10 yards 

 from their shoulders, describing arcs ; the intersection of these arcs 

 determines the salient angle of the ravelin ; the magistral lines of its 

 faces tend from that intersection to the points just mentioned, and 

 terminate on the counterscarp of the main ditch. 



The traverses in the covered way were proposed by Vauban, in order 

 to diminish the effect of the ricochet tire of the besiegers, which 

 Vauban was the first to employ in the attack, in which he was even 

 more famous than in the defence, being the first to give it that decided 

 superiority which it has ever since maintained, and one of the principal 

 means of which was the ricochet fire. He was the first engineer who 

 formed the spacious places of arms, as they are called, at L, in the re- 

 entering parts of the covered-way, in order to obtain room for assembling 

 troops, and to afford a good crossing fire of musketry from their faces 

 for the defence of the glacis in front of the bastions and ravelins. 



An attention to the reliefs of the several ramparts of a fortress is no 

 less necessary than to the plans ; for, as it would be advantageous, 

 when the approaches of the besiegers are near the foot of the glacis, 

 that a fire of artillery should be made from the ramparts of the 

 enceinte or ravelin, and of musketry from the covered- way at the same 

 time, the reliefs of those ramparts should be determined by imagining 

 a line to be drawn from the foot of the glacis through a point 3 or 4 

 feet vertically above the crest of the latter, that is about 11 feet above 

 the ground, and to be produced through the parapet of the said enceinte 

 or ravelin ; then, if the soles of the embrasures, which are necessarily 

 4J feet below the crest of the parapet, be made to coincide with such 

 imaginary line, the fire of artillery from them may be directed to the 

 enemy's trenches without incommoding the defenders of the covered- 

 way. The crust of the enceinte thus determined will be about 18 feet 

 above the ground, and that of the ravelin about 3 feet less. 



The tenaille, f.Jiy. 1 [BASTION], will be described under that word; 

 but it may be mentioned here that the relief of this work is determined 

 by the consideration that, while it should be high enough to mask the 

 postern hi the curtain behind it, the men stationed on it to defend the 

 ditch should be below the lines of fire from the flank of one bastion, 



when directed to the foot of a breach supposed to be made near the 

 shoulder of that which is collateral to it, in order that they may not 

 be injured by that fire. 



As Vauban had occasionally to adapt works constructed according 

 to the principles above mentioned, to the old fortifications which then 

 existed, the particular method employed in disposing them acquired 

 the denomination of his second system ; and when, subsequently, he 

 fortified Neu Brisach, some few modifications which he was led to 

 make gave rise to a new distinction, the works of that place being con- 

 sidered as forming a third system. In both these systems the bastions 

 v,Jig.3 [BASTION], are separated by a ditch from the enceinte; and 

 this circumstance is so far advantageous, that the place would not be 

 compelled to surrender immediately upon those works being taken by 

 the besiegers. The enceinte consists of a long curtain, either quite 

 straight or broken by two short flanks ; and at the angles of the polygon 

 are small bastion-towers of masonry (T,Jiy. 3), in whose flanks are 

 formed casemates to contain artillery for the defence of its ditch. 

 This great engineer died in 1707, at the age of 74 years; and, from 

 his time, the French fortification has been to a great extent that of all 

 Europe. 



It would be improper in this place to omit the name of Minno, 

 Baron of Coehorn, who was born in the year 1641, the year preceding 

 the birth of Vauban, and who in the service of the United Provinces 

 acquired a reputation scarcely inferior to that of his great rival. In 

 the year 1692 they were directly opposed to one another, Coehorn 

 defending Namur against Vauban, who conducted the attack. His 

 system, or systems, as he in his treatise describes three, are essentially 

 adapted to aquatic sites, such as those of Holland, and he applied them, 

 with the modifications required by the ground, to Niineguen, Breda, 

 Manheim, Namur, and Bergeu-op-Zoom. Tilbury Fort is also on his 

 system. The outline of the plan differs but little from that of his 

 rival's great system, but the shoulders of the bastions are strengthened 

 by large towers, or orillons, containing casemates. - In the interior of 

 each bastion is another, on a higher level, and on the exterior is a 

 counterguard, consisting of two faces, parallel to those of the bastion. 

 A large ravelin, inclosing a redoubt on a higher level, is placed before 

 the curtain, and the whole U surrounded by a broad covered-way, 

 whose places of arms are retrenched by brick redoubts. The plane of 

 site of the works is assumed to be 4 feet above the level of the water, 

 which allows the system to combine the advantages of wet and dry 

 ditches. When the wet ditches are employed the expense of the revet- 

 ment is saved, and the dry ditches which separate the uurevetted 

 portions from the principal works afford the garrison a great advantage 

 in resisting the besieger while defiling from his bridge across the wet 

 ditch to attack the inner works, which have a sufficient revetment to 

 resist an assault without ladders, but are still low enough to be pro- 

 tected from distant fire. The terrepleins, as well of the bastions and 

 ravelins as of the covered-way, are sunk below the natural surface of 

 the ground, so that it would be impossible, in the marshy soil on which 

 the fortifications are supposed to be constructed, for an enemy to dig 

 trenches there in order to form covered approaches. The terrepleins 

 of the principal works are also well defended by fire from the covered 

 galleries which cross them, or which are formed within the masses of 

 the ramparts. 



It should be observed that the salient points, E, F, &c., of the bastions 

 and ravelins in Vauban's system being nearly equally distant from the 

 centre of the place, the trench executed by the besiegers to connect 

 the glacis before the former works will also connect that which is 

 before the latter ; and that, in consequence of this construction, 

 breaches may be formed, and assaults made, at one time, in the enceinte 

 and outworks. With the view, therefore, of preserving the former 

 untouched till some time after the ravelins may ha* been taken, the 

 French engineer Cormontaingne proposed, about 30 years after the 

 death of Vauban, to advance the salient points of the ravelins as much 

 as possible, by increasing the length of the faces to the utmost limit 

 which a regard to the due magnitude of the flanked angle will admit. 

 Thus the magistral line of his ravelin is determined by directing its 

 faces on the faces of the collateral bastions, at 22 yards from the 

 shoulders ; and its salient or flanked angle by the intersection of the 

 perpendicular produced of an arc described from one.of these points 

 as a centre, and the shoulder of the opposite bastion as a radius. By 

 this construction it would become impossible for an enemy to crown 

 the glacis of a bastion till he had got possession of the two collateral 

 ravelins, on account of the fire which, from these, might be made upon 

 his approaches between them ; and the fall of the place would be 

 delayed by the time spent in conducting the approaches from the 

 ravelins to the intermediate bastions. 



In order that this benefit might be obtained in the highest degree, 

 Cormontaingne suggested the propriety of fortifying places on polygons 

 of the superior kind, and even, when possible, of constructing two or 

 more fronts of fortification on one straight line ; this practice would 

 have the additional advantage of rendering the flanked angles of the 

 bastions very obtuse, by which, not only would the increased capacity 

 of those works pernu't stronger retrenchments to be formed in them, 

 but the faces being produced outwards, would tend to points on the 

 faces of the ravelins, and thus would be completely secured from the 

 enfilading fires of the besiegers. 



Besides the above general modifications, Cormontaingne made several 



