Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/473

 FORTIFICATION 449 appears to be 100 per cent. 1 Brialmont no mean authority states it at from 25 to 60 percent., or even 100 percent, if the artillery of the outworks is left out of calculation. In a comparison of the fortress of Posen, which is a faulty application of the polygonal system, with an equally strong fortress on the bastioned system, it has been calculated that the siege park of a besieging army would require 20 per cent, more guns for the attack of the former ; and the writer goes on to state that more siege materials, a greater development of batteries, a greater number of troops, and a larger park are necessary for the attack of the polygonal as compared with the bastioned system. Unquestionably, long exterior sides are advantageous for fortresses ; and admirably, as lias been shown, as the poly gonal trace is adapted for fortresses, it is equally well adapted for detached forts, which are often so small that the bastioned trace is inapplicable to them. The most complete application of this System to a great fortress may be seen in the enceinte of the new fortress at Antwerp, one front of which is shown in Plate V. In this enceinte the main ditch is wet and wide, and flanked by a powerful central self-flanking caponniere ; the flanks are retired and protected by orillons, and the curtain between the latter is broken into two half curtains, separated by a defensible barrack, which forms a retrenched cavalier. The central caponuiere is separated from this curtain by a ditch ; it is, moreover, covered by a counterguard of two branches, revetted with a loopholed counterscarp gallery from which the countermines diverge ; this is further covered by a ravelin of two branches, terminating at the salient in a powerful reverse casemated battery ; the ditches of the ravelin are flanked by low casemated batteries. The ex terior side is 1100 yards Jong, the perpendiculars from the centre of this side marking the saliency of the caponuiere and the retirement of the centre of the curtain are 104 yards and 71 yards long respectively. The curtain is 250 yards long ; the flanks, which are not straight, are formed of two sides, 34 yards and 12 yards long. The flanks of the caponnieres are 27 yards long. The salients of the counterguard and ravelin are 190 yards and 295 yards in advance of the exterior side, and the branches of the latter are directed upon points on the exterior line 245 yards on each side of its centre. The front of the defensible bar rack is covered by the central caponniere, and the flanks are 84 yards long, forming angles of 100 with the front. The main ditch is 88 yards wide at the salients, and 55 yards wide in front of the orillons ; the ditch of the ravelin is GG yards wide at the salient, and 55 yards wide at the low casemated batteries of its flanks. The ditches are unrevetted, with slopes of two-thirds, except at the head of the central caponniere and in front of the curtain and flanks; the depth of water in them is 10 feet, and its surface is 6 feet below the plane of site ; the berms of the enceinte and of the ravelin are 16 feet and 6 feet wide respectively. The command over the country is, in the body of the place, 32 feet at the salients, falling 1 -*- feet to flanks and curtains, in the ravelin 15 feet, in the counterguard 21 feet designed that the outworks may not obstruct the fire of the body of the place ; in the caval iers of the salients the command rises to 41 feet. The parapets are slight, not more than 27 feet thick, but they have very wide terrepleines, and are provided with hollow traverses and large bounettes. The ramps leading to the terrepleines are unusually wide. The guns are either on carriages firing over a 5-feet parapet, or on siege 1 The German engineer Rimpler, writing in 1673, says that, not being agreed with respect to principles, engineers have disputed about insignificant details, while they have neglected two most important conditions, protection for the garrison from the besiegers fire, and the concentration of a more powerful fire upon the besiegers. carriages firing from raised gun banks. The armament is heavy, especially in the central caponnieres and flanks; in the former, 22 guns on each face, viz., 16 in casemates and G in open battery above, in the latter, 14 guns in two tiers. The ravelin has in addition to the guns on its faces 8 case- mated guns in its reverse battery of the salient, and 12 casemated guns in its two low batteries ; and provision is made for armouring the embrasures of these. The covered way is 22 yards wide in front of the body of the place, and from 9 yards to 15 yards wide in front of the ravelin. The communications with the country are wide and ample, two through each front ; they are also level, very direct, and convenient for sorties. Epitomized as this description has necessarily been, it will be seen that advantage has been taken very skilfully of a low site and wet ditch, which while offering serious obstacles to the enemy impede as little as possible the offensive operations of the defenders. For the effective de fence of the fortress, however, a strong and well-handled garrison, prompt to assume offensive measures, and a large armament are necessary. The city of Antwerp, Plate VI., lies upon the east Plate VI bank of the Scheldt, and was originally closely girt by works of the bastioned trace, of which the last remnant, viz., the old citadel, which joined the new enceinte to the river on the south west, has recently been removed. This enceinte consists of 11 fronts of polygonal trace in two lines, of which the G on the south and east line are about 2300 yards, and the 5 on the north line are about 1800 yards from the town, and are closed upon the river to the north by the new citadel, a work of con siderable size and of the polygonal trace also. The fronts are about 1100 yards long, but the two lines join in rather an acute angle ; and to compensate for the weakness of the enceinte at this angle, an advanced ravelin has been con structed on either side which prevents the lines from being enfiladed. The length of the enceinte is about 7 miles ; but as this line of defence would not keep an enemy beyond bombarding range from the town, a line of 8 detached forts has been constructed about 4000 yards in advance of the enceinte. 2 These forts, also of the polygonal trace, are placed about 2200 yards apart; they close on the river on their right, and, extending over a circle of about 10 miles, rest upon an inundation on their left. Both fronts and forts are very strong, and form a great intrenched camp of about 17,000 square acres in extent. The forts are of the same trace, have wet ditches about 50 yards broad, unre vetted scarps, and bomb-proof accommodation for 1400 men in each ; so that to fully garrison the enceinte and the forts about 25,000 men are required. On the west side the river runs in a deep re-entering angle towards the city, and four forts about 2200 yards apart close the space be tween its bends, and form a very strong defence, placing the city upon this side out of reach of the assailant s fire. In England the polygonal trace has of late years been Plate VII. habitually adopted as the most suitable for general pur poses, but it has not hitherto been found necessary to have recourse to a regular and continuous system of forti fication, the insular position of the country, and its pre dominating strength at sea, calling merely for the forti fication of the principal dockyards and military ports, and for the defence of the more important and more exposed harbours. The defence of the military ports is partly on the water and partly on the land, and has been so arranged in the more important ports that they form large naval and military intrenched camps. See Plate VII. As with modern artillery bombardment is practicable at distances of from four to five mil^s, the works of defence commenced considerably in front of this line. IX. -57
 * A second and still more advanced line of detached forts has been