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FORTRESS ; a place which nature and art have rendered fit to resist attack for a protracted period, and even against a superior force. Its object is to delay the enemy by compelling them to institute a siege. The works of a fortress are divided into the mainworks, the outworks and particular defences. The mainworks are situated immediately around the place, and consist of accurately contrived reentering and salient angles, connected by straight lines. By this arrangement, all the parts of the fortress are made to afford each other mutual defence, and are enabled to bring a crossfire to bear from various directions upon the ground in front, which is essential to the defence. The plan of these works must be determined by the localities; and they can therefore seldom be strictly regular. The work which immediately encircles the place is the wall or rampart. Occasionally a second, less elevated, low rampart, or Jhusse braie, runs parallel with this, or is appended to it. The projecting parts of the principal wall are called bulwarlcs, or bastions (see Buhvark, Bastion), (hence what are called bastioned fortresses, such as Marchi, Pagan, Freitag, Vauban, Coehorn, Carmontaigne, and others, were accustomed to construct); or, if the salient and reentering angles are connected without the intervention of straight lines, tenattles (hence the denomination of fortifications en tenaille, such as Dillich, Landsberg and Montalembert propose, but which have as yet been only partially erected). Next to the rampart, and following its outline, comes the large, broad, and deep main ditch, which, wherever circumstances will admit, ought to be filled with water. Outside of the ditch, a low breastwork (the space within which is called the covered way) surrounds the fortress, and sinks to the level of the field, with a gentle declivity (the glacis), so constructed that every shot from the rampart can graze its surface. The outworks and the particular defences, such as mines, towers, blockhouses, abbatis, palisades,&c, lie partly in the ditch, partly in the covered way, and partly yet more in advance and separate from the fortress. The Italian, Spanish, French, Dutch, &c. systems of fortification are all different. They differ in respect to the arrangement of the parts, the contrivance of the lines of defence, and the more or less artificial combination of the same works. A fortress is valuable as a breakwater against the stream of a hostile invasion ; as a bar before passes which do not admit of being turned; as a fulcrum or basis for various operations; as a support for military positions; as a resting place for pursued or beaten forces, or a rallying point for such as would recover breath, or gather, reinforce and rest preparatory to fresh enterprises; consequently as an arsenal, magazine, &c. A fortress which lies out of the way of invasion, and, consequently, can be passed by with ease, and which, moreover, is small, and an object of little consideration with an enemy, answers no good end, can delay an invasion but very little, and does more harm than good, be it ever so strong, since, without rendering any essential service, it keeps a detachment of troops, as its garrison, in a state of inactivity, and is very expensive. Considerable benefit has been expected from a chain of fortresses, the constituent parts of which should mutually assist each other, and bring an enemy, attempting to pass them, between two fires. But to make this scheme feasible, the forts must have active commanders, able to conduct sallies with skill, and indefatigable troops; and the enemy must be imprudent enough not to concentrate all his forces in an attempt to burst through the chain at some one point. The experience of the years 1814 and 1815 has shown that these expected advantages did not exist, although several remarkable instances proved that the event might have been in favor of the scheme, under other circumstances. Scientifically considered, the site of the place is of especial importance in the construction of a fortress. It should be such as to afford facilities of obstructing an enemy's approach; such as will admit of suitable and scientific works without too great expense ; such as will command a complete view of every point within gunshot, and, at the same time, be commanded by no point within that compass. Lastly, a fora*ess must be so situated as not to be unhealthy, and to be as little as possible liable to be cut off; that is, its position near the sea or some river should be such as to render it practicable and convenient at any time 10 receive supplies, and maintain a connexion with troops in the field. The strength of a fortress does not consist in its magnitude. On the contrary, extensive, populous places are difficult to maintain, as they require numerous garrisons, and large quantities of ammunition and provisions, and uncommon watchfulness and activity in the commander. The accuracy and ingenuity of contrivance of numerous and scientific works do not necessarily contribute to make a fortress the more tenable. They are even, in many cases, injurious. It is not the numbers of a garrison that gives strength to a fortress. It is much better to have a well proportioned force; otherwise the defenders are in each other's way, consume the stores, and are deprived of their proper efficiency and usefulness in action.