From the work of the gorge is a communication into the fort by a covered caponnière, forming traverse in the direction of the _capital_ or centre line. The gorge is defended by a curtain for the riflemen, and, at need, for small pieces of artillery. At need also, on the terre-plein of the work of the gorge may be mounted guns of long range, affording an indirect fire in the circumference of a semi-circle, over the great traverse H, if the parapets of the faces are damaged by the fire of the enemy.
Fausse-braies consisting of palings are fixed in the ditch at ten feet from the base of the escarp, to hinder the fallen _débris_ of the escarp from filling up the ditch, and to enable its passage to be defended. The well-covered internal masonry works prevent the accumulation of earth on the interior platforms, and afford casemates, which enable the garrison to take rest in perfect security; at any rate along the two faces and the great traverse. Blindages can be set up on the traverses of the batteries, and can be easily repaired every night, as well as the escarp of tipped earth.
It would be difficult to say how many projectiles it would require to render such a work untenable; since we have seen in the siege of Paris, that a marine battery erected on tipped earth on the military road between the forts of Rosny and de Noisy, armed with three guns, had been a mark for the German shells during twenty-four days, without any of its guns having been dismounted, or its escarp suffering more than could be made good each night.
Permanent works should, however, only be established with the utmost circumspection:--1. Because they require a very considerable outlay. 2. Because they are necessarily familiar to, and for a long while studied by the enemy, who takes his measures accordingly.
The important point is to possess an accurate acquaintance with the ground to be defended, and only to establish permanent works in second line, and on points incontestably favourable for defence, supposing an artillery of even a still longer range than the present.
Every centre to be defended should therefore possess works sufficient to prevent a surprise; and in addition at a distance of six to eight thousand yards, a line of forts, crossing their fires if possible, or at any rate connected by strong batteries; and lastly, at a distance of about four thousand yards, positions previously examined and known, suitable for placing very simple works of field fortification, but which at a given moment may offer a resistance sufficient to permit movements on a grand scale--and delay the formation of an enemy's batteries.