RE VET3I ENT, in permanent fortification, is a wall of brick or stone retaining the mass of earth which constitutes the rampart, generally on the exterior side only, or retaining the earth which forms the opposite aide of the ditch. The exterior faces of these walls are cote sadered as the snap and counterscarp of the ditch.
In and before the time of Vauban the scarp revetments were raised from the bottom of the ditch to the top of the parapet ; but the part was visible above the glade being destroyed by the enemy's artillsay, and the parapet in consequence partly ruined soon after the commencement of the siege, that engineer in most of his works raised his revetments no higher than the level of the crest of the glacial, or about 7 feet above the natural ground; the exterior of the parapet was then left at such an inclination to the horizon (45* in general) that the earth would support itself. The ditch of a fortress being about IS feet deep, the height of the scarp revetment was consequently 25 feet, and this was considered sufficient to afford security against the danger of baying the rampart escaladed. At present it is recommended that the main ditch should be 24 feet deep, and in this case the scarp seeetment is above 30 feet high. In constructing the fortifications of Neuf Brisac. Vauban made the revetments of the saris both of the enceinte and of the rednit of the ravelin, as high as the top of the parapet; but these works being covered by the counterguard or the ravelin, their revetments would be unseen by the enemy at a distance, and therefore not liable to the objection above mentioned.
The torus usually given in profile to revetments of masonry may be seen at 31 and N, Fig. 2, the first is the revetment of the eounterecarp, and the other that of the scarp. The rectangular parts are sections through the counterforta or buttresses which are built up with the walls in order to strengthen them, at intervals of about 15 feet from each other. Scarp revetments, whose tops are as high or higher than the crest of the glacial, are called full revetments ; while such as are no higher than the level of the natural ground are called demi revetments.
In order that the revetment might most effectually resist the presaure of the earth which it is to support, Vauban gave to the exterior face of the wall a slope, whose horizontal breadth was equal to one-fifth of the height ; this was subsequently reduced to one-sixtb, and now it is thought to be most advantageous to make the face vertical. By giving the slope to the rear face of the wall, that is, by making the revetment counteralopine, all the advantages of a slope are gained, while the disadvantage of rapid vegetation on the face is avoided.
In laying the foundations of revetments in defective soils, the same methods are used as in the construction of civil edifices; and in all cases the courses of stones or bricks are laid obliquely to the horizon, inclining down towards the part under the earth which is to be sup ported, in order that the 1 ressure of the latter may be more directly resisted. But as the bed-joints of brickwork when so disposed allow the rain to penetrate, and the seeds of grass to lodge in them, it is thought that the wall is more speedily degraded when so built than when the courses are laid horizontally; therefore in order to unite the advantages of direct resistance and durability, it is customary to place the courses obliquely, but to lay one row of bricks in each course at the face of the wall in a horizontal position.
The exterior and interior faces of the revetment, or retaining wall of a dock, have in a vertical section the (unit of concentric arcs of circles, with their convexities towards the land ; and this form is given them that the atones may be able to resist the hydrostatical pressure of any water which, when the dock is full, rimy get behind the wall, and which may be prevented (ruin escaping when the dock is made dry.