The Terreplein of the rampart is usually 40 feet in width. A 24-pounder mounted upon a siege carriage, (which is the longest,) requires for its recoil about 24 feet, and the remaining space is necessary for the passage of ammunition wagons. The terreplein is the part of the rampart on which the besieged places himself and his artillery: the rampart is surmounted by another body of earth of less thickness, (20 feet at most,) called the parapet, which is intended to cover those upon its terreplein.
The height of the crest of the parapet of the body of the place, should be such, that a bullet fired from it may reach the third parallel, established by the besieger at the foot of the glacis, and may pass 4 feet above the crest of the covered way, so that the soldiers defending that work, may fire at the same time without being incommoded by the wind of the bullet.
“Of the various methods of facing the exterior side of the rampart, which is called the Scarp, that in masonry is to be preferred, particularly when it is at least 25 feet in height. At this height is requires ladders of such a weight, to scale it, as cannot easily be managed. An earthen scarp, with a wet ditch, has the fault of exposing the place to be taken by surprise in time of severe frosts. An earthen scarp, upon a dry ditch, is the worst of all, as it may at any time be scaled by cutting its palisades with a hatchet. In besieging it, it does not become necessary to establish batteries in breach, a passage of the ditch alone will be sufficient, as the natural slope of the earth of the rampart will permit it to be mounted.”
“An earthen counterscarp spares the besieger the long and dangerous labour of the descent of the ditch, and facilitates the capture of the whole covered way when once a part of it is taken”. (Bousmard)
Source: Lallemand, Henri Dominique: A Treatise on Artillery (New York 1820)