Ravelin, in fortification, is a work placed before the curtain to cover it, and prevent the flanks from being discovered sideways, it consists of 2 faces meeting in an outward angle. Some ravelins are counter-guarded, which renders them as serviceable as either the cunettes, or tenaillons.
Gorge of the ravelin, is the distance between the two sides or faces towards the place.
Gorges, of all other outworks, are the intervals or spaces which lie between their several wings or sides towards the main ditch. See [Gorges].
Redans, in fortification, are a sort of indented works, consisting of lines or facings that form sallying or re-entering angles, flanking one another, and are generally used on the sides of a river running through a garrisoned town. They were used before bastions. Sometimes the parapet of the covert-way is carried on in this manner.
Redoubt, is a kind of work placed beyond the glacis, and is of various forms. Its parapet, not being intended to resist cannon, is only 8 or 9 feet thick, with 2 or 3 banquettes. The length of the sides may be from 10 to 20 fathoms.
Redoubt, is also the name of a small work, made sometimes in a bastion, and sometimes in a ravelin, of the same form.
Redoubt, is likewise a square work without any bastions, placed at some distance from a fortification, to guard a pass or to prevent an enemy from approaching that way.
Detached-redoubt, is a kind of work much like a ravelin, with flanks placed beyond the glacis: it is made to occupy some spot of ground which might be advantageous to the besiegers; likewise to oblige the enemy to open their trenches farther off than they would otherwise do. Their distance from the covert-way should not exceed 120 toises, that it may be defended by musquet shot from thence.
Redouts-en-cremaillere, so called from their similitude to a saw; the inside line of the parapet being broken in such a manner, as to resemble the teeth of a saw; whereby this advantage is gained, that a greater fire can be brought to bear upon the defile, than if only a simple face was opposed to it, and consequently the passage is rendered more difficult.
Retrenchment, in fortification, is any work raised to cover a post, and fortify it against an enemy, such as fascines loaded with earth, gabions, sand-bags, &c.