ravelin

A detached triangular work in fortification, with two embankments which form a projecting angle.

A detached work with two embankments which make a salient angle. It is raised before the curtain on the counterscarp of the place. Formerly called demilune and half-moon.

A fortification outside a castle used to split an attacking force; composed of two faces, forming a salient angle whose gorge resembles a half-moon