ENVELOPE

, in Fortification, is a mound of earth, sometimes raised in the ditch of a place, and sometimes beyond it, being either in form of a single parapet, or of a small parapet bordered with a parapet. These Envelopes are made only to cover weak parts with single lines, without advancing towards the field, which cannot be done without works that require a great deal of room, such as horn-works, half-moons, &c. Envelopes are sometimes called Sillons, Contregards, Conserves, Lunettes, &c.