Envelope

in fortification, a work of earth, sometimes in form of a single parapet, and at others like a small rampart: it is raised sometimes in the ditch, and sometimes beyond it. Envelopes are sometimes en zic-zac, to inclose a weak ground, where that is practicable, with single lines, to save the great charge of horn works, crown works, and tenailles, or where room is wanting for such large works. These sort of works are to be seen at Besancon, Douay, Luxembourg, . Envelopes in a ditch are sometimes called sillons, contregardes, conserves, lunettes, . which words see. To ENVIRON , to surround in a hostile manner, to hem in, to besiege.