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 (noun)
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Use "ravelin" in a sentence
"From the land side, it was only approachable by a causeway across the swamp, and this was guarded by a strong ravelin, which is the military name for an outwork erected beyond the ditch of a fortress."
"I would also have you acquire a general notion of fortification; I mean so far as not to be ignorant of the terms, which you will often hear mentioned in company, such as ravelin, bastion; glacis, contrescarpe, etc."
"And he laid his hand, as Drayton might have said, on that stout bastion, hornwork, ravelin, or demilune, which formed the outworks to the citadel of his purple isle of man."