Ravelin
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Ravelin
a separate enclosed triangular fortification work, situated in front of the moat, in the interval between the bastions.
The ravelin was designed to cover a section of the fortress wall (curtain), the fortress gates, and other structures from artillery fire and attacks of the enemy. It was also used for cross fire at the approaches to the perimeter of the fortress, for fire support for neighboring bastions, and for an assembly point for troop sallies. Ravelins were used from the 16th to early 20th centuries.
ravelin, demilune
In fortifications, a projecting outwork forming a salient angle.