ravelin

Ravelin enters English from the French ravelin, from the Italian rivellino, whose own etymology is uncertain — possibly from the Latin revellere (to tear away, to detach). The uncertainty fits: a ravelin is a detached work, separated from the main fortification by a ditch, positioned in front of the curtain wall between two bastions. It is deliberately placed where it will be attacked first.

The ravelin appeared in Italian fortification design in the fifteenth century as gunpowder transformed siege warfare. The triangular shape — point facing the enemy — deflected cannon fire along its angled faces rather than absorbing it head-on. The ravelin also shielded the curtain wall behind it from direct fire. An attacker had to capture the ravelin before they could assault the main wall. It was a sacrificial defense.

Vauban made the ravelin standard in late seventeenth-century French fortification. His designs placed ravelins in front of every curtain wall, connected to the main fortress by covered passages (caponnières). The ravelin at the Citadelle de Lille, completed in 1670, is one of the finest surviving examples. Some of Vauban's ravelins had their own internal defenses — a ravelin defending a ravelin.

The word has no figurative English use. Unlike bastion, fortress, and stronghold, ravelin never left the military vocabulary. It is too specific, too geometric, too tied to the mathematics of artillery angles. The word stayed in the ditch where it was built.