Redoubt

Redoubt - Small self-contained fieldwork, a refuge for soldiers outside the main defenses.
Reeded - Parallel convex mouldings.
Re-entrant - Recessed; opposite of salient.

Redoubt
outwork or detached fieldwork defending a pass, hilltop etc. also a temporary defence work built inside a fortification as a last defensive position
Re-entrant ...

Redoubt, Redout, Reduit: (1) A small work placed beyond the glacis, but within musket shot of the covert way, made in various forms, known as a detached redoubt. (2) A small work built in a bastion or ravelin of a permanent fortification.

Castle at Raviscanina: redoubt of the rebel Andrew of Rupecanina.
The Palazzo dei Normanni in Palermo.
A Norman house in Mdina.

redoubt a small defensive earthwork fortification, sometimes temporary, and sometimes used to reinforce a permanent rampart.

See also: Vault, House, Gallery, Arches, Trave