(n.) A strong or fortified place; usually, a small fortified place, occupied only by troops, surrounded with a ditch, rampart, and parapet, or with palisades, stockades, or other means of defense; a fortification.

acropolis bastion beachhead blockhouse bridgehead bunker castle citadel donjon fasthold fastness fortress garrison garrison house hold keep martello martello tower mote motte peel peel tower pillbox post rath redoubt safehold strong point stronghold tower tower of strength ward