Synonyms and related words :
acropolis, bastion, beachhead, blockhouse, bridgehead, bunker, castle, citadel, donjon, fastness, fort, fortress, garrison, garrison house, hold, keep, martello, martello tower, mote, motte, peel, peel tower, pillbox, post, rath, safehold, strong point, stronghold, tower, tower of strength, ward