THESAURUS
acropolis
bastion, beachhead, blockhouse, bridgehead, bunker, castle, citadel, donjon, fasthold, 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
ROGET THESAURUS
acropolis
Refuge
N
refuge, sanctuary, retreat, fastness,
acropolis, keep, last resort, ward, prison, asylum, ark, home, refuge for the destitute, almshouse, hiding place, sanctum sanctorum, roadstead, anchorage, breakwater, mole, port, haven, harbor, harbor of refuge, seaport, pier, jetty, embankment, quay, covert, cover, shelter, screen, lee wall, wing, shield, umbrella, barrier, dashboard, dasher, wall, fort, anchor, kedge, grapnel, grappling iron, sheet anchor, killick, mainstay, support, cheek, ballast, jury mast, vent-peg, safety valve, blow-off valve, safety lamp, lightning rod, lightning conductor, safety belt, airbag, seat belt, antilock brakes, antiskid tires, snow tires, means of escape, lifeboat, lifejacket, life buoy, swimming belt, cork jacket, parachute, plank, steppingstone, emergency landing, safeguard, any port in a storm, bibere venenum in auro, valet anchora virtus.