acropolis
bastion
beachhead
blockhouse
bridgehead
bunker
castle
citadel
donjon
fasthold
fastness
fort
fortificatio
fortification
fortify
garrison
garrison house
guard
hold
keep
martello
martello tower
mote
motte
peel
peel tower
pillbox
post
rath
redoubt
safehold
strong point
stronghold
tower
tower of strength
ward
defence
defense
defensive structure
Alhambra
Bastille
Machu Picchu
Martello tower
Tower of London
alcazar
presidio
sconce
fortressed
fortresses
building
camp
cathedral
cave
edifice
fleet
mansion
monastery
monument
outpost
rampart
territory
town