stronghold, citadel

FORTRESS
WordClue
CASTLEkeep, fortress
ALCAZARMoorish fortress in Spain
BASTIONstronghold
CITADELstronghold, castle
BASTILLEformer fortress in Paris, France
STRONGHOLDcitadel, castle
CITADELstronghold, castle
SYSTEMstructure, arrangement