ADJ. great | formidable, impregnable, strong | grim
VERB + FORTRESS attack, besiege, lay siege to | take Greek warriors took the fortress with little effort. | hold, occupy
FORTRESS + VERB be/come under attack, be/come under siege | fall The fortress fell after a nine-day siege.
FORTRESS + NOUN town
PREP. in a/the ~ They took refuge in the fortress.