Bastion

n. fortress, stronghold, castle

A bastion is a structure projecting outward from the main enclosure of a fortification, situated in both corners of a straight wall (termed curtain), with the shape of a sharp point, facilitating active defense against assaulting troops. It allows the defenders of the fort to cover adjacent bastions and curtains with defensive fire.
See more at Wikipedia.org...

Noun
1. a group that defends a principle; "a bastion against corruption"; "the last bastion of communism"
(hypernym) defense, defence, defense force, defence force
2. a stronghold into which people could go for shelter during a battle
(synonym) citadel
(hypernym) stronghold, fastness
(hyponym) acropolis
3. projecting part of a rampart or other fortification
(hypernym) fortification, munition

n. bastion, fortress, stronghold, castle

n. bastion, stronghold