[n] projecting part of a rampart or other fortification [n] a stronghold into which people could go for shelter during a battle [n] a group that defends a principle; "a bastion against corruption"; "the last bastion of communism"
citadel
abatis, acropolis, advanced work, balistraria, bank, banquette, barbed-wire entanglement, barbican, barricade, barrier, bartizan, battlement, beachhead, blockhouse, breastwork, bridgehead, bulwark, bunker, casemate, castle, cheval-de-frise, circumvallatio