aerial view of elvas fort in portugal with a bastion, redoubt, tenailles and ditches

architectonic fortification architecture counterguard counterscarp edification sightseeing chauguette cityscape ciudadela geometric undefined bartisan bartizan building entrance exterior flanking hornwork military portugal tenaille cannons citadel covered daytime edifice guerite lunette rampart ravelin redoubt bridge castle facade famous glacis sentry shaped ditch elvas shape stone blue city door draw fort moat star box sky