A detail of an ancient gate at the Citadel in Aleppo, Syria..The Citadel in Aleppo is a large medieval fortified palace in the centre of the old city. It is considered to be one of the oldest and largest castles in the world. Usage of the Citadel hill dates back at least to the middle of the 3rd millennium BC. Subsequently occupied by many civilizations including the Greeks, Byzantines, Ayyubids and Mamluks. It is now a World Heritage site.