The dome roof of the Great Mosque at the Citadel of Aleppo, with "bottle" skylights, in Syria.

• The Citadel of Aleppo is a large medieval fortified palace in the center of the old city of Aleppo, northern Syria. 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 BCE. Subsequently occupied by many civilizations including the Greeks, Byzantines, Ayyubids and Mamluks, the majority of the construction as it stands today is thought to originate from the Ayyubid period. An extensive conservation work has taken place in the 2000s by the Aga Khan Trust for Culture in collaboration with Aleppo Archeological Society. Dominating the city, the Citadel is part of the Ancient City of Aleppo, a UNESCO World Heritage Site since 1986.