Located at the crossroads of several trade routes from the 2nd millennium B.C., Aleppo was ruled successively by the Hittites, Assyrians, Arabs, Mongols, Mamelukes and Ottomans. The 13th-century citadel, 12th-century Great Mosque and various 17th-century madrasas, palaces, caravanserais and hammams all form part of the city`s cohesive, unique urban fabric, now threatened by overpopulation.