The Citadel is a fortified enclosure begun by Salah al-Din in 1176 AD on an outcrop of the Muqattam Hills as part of a large defensive system to protect both Cairo to the north and Fustat to the southwest. It was the centre of Egyptian government and residence of its rulers until 1874, when Khedive Isma'il moved to 'Abdin Palace. It is still occupied by the military today, but is now open as a tourist attraction comprising, notably, the National Military Museum, the 14th century Mosque of al-Nasir Muhammad, and the 19th century Mosque of Muhammad Ali which commands a dominant position on Cairo's skyline.