Black-and-white elevated view of the Ibn Tulun Mosque (Masjid Ahmad Ibn Tulun) in the Al-Sayyida Zeinab district of Cairo, showing a solitary figure walking across the wide flat roof flanked by the mosque's distinctive crenellated parapet walls and arched arcades. Built between 876 and 879 CE by Ahmad ibn Tulun, the Abbasid governor of Egypt, it is the oldest mosque in Cairo to survive in its original form and one of the largest in the world. The surrounding urban residential skyline of historic Cairo is visible in the misty background.