The Citadel of Cairo or Citadel of Saladin is a medieval Islamic-era fortification in Cairo, Egypt, built by Salah ad-Din (Saladin) and further developed by subsequent Egyptian rulers. It was the seat of government in Egypt and the residence of its rulers for nearly 700 years from the 13th century until the construction of Abdeen Palace in the 19th century. Its location on a promontory of the Mokattam hills near the center of Cairo commands a strategic position overlooking the city and dominating its skyline. When it was constructed it was among the most impressive and ambitious military fortification projects of its time. It is now a preserved historic site, including mosques and museums.

Cairo is the capital of Egypt and the city-state Cairo Governorate, and is the country's largest city, home to 10 million people. It is also part of the largest urban agglomeration in Africa, the Arab world and the Middle East, the Greater Cairo metropolitan area, which is the 12th-largest in the world by population with a population of over 22.1 million.