In the middle of the thirteenth century, non-Arab manumitted slave soldiers (known as mamluks) took power after the death of the last Arab Ayyubid ruler of the medieval Sultanate of Egypt. The Mamluks gradually grew in strength and expanded east and west, offering Egypt a long period of prosperity and stability. In the winter of 1468, Al-Ashraf Sayf al-Din Qa'it Bay (a slave of the ninth Mamluk sultan) became sultan and ruled for three decades. He was greatly admired as a defender of Islam and a patron of scholars (despite his humble background). He endowed his empire with countless hospitals, libraries, mosques, and caravanserais. Unfortunately, he was also forced to deal with many threats, including the plague that ravaged the population of Egypt, and the Ottoman Turks, who were a growing threat from the north. His desire to protect Alexandria made him build the citadel of Qaitbay.