Baghdad had for centuries been the capital of the Abbasid Caliphate, the third caliphate, whose rulers were descendants of Abbas, an uncle of Muhammad. In 751, the Abbasids overthrew the Umayyads and moved the Caliph's seat from Damascus to Baghdad. At the city's peak, it was populated by approximately one million people and was defended by an army of 60,000 soldiers. By the middle of the 13th century the power of the Abbasids had declined and Turkic and Mamluk warlords often held power over the Caliphs.