Under the first four caliphs - Abu Bakr, Umar, Uthman, and Ali - the Islamic caliphate expanded rapidly through conquest, taking over the Persian Empire and much of the Byzantine Empire. The Umayyad dynasty then ruled from 661-750 AD, establishing their capital in Damascus and expanding the caliphate further west into North Africa and the Iberian Peninsula, and east into Central Asia. The Abbasid dynasty then rose to power in 750, building their new capital of Baghdad and ruling during a period of cultural and scientific achievements known as the Islamic Golden Age, though the caliphate became decentralized over time.