 Complete the following phrase:  In the 630s, the Rashidun Caliphate conquered the region from the Byzantines, beginning the Islamic era in the Levant. Philadelphia was renamed Amman by the Muslims and became part of the district of Jund al-Urdunn. A large part of the population already spoke Arabic, which facilitated integration into the caliphate, as well as several conversions to Islam. Under the Umayyad caliphs who began their rule in 661 AD, numerous desert castles were established as a means to govern the desert area of modern-day Jordan, several of which are still well-preserved. Amman had already been functioning as an administrative centre. The Umayyads built a large palace on the Amman Citadel hill, known today as the Umayyad Palace. Amman was later destroyed by several earthquakes and natural disasters, including a particularly severe earthquake in 747. The Umayyads were 