In 634–640, as part of the Muslim conquest of the Levant, Syria was conquered by the Muslim Arabs in the form of the Rashidun army led by Khalid ibn al-Walid, under the overall leadership of Abu Bakr, resulting in the region becoming part of the Islamic empire. In 635 Damascus surrendered, its inhabitants being promised security for their lives, property, and churches, on payment of a poll tax. It led to Muslim Rashidun control over the entire Levant and brought about major changes to Levantine religious, cultural and social fabric that continue to this day. Until then, Syria was the main center of Eastern Orthodox Christianity. Conversion to Islam had scarcely begun prior to the invasion, apart from Arab tribes already settled in Syria; except for the tribe of Ghassan, these all became Muslim. The loyalty of his new subjects was paramount to the success of Muslim rule in the region, therefore excessive taxation or oppression was avoided. In the mid-7th century, the Umayyad dynasty, then rulers of the empire, placed the capital of the empire in Damascus.