Damascus was captured by Muslim Arab forces led by Khalid ibn al-Walid in 634. In 661, the Islamic Caliphate came under the rule of the Umayyad dynasty, which chose Damascus to be the administrative capital of the Muslim world. The sixth Umayyad caliph, al-Walid I (r. 705–715), commissioned the construction of a mosque on the site of the Byzantine cathedral in 706. Prior to this, the cathedral was still in use by the local Christians, but a prayer room ("musalla") for Muslims had been constructed on the southeastern part of the building. Al-Walid, who personally supervised the project, had most of the cathedral, including the "musalla", demolished. The construction of the mosque completely altered the layout of the building. While the church (and the temples before it) had the main building located at the centre of the rectangular enclosure, the mosque's prayer hall is placed against its south wall. The architect recycled the columns and arcades of the church, dismantling and repositioning them in the new structure. Professor Alain George has re-examined the architecture and design of this first mosque on the site via three previously untranslated poems and the descriptions of medieval scholars. The new house of worship was meant to serve as a large congregational mosque for the citizens of Damascus and as a tribute to the city. In response to Christian protest at the move, al-Walid ordered all the other confiscated churches in the city to be returned to the Christians as compensation. The mosque was completed in 715, shortly after al-Walid's death, by his successor, Sulayman ibn Abd al-Malik (r. 715–717).