The Umayyad Mosque (), also known as the Great Mosque of Damascus (), located in the old city of Damascus, the capital of Syria, is one of the largest and oldest mosques in the world. Its religious importance stems from the eschatological reports concerning the mosque, and historic events associated with it. Christian and Muslim tradition alike consider it the burial place of John the Baptist's head, a tradition originating in the 6th century. Muslim tradition holds that the mosque will be the place Jesus will return before the End of Days. Two shrines inside the premises commemorate the Islamic prophet Muhammad's grandson Husayn ibn Ali, whose martyrdom is frequently compared to that of John the Baptist and Jesus. The site has been used as a house of worship since the Iron Age, when the Arameans built on it a temple dedicated to their god of rain, Hadad. Under Roman rule, beginning in 64 CE, it was converted into the center of the imperial cult of Jupiter, the Roman god of rain, becoming one of the largest temples in Syria. When the empire in Syria transitioned to Christian Byzantine rule, Emperor Theodosius I () transformed it into a cathedral and the seat of the second-highest ranking bishop in the Patriarchate of Antioch. After the Muslim conquest of Damascus in 634, part of the cathedral was designated as a small prayer house (musalla) for the Muslim conquerors. As the Muslim community grew, the Umayyad caliph al-Walid I () confiscated the rest of the cathedral for Muslim use, returning to the Christians other properties in the city as compensation. The structure was largely demolished and a grand congregational mosque complex was built in its place. The new structure was built over nine years by thousands of laborers and artisans from across the Islamic and Byzantine empires at considerable expense and was funded by the war booty of Umayyad conquests and taxes on the Arab troops of Damascus. Unlike the simpler mosques of the time, the Umayyad Mosque had a large basilical plan with three parallel aisles and a perpendicular central nave leading from the mosque's entrance to the world's second concave mihrab (prayer niche). The mosque was noted for its rich compositions of marble paneling and its extensive gold mosaics of vegetal motifs, covering some , likely the largest in the world. Under Abbasid rule (750–860), new structures were added, including the