Omayyad Mosque

The Umayyad Mosque, also known as the Great Mosque of Damascus, located in the old city of Damascus, is one of the largest and oldest mosques in the world. It is the fourth holiest site in Islam. 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.

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.

Source: Wikipedia