The Great Mosque of Damascus constructed by the Umayyad caliph al-Walid I (reigned 705-715), is a seminal monument of Islamic architecture. The site chosen was the holiest in the city, having successively held temples to the Syrian storm-god Hadad and Jupiter Damascenus and the church of John the Baptist (the mosque still contains a shrine to John the Baptist). The prayer hall used the existing propylaeum and is laid out internally on an east-west axis like a Christian basilica.