A caravan town on the route from southern Arabia to Palestine, the most holy city of Islam; it was the birthplace of the Prophet Muhammad, the founder of Islam, and is a religious center to which Muslims attempt a pilgrimage, or hajj, during their lifetime. Located in the Sirat Mountains in western Saudi Arabia, the focal point of the pilgrimage is the sanctuary which contains the Ka'bah which, according to Islamic tradition, Abraham and Ishmael built as the house of God. The Ka'bah was built before the advent of Islam in the 7th century and has been destroyed and rebuilt several times. Now entirely of stone, it was embellished (according to Mas'udi) with mosaic brought from a church at San'a in Yemen. The town was located about midway between Ma'rib in the south and Petra in the north, and it gradually developed by Roman and Byzantine times into an important trade and religious center. The holy book of Islam, the Qur'an, was revealed to the Prophet partly on Mount Arafat, just outside Mecca.