
An aerial view shows the Mecca Clock Tower as Muslim pilgrims walk around the Kaaba in the Grand Mosque in Mecca on November 7, 2011.
It is the holiest city in Islam, the birthplace of the Prophet Muhammad and site of the Koran's composition. More than 13 million Muslims visit this Saudi city annually, several million during the hajj, the pilgrimage that is the fifth pillar of Islam.