Millions of Muslims have gathered in Mecca, marking the beginning of the five-day Hajj pilgrimage—the world's largest annual religious gathering. It is year 1446 in the Islamic calendar. Pilgrims are expected to retrace the steps of the Prophet Muhammad,

Large numbers of Muslims converge once a year on Saudi Arabia to unite in a series of religious rituals and acts of worship as they perform the Hajj, the pilgrimage that is one of the pillars of Islam.

Tens of thousands of Muslim pilgrims clambered up rocks and nestled between boulders on Thursday as they embarked on a day of worship under a scorching sun at the Hajj in Saudi Arabia.