Muslims worshippers perform prayers around the Kaaba, Islam's holiest shrine, at the Grand Mosque in Saudi Arabia's holy city of Mecca, prior to the start of the annual Hajj pilgrimage in the holy city. The hajj, expected to draw more than two million pilgrims to Mecca this year, represents a key rite of passage for Muslims and a massive logistical challenge for Saudi authorities, with colossal crowds cramming into relatively small holy sites.