Hassan Ammar / AP

Tens of thousands of Muslim pilgrims move around the Kaaba, seen at center right, inside the Grand Mosque, during the annual Hajj in Mecca, Saudi Arabia, Oct. 31, 2011. The annual Islamic pilgrimage draws 2.5 million visitors each year, making it the largest yearly gathering of people in the world. The Hajj will officially begin on Nov. 5.

The Hajj is the pilgrimage to Mecca, Saudi Arabia that all able-bodied Muslims, who can afford it, must do at least once in their lifetime. It is a demonstration of the solidarity of the Muslim people, and is the largest pilgrimage in the world.

The Hajj is an ancient ritual, but the Saudi government has had to use modern crowd-control techniques to prevent such things as trampling and architectural collapses that have caused hundreds of deaths during past pilgrimages.

Ammar Awad / Reuters

Pilgrims circle the Kaaba at the Al-Masjid al-Haram in Mecca.

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