The Hajj pilgrimage draws millions of Muslims from around the world every year to Mecca, the birthplace of the Prophet Muhammad, Islam's holiest place. Saudi Arabia expects to host perhaps three million people in a ritual journey that every able-bodied Muslim who can afford it must make at least once in their lifetime. It is the largest annual gathering of humanity anywhere. Timed to the Muslim lunar calendar, the Hajj is followed by the celebrations of the three-day festival of Eid al-Adha, or the Feast of Sacrifice, which symbolizes Abraham's willingness to sacrifice his son. A Muslim pilgrim prays as visits the Heeraa cave at the top of Noor Mountain on the outskirts of Mecca, Saudi Arabia on November 2, 2011.

According to tradition, Islam's Prophet Mohammed received his first message to preach Islam while he was praying in the cave. Muslim pilgrims climb a rocky hill called the Mountain of Mercy on the Plain of Arafat near Mecca, Saudi Arabia on November 5, 2011. Tens of thousands of Muslim pilgrims move around the Kaaba (center) inside the Grand Mosque in Mecca, Saudi Arabia on November 3, 2011 Tens of thousands of Muslim pilgrims pray inside the Grand Mosque in Mecca, Saudi Arabia on November 4, 2011 The Mecca Clock Tower dominates the city as Muslim pilgrims walking around the Kaaba in the Grand Mosque of the holy city of Mecca during the annual Hajj pilgrimage rituals on November 7, 2011.

Tens of thousands of Muslim pilgrims move around the Kaabaa (center) inside the Grand Mosque in Mecca, Saudi Arabia on November 3, 2011.
Muslim pilgrims pray on a rocky hill called the Mountain of Mercy on the Plain of Arafat near Mecca, Saudi Arabia on November 5, 2011 Muslim pilgrims cast stones at a pillar, symbolizing the stoning of Satan, in a ritual called "Jamarat," the last rite of the annual Hajj, in Mina near the Saudi holy city of Mecca, Saudi Arabia on November 6, 2011 Thousands of Muslim pilgrims arrive to throw pebbles at pillars during the "Jamarat" ritual, the stoning of Satan, in Meenaa near the holy city of Mecca, on November 6, 2011. Tents of Muslim pilgrims recede into the distance at Mina, Saudi Arabia on November 7, 2011.

Thai Muslim pilgrims offer prayers before they depart for the annual Hajj pilgrimage to Mecca at the Hat Yai International airport in southern Thailand on October 5, 2011. Paakistaanee traders wait for customers to sell their livestock for the upcoming Eid-al-Adha festival in a market in Islaamaabaad, Paakistaan on November 4, 2011. A man carries a sacrificial goat on sale at a market, ahead of the Eid al-Adha feast, in Sanaa, Yemen on November 5, 2011. Russian Muslims pray outside St Petersburg's mosque during the first day of the Eid al-Adha on November 6, 2011 Muslim women perform Eid al-Adha prayers in Srinagar, Kashmeer on November 7, 2011 A young Indian Muslim boy smiles with a sacrificial goat on Eid-al-Adha in Allahabad, India on November 7, 2011.