Muslim pilgrims pray at the top of Mount Noor, near where the Hiraa cave is located on the outskirts of Mecca, Saudi Arabia, on October 21, 2012. The annual Islamic pilgrimage draws three million visitors each year, making it the largest yearly gathering of people in the world. (AP Photo/Hassan Ammar)
(1 of 4) For context, a series of historical images of the Hajj. Here, in 1889,Muslim pilgrims gather in the Valley of Mina, just outside Mecca with tents, camels, and livestock. (Library of Congress)
(2 of 4) In 1889, a view of the Kaaba inside the Masjid al-Haram, in Mecca. (Library of Congress)
On September 7, 1954, Muslims visit the Kaaba, during a pilgrimage to Mecca.
An aerial view of Mecca and the the Masjid al-Haram in 1988.
The Masjid al-Haram, as it stands today. Muslim pilgrims circle the Kaaba as they pray inside and outside the Grand mosque in Mecca.
The Grand Mosque (bottom) and four-faced Mecca Clock Tower (left), viewed from the top of Mount Noor where Muslims believe Prophet Mohammad received the first words of the Koran through Gabriel in the Hera Cave, in Mecca.
The Grand Mosque (bottom) and four-faced Mecca ClocThe Grand Mosque (bottom) and four-faced Mecca Clock Tower
Clouds gather over the Saudi holy city of Mecca as seen from the top of Mount Noor, on the outskirts of Mecca.
Muslim pilgrims pray on a rocky hill called the Mount Mercy on the Plain of Arafat near Mecca.
(left), viewed from the top of M
Muslim pilgrims climb Mount Mercy on the Plain of Arafat.
Muslim pilgrims atop Mount Mercy, during the peak of the annual Halj pilgrimage.
ount Noor where Muslims believe
Muslim pilgrims climb Mount Noor where Muslims believe Prophet Mohammad received the first words of the Koran through Gabriel, during the annual Hajj in Mecca.
rophet Mohammad re
Muslim pilgrims pray at the top of Mount Noor.
Pilgrims pray on Mount Mercy, near Mecca, Saudi Arabia.
d the first words of the Koran through
Lightning strikes, seen from the top of Mount Noor during the Hajj.
The Grand Mosque at night, viewed from the top of Mount Noor.
Gabriel in the Hera
Muslim pilgrims circle the Kaaba and pray at the Grand mosque in Mecca.
Pilgrims pray outside the Grand mosque in Mecca. The annual Islamic pilgrimage draws three million visitors each year, making it the largest yearly gathering of people in the world.
Pilgrims circle the Kaaba inside the Grand mosque in Mecca.
Muslim pilgrims pray in unison inside the Grand mosque.
Cave,
Pilgrims in motion near the Kaaba inside the Grand mosque.
Pilgrims at prayer inside the Grand mosque.
A whirl of pilgrims circle the Kaaba and pray in front of Station of Ibrahim "Maqam Ibrahim" at the Grand mosque during the annual Hajj.
The Grand Mosque at night, viewed fro the top of Mount No
Hajj pilgrims circle the Kaaba and pray at the Grand mosque.
Muslim pilgrims touch the the Yamani corner of the Kaaba, as they pass by it inside the Grand mosque.
The four-faced Mecca Clock Tower, with characters that read "There is no god only the God, and Mohammed is his prophet" before the moon, in Mecca.
A boy stands beside his father, as Muslim pilgrims pray in the Grand mosque in Mecca.
Pilgrims pass by, and reach out to touch the Kaaba in the holy city of Mecca.
Muslims circle the Kaaba.
Muslims Pilgrims head towards Mount Mercy at the peak of the annual Hajj.
Muslim faithful pray outside Namira mosque in Arafat, near Mecca.
Muslims perform the noon prayer outside the Namira mosque in the plain of Arafat on the outskirts of Mecca, on October 25, 2012. Vast crowds of Muslim pilgrims, all dressed in white, flocked from early in the morning to Mount Arafat in Saudi Arabia's west to take part in the main rituals of the annual Hajj.
Thousands of pilgrims perform the noon prayer in the plain of Arafat.
The four-faced Mecca Clock Tower, seen from the top of Mount Noor, in Mecca, during the Hajj.
