September 21-26, 2015 - The Hajj pilgrimage takes place (dates may vary slightly for different countries depending on the sighting of the moon).
Hajj, Hadj or Hadjdj - the spelling HAJJ is the preferred CNN style.
Performing Hajj is one of the five pillars of Islam.
Islam requires every Muslim who is physically and financially able to make the journey to the holy city of Mecca at least once in his/her life.
Hajj occurs two months and ten days after Ramadan ends, during the Islamic month of Dhul-Hijjah.
The height of Hajj corresponds with the major Islamic holy day Eid al-Adha, which commemorates Abraham's readiness to sacrifice his son on Divine orders.
The pilgrimage, conducted over five days, includes numerous detailed rituals including wearing a special garment that symbolizes human equality and unity before God, a circular, counter-clockwise procession around the Kaaba, and the symbolic stoning of evil.
Kaaba (Ka'bah), a cube-shaped structure draped in black silk, is the most sacred shrine of Islam and the chief goal of the pilgrimage.
There is a black stone enclosed in a silver ring in the eastern corner of the Kaaba. Muslims believe that the stone was given to Abraham by the angel Gabriel. Participants touch or kiss the stone to end the ceremony around the Kaaba.
A person who has completed the pilgrimage can add the phrase al-Hajj or hajji (pilgrim) to their name.
1987 - More than 400 people, mainly Iranian Shiite pilgrims, are killed in clashes with Saudi security forces during anti-Western protests in Mecca.
1990 - 1,426 pilgrims are trampled to death.
1994 - A stampede near Jamarat Bridge kills 270 pilgrims.
1998 - One hundred eighty people die in a stampede near Mecca at the end of Hajj.
January 5, 2006 - A small hotel in Mecca, Saudi Arabia, collapses killing at least 76 people. The hotel, Luluat Alkheir, is occupied by Asian pilgrims when it collapses.
January 12, 2006 - A stampede kills at least 363 people. The stampede, like others in the past, happens during the stone-throwing ritual in which the pilgrims stone a symbolic devil.
September 11, 2015 - Days before the start of the Hajj, a construction crane crashes through the roof of the Grand Mosque in Mecca, killing 107 people. At least 238 others suffered injuries when a powerful storm toppled the crane, according to the nation's civil defense authorities. The Grand Mosque is the largest in the world and surrounds the Kaaba.
September 24, 2015 - A stampede kills more than 700 people and injures 800 others, during the ritual known as "stoning the devil" in the tent city of Mina.