When he was 60, the prophet Muhammad returned to Mecca with his followers, and conquered the city.
His founding of Islam changed the course of history, and eventually turned Mecca into an important place of pilgrimage for Muslims.
The Pilgrimage to Mecca (Hajj) is the fifth of the 'Five Pillars of Islam' - the five most important acts of a Muslim (Sunni Islam) under Sharia law.
Special visas are issued to foreigners by the Government of Saudi Arabia, for the purpose of pilgrimage; although entrance to the city itself is forbidden to non-Muslims, as the entire city is considered a holy site in Islam.
Every sane and able-bodied Muslim who can afford to do so is obliged to make the pilgrimage to Mecca at least once in their lifetime, during the last month of the Islamic Calendar (Dhu al-Hijjah, or Month of Hajj).
1. Muharram; 2. Safar; 3. Rabi' al-awwal; 4. Rabi' al-thani; 5. Jumada al-awwal; 6. Jumada al-thani; 7. Rajab; 8. Sha'aban; 9. Ramadan; 10. Shawwal; 11. Dhu al-Qi'dah; 12. Dhu al-Hijjah.
Pilgrimage rites occur during a five-day period, between the 8th and 12th days of the twelfth lunar month.
The event is also marked by the Islamic holiday of Eid al-Adha, which falls on the 10th day of the lunar month.
Some 2 million pilgrims visit the Holy sites during the Hajj and some of the Holy places can be very crowded, particularly at the stoning of the Satans at Mina (BBC stoning story from 2003) and the circumambulation of the Kaaba.
Going to Mecca For Hajj:
Many pilgrims fly to Jeddah, and then travel to Mecca by bus. Some 25,000 British Muslims make the annual pilgrimage.
The Hajj 2006
BBC Diary of The Hajj:
As millions of people stream into Saudi Arabia for this year's Hajj, Rabiya Parekh has joined the pilgrims and is writing a diary for the BBC News website.
CNN's Hala Gorani in Mecca:
Wearing a surgical mask, Hala Gorani reports from Mecca as the Hajj gets underway this Sunday, January 8th.