More than two million Muslim pilgrims began the ritual stoning of the devil today in what is the climax of the annual haj pilgrimage.
The occasion has led to deadly stampedes in the past, and some pilgrims rushed to the site early in the morning to cast their first set of stones before the crowds arrived.
Some 250 pilgrims were crushed to death in 2004 at Mena's Jamarat Bridge, where the millions of pilgrims must stand to stone three thick walls in a symbolic casting out of the devil and rejection of temptation.
King Abdullah and Crown Prince Sultan, in a message marking today's Eid al-Adha holiday, said: "We ask God to make this Eid one of peace and stability for Muslims and the whole world and unite Muslims in goodness and inspire them to do what is right."
Saudi Arabia has deployed a record 60,000 security men to control the huge crowd and avert attacks by Islamist militants fighting the US-allied Saudi royal family.
This year's pilgrimage, a once-in-a-lifetime duty for every able-bodied Muslim, has been overshadowed by the collapse of a Mecca hostel that killed 76 people last Thursday and warnings of a possible spread of deadly bird flu due to the huge crowds.
Pilgrims - male and female - complete the first stoning session and then go to Mecca to circle the Kaaba, which symbolises the house of God, dressed in white robes meant to eradicate class and make all Muslims equal.