Almost three million Muslim pilgrims massed on Sunday in a valley near the Saudi holy city of Mina to stone pillars representing Satan, the last and most dangerous rite of the annual hajj.
Hundreds of people have been trampled to death in stampedes which have blighted several previous pilgrimages to Islam's holiest sites when the faithful rush to hurl stones at huge pillars symbolising the devil.
To complete the ritual, pilgrims must throw seven pebbles at each of three 25-metre (82-foot) pillars on the first day of the three-day Eid al-Adha feast marking the end of the hajj, and another seven on each of the last two days.
"This ritual gives me moral strength. Right now I feel as though I'm defeating Satan," said Mokhtar Khan, a 29-year-old who arrived at the site with dozens of fellow Bangladeshis who chanted "Allahu Akbar" (God is greatest).
Another devotee about to perform the ritual, 25-year-old Egyptian Mohammed Husseinin, quipped that he would "feel better once I've stoned Satan, my biggest enemy."
Saudi authorities have installed a multi-level walkway through the site in a bid to avoid the trampling that caused the deaths of 364 people in 2006, 251 in 2004 and 1,426 in 1990.
So far, no major incidents have been reported among the pilgrims, which the Saudi statistics office said numbered 2.93 million this year. The figure includes 1.83 million people from abroad.
The stoning site has been "developed... (and) movement is more fluid and the organisation is better," said the Bangladeshi Khan, who is on his eighth pilgrimage in his capacity as a member of the hajj organising committee.
A large security force monitored worshippers for the stoning after the slaughtering of sheep in a ritual for Eid al-Adha, or the Feast of the Sacrifice, to recall Abraham's willingness to sacrifice his son on God's order.
Most pilgrims did not sacrifice an animal themselves, but instead bought vouchers from the Saudi authorities who then forward meat in the form of aid to poor Muslims in other countries.
After the stoning ceremony, the pilgrims go to Mecca's Great Mosque for a "farewell visit" to the Kaaba, a cube-shaped structure into which is set the Black Stone, Islam's most sacred relic.
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The hajj is one of the five pillars of Islam and must be performed at least once in a lifetime by all those who are able to make the journey.
Mukhtar al-Rahman, who is more than 100 years of age, told AFP that "this is the dream of my life which took a century to come true."
"The crowds have tired me and as you can see I can't stand properly because of the huge crowds flooding" into the area, the elderly Bengali said panting as he looked for a small chair to sit on.
Coping with the world's largest annual human gathering poses a security headache for Saudi Arabia -- guardian of the two holiest Muslim shrines in the cities of Mecca and Medina, the birth places of Islam.
To help prevent chaos, the authorities have numbered buses and tents in Mina and Mount Arafat, where the pilgrims spent Saturday, according to the countries from which the pilgrims have come.
Oil-rich Saudi Arabia has invested billions of dollars over the years to avoid the deadly stampedes that have marred the hajj in the past.
The Chinese-built Mashair Railway, also known as the Mecca Metro, is operating for the first time this year at its full capacity of 72,000 people per hour to ease congestion.
The two-track light railway connects the three holy sites of Mina, Muzdalifah and Mount Arafat.
For the first time this year, the hajj is being streamed live on video-sharing website YouTube in cooperation with the Saudi government.
The stream can be seen at youtube.com/hajjlive.
The ministry of religious affairs sends 3.25 million text messages each day to the mobile phones of pilgrims to inform them of correct procedures for the hajj rites so as to "prevent that which is harmful," ministry official Sheikh Talal al-Uqail told the official SPA news agency.