Around two million Muslims moved into the holy Saudi city of Mina on Wednesday for the symbolic stoning of the devil, one of the high points, but also one of the most risky, of the annual hajj.
Amid tight security, with helicopters hovering overhead and a fleet of ambulances standing by, the human tide converged on the area for the stoning of pillars which will continue on Thursday and Friday.
The crush as pilgrims seek to ensure their stones hit Satan has led to hundreds of deaths in the past, including 345 during the ritual in January last year. A similar tragedy in 2004 saw 251 people trampled to death.
The Saudi Gazette newspaper said 10,000 troops had been deployed in Mina to beef up security and control pedestrian traffic on Jamarat Bridge, from where many throw their stones.
Saudi authorities have built a third level on to the bridge complex to ease the pressure, allowing more than 200,000 faithful an hour to cast pebbles they collected the previous day.
In another change after the deaths of the last hajj, the three "Jamarat" pillars have been extended, each of them effectively being turned into a large wall. This has made them an easier target and lessened the need for pilgrims many elderly and feeble to push to get closer.
"By casting my pebbles I am saying that I will not give in to Satan's worldly temptations," said one middle-aged Arab, who identified himself as Jassem.
According to tradition, Mina is the place where Satan appeared first to Abraham, to his son Ishmael, and to Ishmael's mother Hagar.
After the stoning, the pilgrims will celebrate Eid al-Adha, literally the day of sacrifice, when animals, normally sheep, are sacrificed, in remembrance of Abraham's readiness to sacrifice his son to God.
The hajj reached its climax on Tuesday when the faithful men clad in a two-piece seamless white cloth, the women covered except for the hands and face spent the day praying for forgiveness.
A total of more than 1.7 million pilgrims from 181 different countries have travelled to Saudi Arabia for the hajj, Interior Minister Prince Nayef bin Abdel Aziz said.
The figure was a three percent increase on last year, he said, adding that several hundred thousand residents of the kingdom, both Saudi and expatriate, were also taking part.
Among this year's pilgrims was Iranian President Mahmoud Ahmadinejad, invited by Saudi King Abdullah to become the first president of the Islamic republic to take part.
His pilgrimage has an added political significance because of the sometimes rocky relations between Shiite Iran and Sunni-dominated Saudi Arabia.
An Iranian demonstration during the hajj in 1987 led to Tehran and Riyadh breaking diplomatic relations. Security forces tried to break up the protest and 402 people, including 275 Iranians, were killed.