The ritual is a reenactment. According to the account preserved by the Muslim historian al-Azraqi, when Ibrahim (Abraham) left Mina and walked down toward the defile called al-Aqaba, the Devil appeared to him. Gabriel told him to pelt the tempter. Ibrahim threw seven stones. The Devil appeared again at the middle stone-heap, and again at the little one, and each time the angel said the same thing: pelt him. Seven stones at each site. The three jamarat, the three stone-heaps, stand where those temptations are said to have occurred. The first and largest represents the Devil tempting Ibrahim against sacrificing his son Ismail. The second represents the temptation of Hagar, Ibrahim's wife, to stop him. The third represents the attempt to save Ismail himself from the sacrifice. All three are rebuked.

On Eid al-Adha, the tenth day of Dhu al-Hijjah, pilgrims strike the largest of the three jamarat, Al-Jamrah Al-Aqaba, with seven pebbles. They then cut or shave their hair. For the following two days they hit all three walls with seven pebbles each, moving east to west. The minimum total is twenty-one stones, though a missed throw means collecting more. Pilgrims who stay an additional day stone each wall seven times more. The pebbles themselves are traditionally gathered at Muzdalifah the night before the first throw, though Mina is also acceptable. Behind the simple count, an Islamic theologian's interpretation runs deeper: the stones are cast against the nafs al-ammara, the internal despot, the self that wants what it should not.

Until 2004, the three jamarat were tall pillars. They had been pillars for centuries, but century-scale tradition met modern crowd dynamics and did not hold. Pilgrims on one side threw stones that struck pilgrims on the other side. After the 2004 stampede, Saudi authorities replaced the pillars with 26-meter walls, long enough that stones thrown at one face would not fly past. A multi-tier pedestrian bridge, the Jamaraat Bridge, was built around the walls so pilgrims could throw from ground level or from above, distributing the crowd across elevations. The changes were physical, but the ritual was unchanged in form and meaning. Seven pebbles, three times, three walls, as Abraham was said to have done.

Crowd management is now the single hardest problem at Hajj. The Stoning of the Devil is the most dangerous part of the pilgrimage, because sudden crowd movements near the Jamaraat Bridge can crush people against barriers or against one another. In 2006, a stampede here killed at least 346 pilgrims and injured 289 more. The 2015 Mina crush killed over 2,411, according to the AP count that followed months after the Saudi government's own lower figure. Authorities identified the cause as two waves of pilgrims converging on a narrow road, with luggage and off-route movement adding to the confusion. These were not just casualties. They were mothers on a journey many had saved decades to make. Teachers, laborers, grandparents who had sold land or taken loans for the chance to stand at Mina. The rites they died performing are among the most sacred in their faith.

Mina lies just east of Mecca, a valley transformed every year into a tent city that holds roughly three million people for five days. Outside Hajj it is quiet. The infrastructure, the bridge, the walls, the cooled tents, sits waiting. Then Dhu al-Hijjah arrives, and the valley fills. The ritual that starts in the prehistory of Abraham and continues in real time through engineered walkways is one of the clearest examples in the world of a tradition that refuses to be simplified. The pebble in the hand is the same pebble. The crowd around it is the largest gathering our species performs by choice each year. Both are true at once at Mina.