Jamarat is a Hajj ritual that involves stoning the three pillars that represent the devil (shaytan in Arabic). As part of this Hajj ritual, the pilgrims throw small pebbles at those three structures in the city of Mina. Pilgrims collect these pebbles at Muzadlifa. These pebbles can also be collected in the city of Mina, east of Makkah.
The historical significance of Jamarat ritual hails from Prophet Ibraheem when the devil appeared to him three times. At each of the appearances, Angel Jibraeel (Gabriel) told Prophet Ibraheem (Abraham) to pelt the devil. Thus, the basis of the significance of the ritual.
All three Jamarat pillars represent the shaytan and represent the three times that Prophet Ibraheem was seduced by the devil when he was going to sacrifice Ismail. At each of the three times, the Angel asked him to rid of the temptation by throwing pebbles at the devil.
As numerous pilgrims flock to the Jamarat site to stone the devil, numerous pilgrims have died over the years due to overcrowding. However, recently the Saudi government has built numerous bridges and extended the Jamarat site to prevent such disasters. As a result, the process has become much smoother than the prior years.
The following video shows the ritual of Jamarat. The second video shows Saudi government’s plans to ease the Jamarat process to prevent smooth flow of the pilgrims to and from the Jamarat site and to prevent overcrowding and stampedes (Second video is in Arabic).