Millions of Muslims visit the Saudi Arabian city of Mecca every year during the Hajj pilgrimage.
One of the main rites of the Hajj is the throwing of pebbles at the Jamarat pillars, which symbolises the stoning of the devil.
It was while travelling to perform this ritual that hundreds of pilgrims were killed and injured on Thursday during a stampede in Mina, just outside of Mecca.
The King of Saudi Arabia has ordered a safety review.
But the health minister says the stampede may have been caused by pilgrims who didn't follow instructions.
Some witnesses deny that, and blame the authorities for not properly managing the large number of people heading towards Jamarat and those coming back.
The government of Iran has expressed its outrage at the deaths of its citizens, questioning Saudi Arabia's ability to handle such large crowds.
Can the kingdom, which prides itself on being the keeper of Islam's two holiest sites, keep the world's largest annual gathering safe?
Presenter - Mike Hana
Khaled Al Maeena - Editor-at-Large, Saudi Gazette
Irfan Al-Alawi - Executive Director, Islamic Heritage Research Foundation
Source: Al Jazeera