Each year, Muslims from all over the world go on a pilgrimage to the holy city of Mecca in Saudi Arabia, known as hajj. A scholar explains its spiritual significance.
After years out in the cold, the Iranians have a chance to be heard in the West – and they've got Saudi Arabia on their minds.
Computer models can help planners deal with large groups of people but we need better insight into the psychology of crowds to make them accurate.
A deadly crowd crush has killed over 300 people at this year's Hajj. Is the pilgrimage industry just too big?