As a Haj tour operator, Naseer Ahmed Ansari has been to Mecca 21 times, but never before had he seen such chaos as there was during Thursday’s stampede.

Millions of people head to Mecca every year for the Haj pilgrimage, where strict schedules and routes are maintained to ensure that too many people don’t crowd together at a time. It was a break in this careful scheduling that led to yesterday’s stampede that killed at least 717 pilgrims.