More than two million Muslims from 165 countries gathered to throw stones at a large wall near the holy city of Mecca, Saudi Arabia on Tuesday. The event shows the believers’ rejection of the devil. It is part of the yearly pilgrimage to Islam’s holy sites known as hajj. But the number of pilgrims in the hajj can make the event risky. In 2015, at least 800 people died when two large groups arrived at the road to the stoning site at the same time. The crush was the worst hajj-related disaster in at least 25 years. Officials in Saudi Arabia have taken several steps to make sure the situation does not happen again. They have created a bridge to ease crowding, and they are using security forces and drones to keep order. Medical workers are also at the scene.