Nearly 3 million Muslims performing the annual Haj pilgrimage in Saudi Arabia climbed the rocky desert Mount Arafat on Monday, chanting that they have come to answer God's call. The climb is one of the corner stones of the pilgrimage, which is required from every able-bodied Muslim at least once in his life. It is the site where Islam's Prophet Muhammad delivered his farewell sermon, and Muslims believe on this day the doors of heaven open to answer prayers and grant forgiveness.