Despite threats of violence, millions of Shia Muslim pilgrims gathered in the Iraqi city of Karbala on Sunday for the ceremony of Arbaeen.

Arbaeen commemorates the death of a grandson of the Prophet Mohammed. The ceremony is held to mark the death of Imam Hussain, who was martyred in battle at Karbala.READ MORE:World’s Biggest Pilgrimage, And Why You’ve Never Heard of it!Video:World’s Biggest Pilgrimage Known as Arbaeen