Arbaʽeen, literally meaning ‘forty’ in Arabic, is a Shiite religious observance commemorating the martyrdom of Husayn ibn Ali and 71 of his companions in the Battle of Karbala in 61AC. Husayn ibn Ali was the grandson of the Prophet Muhammed. It occurs forty days after the Day of Ashura, forty days being the length of mourning for a family member or loved on in many Muslim traditions. It is also the largest annual pilgrimage in the world, in which up to 45 million people go to the city of Karbala in Iraq.