TEHRAN (FNA)- This is the world's largest annual gathering. It is held in Iraq and is attended by over 20 million Shia Muslims annually. The religious gathering marks the 40th day of mourning after the martyrdom of the Prophet Mohammad's (PBUH) grandson and Shiite Islam's third Imam, Hazrat Hossein Ibn-e Ali (AS). As an act of religious solidarity, Muslim pilgrims make the journey to the holy city of Karbala on foot. [VIDEO]
