TEHRAN (Basirat): The walk from Najaf to Karbala on the occasion of Arbaeen is a sacred move among Muslims. The Arbaeen pilgrimage to Karbala in Iraq is the largest religious gathering in the world, marking the 40th day after the martyrdom of Imam Hossein (AS) in the seventh-century. Imam Hossein (AS) is the third Shiite Imam and grandson of Prophet Mohammad (PBUH). [PHOTOS]