Millions of pilgrims have gathered in Iraq's holy city of Karbala to mark Arbaeen, a sacred Shia Muslim ritual. Arbaeen, also known as Chehlum, commemorates the end of the 40-day mourning period after the killing of Imam Hussein, the Prophet Muhammad's grandson, in a battle in 680 AD. His martyrdom is considered a defining event in the schism between Sunni and Shia Muslims.
Iraqi state-run media said more than 22 million pilgrims have visited Karbala, setting a record for the annual pilgrimage, though that figure could not be independently verified. Last year's Arbaeen drew 17 million pilgrims according to official sources. Arbaeen is the world's largest annual gathering, with the number of pilgrims far exceeding the two million visitors who descend on Mecca for the Hajj. The Kumbh Mela, a mass Hindu pilgrimage, attracts more pilgrims but is held only every three years.