Muslim pilgrims walk to the holy city of Karbala ahead of the Shiite ritual of Arbaeen, in Najaf, Iraq, on Nov. 30, 2015. Arbaeen marks the end of a 40-day mourning period for the killing of the Prophet Muhammad's grandson Hussein 13 centuries ago. Photo courtesy of Reuters/Alaa Al-Marjani *Editors: This photo may only be republished with RNS-ARBAEEN-PILGRIMAGE, originally transmitted on Dec. 3, 2015.

PHOTOS: The Shiite pilgrimage Arbaeen

(RNS) It's described as one of the world's largest pilgrimages. Drawing an estimated 17 million Muslims to the Iraqi city of Karbala, the Shiite ritual known as Arbaeen dwarfs even the hajj in Mecca. Arbaeen marks the end of the 40-day mourning period after the anniversary of the seventh-century slaying of the Prophet Muhammad's grandson, Imam Hussein, which engendered the Sunni-Shiite schism.  All photos courtesy of Reuters

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