An estimated 14 million Shi'ite pilgrims thronged Iraq's holy city of Karbala on November 10 to mark the annual Arbaeen commemoration.
Arbaeen is one of the biggest religious festivals on earth and marks the end of the 40-day mourning period for the 7th-century killing of Imam Hussein by the forces of the Caliph Yazid -- a formative event in Shi'ite Islam.
The Arbaeen holiday is observed in Shi'ite communities worldwide, with large gatherings in Iran and southern Lebanon.
Under tight security in Karbala, around 14 million worshippers crowded into the golden-domed mausoleum where the Prophet Muhammad's grandson is buried, religious authorities said. The pilgrims beat their chests in unison against a background of religious music.
Iranian officials said more than 2 million Iranian pilgrims had crossed the border to participate.
Imam Hussein's killing in the Battle of Karbala in 680 AD was part of a fierce dispute over who should succeed the Prophet, which eventually developed into a schism between the Sunni and Shi'ite branches of Islam.
Tens of thousands of security personnel and Shi'ite militiamen were deployed, as in past years, around the perimeters of the shrine as well as on all roads leading to Karbala, about 80 kilometers southwest of Baghdad.
This year's commemoration comes as Iraqi forces have expelled the extremist Sunni group Islamic State from most of its strongholds in the country.
IS has repeatedly targeted attacks on Iraq's Shi'a. Last year, it claimed responsibility for a suicide bombing that killed at least 80 mostly Iranian worshippers as they were returning home from the festival.
Despite heavy security at this year's commemoration, with helicopters flying overhead, attendance appeared to be down from the roughly 17 million to 20 million people estimated at the event last year.
Based on reporting by AP and AFP