Millions of Shiite Muslims, beating their heads and chests in mourning, packed the Iraqi city of Karbala Thursday for the culmination of one of the world's largest religious events.
The faithful have for days been streaming through the golden-domed mausoleum of Imam Hussein, the Prophet Mohammed's grandson who was killed in 680 AD.
Many in the sea of black-clad devotees swarming the shrine walked days to reach Karbala, sometimes from cities as far as Basra, some 500 km (300 miles) away by road.
"I arrived in Karbala after walking for 12 days," said Mohammed Hussein Jassem, a labourer from Iraq's deep south.
"I found a lot of services on the road," he said, referring to the chain of volunteers who set up "mawakeb", or spots where tents are erected to serve the pilgrims food and beverages.
Baghdad and much of the country south of the capital come to a standstill in the days preceding Arbaeen, as one side of major motorways is reserved for walking pilgrims and the other for authorised vehicles only.
Arbaeen, which means "forty" in Arabic, is an observance that peaks on the 40th day after the anniversary of Hussein's death, but the pilgrimage takes place over several days running up to it.
Karbala Governor Akeel al-Turaihi said on Wednesday that by the end of the pilgrimage on Thursday, an estimated 20 million devotees will have gone through Karbala, setting a new record.
Among them were around five million foreigners, including four million Iranians.
According to the authorities, at least 17 million took part last year, in what was then seen as a show of force in the face of the threat posed by the Islamic State jihadist group, which overran large areas last year.
Protecting the roads to Karbala and Shiite Islam's holiest sites were important priorities for Iraqi security forces and militiamen after the IS offensive.
Provincial leaders said around 30,000 members of the security forces were deployed in and around Karbala.
At least six people were killed in two separate attacks targeting marching pilgrims on Monday in Baghdad, according to police and hospital sources.
Karbala, a city of around 700,000 people, lies between the Euphrates river and the desert expanses of Anbar, a Sunni province where security forces face some of their toughest battles against IS.