Hundreds of thousands of Shia Muslims are in the Iraqi town of Karbala to mark the festival of Ashura for the first time in more than 30 years.
The festival was severely restricted by Saddam Hussein.
Ashura is the climax of a 10-day period of mourning for Shias commemorating the martyrdom of Imam Hussain,
who was killed in Karbala in 680 AD.
His death is being marked by rhythmic chanting and ritual self-flagellation from devotees clad in black.
Over 2 million people are expected in Karbala in time for the festival's climax on Tuesday.
Many of the devotees this year have come illegally from neighbouring Iran, which, like Iraq, has a majority Shia population.
Years of suppression
Shias were repressed under Saddam Hussein's Sunni-dominated regime.
Observation of Ashura was hampered by a ban on the practice of ritually beating themselves and - among some Shia groups - of cutting wounds in their skin.
Pilgrims from Iran - a wartime enemy of Saddam Hussein's Iraq - were also not welcome at Karbala, one of Shia Islam's holiest sites.
The death of Hussein, the grandson of the Prophet Mohammad, cemented the split between Sunni and Shia Islam over who should inherit lead the faith.
The BBC's Barbara Plett says the Ashura processions were tightly controlled not only by Saddam Hussein but by the Sunni rulers of Baghdad who preceded him - all saw them as dangerous rallying points for resistance.
Security fears
"We have been waiting for this ceremony for 30 years. I can't begin to describe my feelings. This is total freedom," said Saad al-Masoudi, a Karbala resident.
But other mourners in the procession felt things had changed for the worse.
"Today is not a good day," said Mohammed Hussein Fadel. "I would have preferred Saddam over the American conquerors... At least Saddam was a Muslim." [nice display of religious bigotry]
The focus of the celebrations is the gold-domed shrine of Imam Hussein in the centre of Karbala.
This year's event coincides with the growing dominance of Shias in post-Saddam Iraq - leading to fears that disgruntled Sunni militants may target the celebrations.
To prevent this, Karbala has been ringed by security forces - with Polish soldiers policing the town's entry points and Shia militias guarding its streets and shrines.