What began as a tense yet joyful day for Iraq's Shiites, with about a million people chanting prayers and streaming toward a gold-domed shrine, unraveled into the single worst human tragedy since the beginning of the war.
Wednesday's celebration of the martyrdom of Shiite Imam Mussa Khadim, a descendant of the prophet Muhammad poisoned by a Sunni king in the 8th century, was supposed to be a symbol of Shiite Iraq's new political power and freedom, since it was a pilgrimage that was banned under Saddam Hussein. The massive celebration also served to underscore the country's rising religious fervor in the face of so much violence.
But the day that ended with about 800 deaths - most from a stampede sparked by rumors of a suicide bomber, and others from insurgent mortar attacks - was perhaps one of the most painful examples of the centuries-old division between Shiite and Sunni branches of Islam.
At 8 a.m., mortars and Katyusha rockets slammed into two neighborhoods near the shrine, killing 15 and injuring about 30.
An hour later, victims of poison - apparently in the free food and water available along the pilgrims' route - trickled into hospitals, according to Iraq's Health Minister. A leading Shiite politician alleged that 100 people were killed by poison.
Then at 10 a.m., the wave of the tragedy crested and broke. As tens of thousands of Shiite pilgrims poured onto the Bridge of the Imams toward the shrine, backing up at the end of the bridge to be checked for explosives, men in the crowd began shouting there was a suicide bomber, survivors say.
The crowd then surged. Strong men pushed and shoved to get to safety. Children, women, and the old were trampled.
On the bank across from Khadimiya, home of Imam Kadhim's mausoleum, pilgrims unaware of the panic kept piling up at the foot of the bridge, serving as a tragic cork in a bottle.
The pilgrims caught in the middle of stampede began to stack up on the bridge's span. Thousands tumbled over the railings, 50 feet into the murky waters of the Tigris River. Many of the people were unable to swim.
As the Monitor went to press, Iraqi health authorities said at least 700 mostly women and children were confirmed dead in the stampede, and at least 300 wounded. They said the death toll could top 1,000. It was the second most deadly incident at a Muslim pilgrimage; a stampede at Mecca during the Haj pilgrimage in 1990 killed 1,426 people.
"If we had been on the bridge already, we'd probably be dead right now," says Rashad Hanashi, still fighting to hold back tears, who was just moments from stepping onto the bridge when the panic started.
"There were dead women and children all around, I saw that and I began to strike my cheeks and cry. I won't forget this until the day I die," she said.
Ms. Hanashi describes a "mob in a frenzy" trying to get off the bridge, many shouting "suicide bomber" while others said they thought that poison gas had been released on the bridge.
While there is no evidence that anything other than panic and poor crowd control were directly responsible for Wednesday's tragedy, the backdrop of the early morning mortar attack and past Sunni insurgent suicide attacks at Shiite shrines had many pilgrims edgy before the morning attack.
Later in the day, Prime Minister Ibrahim al-Jaafari said he believed panic was sown deliberately. "We smell an effort to provoke a strife and generalize it. There is no doubt that this terrorist operation doesn't differ from the other terrorist attack," he told Al Iraqiya, the state television station.
Iraqi police commandos and unarmed operatives from the Supreme Council for the Islamic Revolution in Iraqi (SCIRI), one of two main Shiite Islamist political parties, were out in force at the pilgrimage selling everything from dates and spices to portraits of Shiite Imams and DVDs.
They frisked most pilgrims for suicide belts at haphazard checkpoints, while police trucks mounted with machine guns patrolled streets packed with pilgrims, some having walked for a week or longer from southern Shiite cities.
Shortly after the bridge stampede - with conflicting reports that Sunni insurgents had spiked free food and water with poison - loud speakers urged pilgrims to only take sustenance from mosques or officials with security badges.
On one side of the the Bridge of Imams is Khadimiya, a Shiite city that grew up around the shrine of Imam Khadim. On the other is the Sunni city of Adhamiyah, a dangerous place built around the mosque of Abu Hanifa, a leading Sunni jurist in the 8th century.
The bridge has been closed for months, separating the relatively safe Khadimiya from its more chaotic neighbor, where many supporters of Saddam Hussein still live. It was opened Wednesday to foot traffic for the pilgrimage, particularly for the residents of Sadr City, a poor Shiite neighborhood.
"We didn't have this kind of freedom while living under that infidel Saddam,'' says Hamid Khadim, a resident of the area grabbing some shade and watching pilgrims stream past. "The life of Imam Khadim was a symbol of the tyranny we've lived under for 1,400 years, but not anymore."
The split between Islam's Shiites and Sunnis came soon after the death of the prophet in AD 632. A dispute followed that centered around who should lead the faithful in his absence - the descendants of Ali, Muhammad's son-in-law and cousin, or the members of the family of Uthman, a companion of the prophet who had married two of his daughters.
To Shiites (which means "partisans," from "partisans of Ali"), Ali was the first of the line of Imams, and his close family ties to Muhammad are seen as a source of spiritual authority. In the early centuries of Islam, wars raged between Sunni and Shiite for both spiritual and temporal power. The Sunnis came out on top.
But the Shiites hung around, a persistent thorn in the ruler's side. Ali's descendant Musa Khadim was the seventh Imam, and while he held little political power during his life, his spiritual authority was viewed as a threat by the Sunni Caliph Harun Rashid, who was based in Baghdad.
Legend has it that upon saying "Peace be upon you, o cousin,'' at the tomb of Muhammad in Mecca, he was followed by Khadim, who said "Peace be upon you, o grandfather."
This enraged the powerful Rashid, because he felt it was a claim of a right to rule due to better lineage, and he eventually imprisoned Khadim for the last 15 years of his life, frequently tortured him, and, according to Shiite legend, poisoned the imam and dumped his body on a bridge not far from Wednesday's tragedy.
Imam Khadim's body was then borne to the cemetery - reserved for members of Muhammad's tribe - by a large procession of his followers and buried. It's on this site that his glittering shrine stands today.
Saddam Hussein, like Rashid, felt politically threatened by Shiite veneration of their imams, and massive pilgrimages like Wednesday's were prevented.
"Rashid and Saddam are the same to us,'' says Ghazi al-Majid, a pilgrim. "He helped stir up hatred between Sunni and Shiites."
A group of women, shrouded in black robes, made their way home past a poster of leading Iraqi singer Khadim al-Soher, pitching for the local cellphone company, and each stooped to pick up a stone and lashed it into the sign as they filed past.
"He's wicked, he's not a good Muslim,'' said one of the women.
• Usama Redha contributed to this report.