Millions of Shiite Muslim pilgrims, many on foot, visited shrines in the Iraqi city of Karbala on Wednesday in spite of the threat of Islamic State violence against them. IS and its precursor organization, al Qaeda in Iraq, have frequently attacked such gatherings; they consider Iraqi Shiites supporters of the government.

The pilgrimages that took place this week is known as Shabaniyah and marks the birth of Imam Mehdi, a revered Shiite saint. Pilgrimages take place throughout the year to mark the births and deaths of Shiite saints and culminate in size with the festival of Ashoura, which commemorates the death of Imam Hussein.

The processions were banned under Saddam Hussein's government, which considered them political as well as religious manifestations. After the US invasion in 2003 the main route leading south from Baghdad to Karbala was for a time known as the Highway of Death — a reference to the frequent attacks on pilgrims, as well as attacks on US troops in the area, by supporters of the former government and AQI. IS has threatened to attack both Karbala and the nearby city of Najaf.

The mixed sectarian makeup of many of the towns and cities that surrounded Baghdad have long made them a flashpoint for violence, particularly between 2006 and 2008, which is so far the height of Iraq's smoldering post-Saddam civil war.

Pilgrims began walking the 80 miles between Baghdad and Karbala earlier this week. Early on Monday, a suicide attack on an army base in Karbala left at least 42 dead.

Pilgrims also converged on Karbala from other cities, some even further away. They said they were undeterred by the threat of violence.

"When I was born, my father and grandfather were walking yearly in this anniversary," Abbas, a 60-year-old retired high school teacher undeterred as well by the 110-degree heat, told Vice News.

He was passing through Baghdad on his way from Baquba, about 35 miles northeast of Baghdad. "People have walked for ages."

Jassim, a 14-year-old high school student, sported a pair of earphones connected to a smartphone as he walked.

"It is happiness to become a martyr at the hands of the terrorists," he said, referring to IS.

An Iraqi security official said that thousands of government security forces had been deployed along the route and had carried out preemptive raids in the preceding week to root out possible attackers. The forces included a mix of remnants of the Iraqi national army, local police forces, and members of the Hashd al Shaabi, a conglomeration of militia groups that have taken the lead in the fight against IS in the wake of the Iraqi army's near collapse.

Jabbar Karam, a general in the Iraqi army whose forces were recently deployed from Anbar province to Babil province, said there had been no violence along the road during the festival. The pilgrimage route passes through Babil, and waystations where travelers can rest and eat line the highway. The supplies are often donated by local residents.

"There have been no attacks," Karam said. "It is stable in our area of operations."

Karam's men had been deployed specifically to Mahmoudia, a city that was once a haven for AQI, as well as nearby Yousifia. The cities lie between the highway and the border of Anbar province, where IS has surged in recent months. Though Iraqi government officials promise an offensive against IS in Anbar, much of their strategy appears to center around containing IS there.

The safety of the pilgrims highlights the increasingly different realities in different parts of Iraq. Despite the calm in Babil province and along the pilgrimage route, tens of thousands of refugees from Anbar remained trapped 50 miles away, unable to cross a bridge that that would allow them to travel into Baghdad province, the last such route not controlled by IS or blocked by the Iraqi government.

The fight to secure the road between Baghdad and Karbala has been a long one, and led to accusations of forced displacement. Last fall, the Iraqi government forces took over the city of Jerf al Sakr, one of the closest points IS had reached approaching Baghdad from the south and another city along the pilgrimage route. Residents of that city say they have been largely unable to return, prevented by pro-government militia forces stationed there.

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