QARAQOSH, Iraq—The church’s interior has been blackened by fire, and the altar has been vandalized. ISIS graffiti has been smeared on the walls, and songbooks lie burned on the ground. But the two priests, undeterred, make their way through the nave of the Church of the Immaculate Conception, climbing the narrow stairway to the mezzanine where the organ has been smashed, and emerge on the flat rooftop next to the belfry.

Here, the tolling of the bell of Iraq’s largest church once summoned 3,000 people to prayer on Sundays. Now the belfry is disfigured by cannon fire and the bell itself is gone, snatched from its chain.

Without hesitation, the priests climb on top of the arched roof running along the spine of the building. They are followed by a handful of men in military fatigues. A makeshift cross—two pieces of plywood strung together with copper wire—quickly follows, and the men begin feverishly to pile up stones to create a simple foundation.

Shots ring out nearby, and mortar rounds crash down a few hundred feet from the church, but within minutes the cross holds firm. Ecstatic, Father Majid and Father Amar burst into song, and the hallelujah rings out in Aramaic, the ancient language that links Iraq’s Christians to the genesis of their faith.

“I’m very happy now that we are able to return to our church,” says Father Amar after climbing back down from the roof, visibly shaken by emotion.

For over two years the Christians of Qaraqosh, Iraq’s largest Christian town, had been deprived of their place of worship. After ISIS stormed into Mosul in June 2014, the militants quickly turned their sights on the surrounding towns and villages, home to the majority of Iraq’s Christians. By August, they had taken Qaraqosh, forcing its 50,000 inhabitants to abandon the town.

But Father Amar’s joy at returning to his native Qaraqosh is tinged with sorrow about the destruction that surrounds him.

“Its very hard for us to see our town like this. Everything is damaged. Do you see that the bell of the church is missing? They destroyed it. Why? I don’t know,” says Father Amar, a middle aged man clad in black and wearing his clerical collar.

The Syriac Catholics worshipping in the Church of the Immaculate Conception have close links to the Vatican. Most Christians in Iraq are Assyrians, and still speak Aramaic, the language used by Jesus as he proselytized 2,000 years ago.

The Christian heartland lies in the north of the country, roughly tracing the boundaries of the ancient Assyrian empire, and Qaraqosh is one of a string of settlements in the Nineveh plains near Mosul that trace their origins back to the dawn of Christianity.

Since Islamist terror spread throughout Iraq in the wake of the U.S. invasion in 2003, the number of Christians has dwindled from around 1.5 million to roughly 500,000, perhaps even less. The rise of ISIS delivered the latest blow to the community.

With the campaign to rid Mosul of ISIS now under way, the jihadists are slowly being flushed out of the surrounding towns and villages and Nineveh’s Christians, most of whom sought refuge in the autonomous Kurdish region that managed to hold off ISIS, are looking forward to going back home.

“Of course we will return and rebuild it,” says Father Amar with emphasis.

But first, the jihadist menace needs to be fully vanquished in Qaraqosh, and that hasn’t happened yet.

The task to liberate Qaraqosh fell to the Iraqi army’s 9th Armored Division, which is helped by a small Christian militia known as the Nineveh Protection Units.

Equipped with U.S.-supplied Abrams main battle tanks, the 9th Division reached Qaraqosh on Oct. 19, but found the going tough against an elusive and fanatical enemy. ISIS launched a series of suicide car bombs against the army, and shifted positions in tunnels to attack unexpectedly.

Losses have been mounting. According to Major Mohammed, who heads the field hospital a few miles further back, 18 soldiers have lost their lives in Qaraqosh, and around 80 have been wounded.

Until now, the outskirts of town facing Mosul have not been cleared, and sniper fire rings out from areas that were thought safe. Given the army’s vast superiority in manpower and equipment, the failure to secure the town raises questions about its performance.

In an MRAP (mine resistant ambush protected vehicle) near the southern rim of the city, Maj. Fuad Jassem sits at his radio to receive information coming from units throughout the town. A voice crackles over the airwaves. It is a tank commander, who has just come under sniper fire. He requests permission to shift his 60-ton war machine to a safe position instead of engaging the enemy.

Near the warehouses where the sniper was spotted, crews lounge next to their armored Humvees, warning off visitors from passing by on foot.

The Iraqis say inadequate coalition air support is a reason for their sluggish progress.

“Sometimes we see Daesh [ISIS] convoys come into the town, but the coalition does not bomb them,” says Maj. Jassem.

Inside the Church of the Immaculate Conception, the two priests are too caught up in their emotions to concern themselves with the slow progress of the army and the Christian militias.

“We are so happy to return to our church,” says Father Majid, who can barely keep his eyes from welling up.

In the spacious courtyard next to the church, where the Christians of Qaraqosh used to gather for religious festivals, the jihadists set up mannequins for target practice, and empty cartridges litter the stone floor. According to Maj. Jassem, ISIS stored weapons and ammunition in the church, knowing that it would not be bombed by the coalition.

As if at an excorcism, the priests and militiamen gather to light candles and place them on the altar. Then Father Amar and Father Majid sing again, and their voices echo through the nave, for a moment dispelling the gloom that hangs over these sacred precincts.