PEERING down into the darkness of the crypt it was just possible to see the two bodies wrapped in blankets. They were not fresh corpses. These had clearly been buried some time ago. Most recently the crypt has served an altogether different purpose from that of housing the dead.

Having prised up a stone panel to gain access through the floor of the vestibule in the Mart Shmony Syriac Orthodox Church, Islamic State (IS) fighters, oblivious of the human remains inside, had been using the crypt as a bomb shelter against US-led coalition airstrikes.

Outside the church in an adjacent graveyard, stone slabs from tombs there had also been removed, enabling them to be used as makeshift bunkers.

From these tombs IS fighters would briefly surface into the open to fire missiles, one of which, a 122 mm rocket, still stood on its improvised angle iron launcher, the surrounding stonework deeply pocked with bullet marks.

Like much of Bartella, picking one’s way through the graveyard and its bunkers is

a discomfiting experience, with wires still lying across the ground that IS once connected to improvised explosive devices meant to kill those who came too close.

It was a little over a week ago now when Iraq’s elite Golden Division Special Forces

and Kurdish Peshmerga fighters battled their way street by street, alleyway by alleyway, house by house into the small predominately Christian town of Bartella. Five fierce days of fighting would follow during which I was able to gain access to the shattered centre of the embattled town.

“This has been a very difficult fight in such a small place,” said Lieutenant Ahmed Matham, a Kurdish Peshmerga officer and member of the Nineveh Plain Protection Units, an Assyrian Christian militia. Matham was one of the unit’s officers leading his men in the street fighting and the retaking of Bartella’s church.

“Daesh used many tactics including truck bombers. Inside the houses there are many tunnels that go from building to building,” he explained, adopting the commonly used Arabic acronym here for the IS jihadists.

So far it’s been established that the jihadists dug a 10 km-long network of tunnels under Bartella, with food and weapons stores. Eight IS fighters, Matham says, held out to the bitter end in the church, all of them fighting to the death.

“Those who wanted to die fighting or blow themselves up did so, they all died,” the young Peshmerga shrugged, as we stood inside the church vestibule just a few feet from the manhole that led to the blackness of the crypt and its corpses.

A large portion of Bartella has been mined and has become a booby-trap maze.

“There were many bombs right here inside the church,” our disposal teams had a tough job defusing them and for sure there must be many, many more across the town we have yet to find,” Matham continued.

Inhabited by Assyrians since the first century, Bartella is one of the oldest Christian towns in the world and its ancient history holds a special place in the hearts of most Middle Eastern Christians. It was home to some 20,000 people until the summer of 2014, when they fled IS’s lightning strike across northern Iraq. It is said that when the jihadists took over cities and towns like Mosul and Bartella, it was the first time in 1,600 years that the church bells fell silent. Those few Christians who remained were given a simple harsh choice: convert to Islam, pay a religious tax, leave or be killed.

Like other minorities Iraq’s Christians have been a particular target of IS violence and its community subjected to enslavement, ethnic cleansing and murder among many other crimes and atrocities.

The town too sits barely nine miles from Iraq’s second largest city, Mosul, the ultimate objective of the current military campaign to end IS’s rule in the capital of its self-proclaimed caliphate.

“We regard this as being in Mosul, because a long time ago Bartella was a small neighbourhood of Mosul, so we can basically say we are inside Mosul now, we are very close,” Matham explains as we crunch our way across the broken masonry and glass of the church aisle.

Outside, the brief rattle of machine-gun fire is a sharp reminder that IS has only withdrawn a short distance and that some of its snipers are still operating in the town, using the labyrinth of tunnels many of which remain undiscovered and riddle the countryside east of Mosul.

It is the same story in many largely liberated areas, with IS managing to leave behind prowling snipers and suicide bombers, men who are bent on killing as many soldiers as they can and have no intention of returning alive.

Over the course of its nearly 28-month reign, IS managed to thoroughly ransack Bartella and most of its antique and medieval artefacts were destroyed.

Inside the church its once ornate lancet windows are smashed, while some of its walls and eaves are smoke blackened and scarred with shrapnel and bullet holes, evidence of the close-quarter fighting that took place here and across much of the town. Christian books have been ripped up and pews have been turned over. Statues and murals almost everywhere have been defaced, one figure on a plinth has had most of its head removed, in keeping with IS rulings on idolatry.

“Our God is higher than the cross,” read IS’s black spray-painted graffiti on the walls.

Getting into the town in the immediate wake of its liberation as pockets of IS resistance continued to fight was a tense undertaking.

Just a short time before our departure two massive explosions came from around the far side of the town sending enormous clouds of dust into the air. Coalition airstrikes perhaps or the dreaded suicide truck bombs that have been widely deployed by IS, striking fear into advancing forces? No-one seemed quite sure.

As we waited nervously before our escorted drive into the town, I came across an elderly Orthodox Christian priest, Father David, who himself was waiting to run the gauntlet into Bartella on a very special mission.

“More than 30 large prayer books and manuscripts are there, we must retrieve them, they are very ancient and important to us,” the grey-bearded priest explained.

Standing alongside Father David as he spoke and also clad in black were Iraqi soldiers from the Army’s elite unit, the Counter Terrorism Service (CTS).

All carried state-of-the-art assault rifles and would act as the priest’s bodyguards in the dangerous drive into Bartella to reach its beleaguered church.

We drove into the town from its eastern approaches at top speed for fear of snipers, passing roadside bombs detected and dug up by advancing Iraqi and Peshmerga troops, some marked with red warning flags.

From the first moments after crossing the town’s edge the vicious no-quarter fighting needed to take Bartella became obvious.

Everywhere buildings had been blasted and ripped apart, larger concrete structures were pancaked one on top of the other. The smell of burning hung in the air and telephone lines and other overhead cables dangled from shot up poles in tangled webs. We passed endless fields of bullet casings strew across the ground and the occasional unexploded shell and shrapnel from car bombs.

At first I thought it strange that there was no trace of civilians or bodies. The explanation I was subsequently told was that those who had remained after the town was taken in 2014 by IS had of course either fled or recently been rounded up and moved back towards Mosul.

There they would join other civilians forcibly being used as human shields against advancing Iraqi and Peshmerga forces and ‘protection’ against bombardment.

Once on foot in Bartella’s backstreets the scale and intensity of the fighting needed to liberate the area really struck home.

In echoes of the Nazi era and the persecution of the Jews, each house along the way had a painted sign at its entrance marked either “property of the Islamic State," “Sunni Muslim," or “Nasrani," a derogatory Arabic word for Christians.

On one back street near an improvised base for the 2nd Iraqi Special Forces (ISOF), Dr Ahmed Hussein, a combat medic accompanying ambulances ferrying the wounded would not give Iraqi casualty figures but said that anywhere between 80-90 IS fighters had been killed. The jihadists too it seems were a “special force", according to Dr Hussein.”

“There were Chechens, Georgians, Uzbeks and Afghans” among them, Dr Hussein insisted.

Other Iraqi soldiers described the worst of the initial fighting as Bartella’s “liberation” got under way, saying the assault began at dawn and included three tanks from the Iraqi Army’s 9th division. The advancing Iraqi units were also supported by attack helicopters as they broke through the earthen berms that once marked the forward line.

One helicopter was hit by IS artillery fire, although the pilot managed to land and crew members were evacuated. IS also dispatched an onslaught of 15 suicide car bombs, and while most were eliminated by tank fire or rockets, at least one hit its target.

“Bartella is the eastern gate to Mosul,” said Major General Maan al-Saadi, speaking alongside the counter-terrorism units inside the town. “Now the road is open.”

Open it might be, but not fully, and continuing reports of IS fighters still lurking in the ruins of Bartella’s southern neighbourhoods took the gloss of his otherwise positive pronouncement. While edging through the town’s shattered streets, I came across Iraqi Special Forces troops who burst into spontaneous song for the benefit of the passing journalists.

“We are the heroes of Golden Division, we will not stop until we reach Mosul,” they chanted.

Liberated Bartella might be, but the scale and challenge of the task in the villages and towns ahead is brought home by the heavy artillery and mortar positions set up no more that 300 yards from the town’s church.

These will now be used to pummel and "soften up" nearby IS positions before the bloody work of liberation continues. Most Iraqi soldiers and Peshmerga fighters admit that the fight for Bartella had been harder than the other villages and towns they have liberated so far. That there will be more battles like Bartella is a given and some are certain to be even worse as they draw nearer to Mosul.

Over the last few days the terrible human cost of liberation from IS has become increasingly apparent. According to UN High Commissioner for Human Rights, spokesman, Rupert Colville, atrocities are on the increase in and around Mosul.

Fifty former Iraqi policemen held captive were killed, while 70 civilians have been shot dead in the village of Tuloul Nasser south of the city.

IS is also said to have tied six people to vehicles by their hands and dragged them around because they were related to a tribal leader battling the extremists. Many civilians too are being forcibly herded in the direction of Mosul.

Those that cannot keep up are killed, like the three women and three girls shot because they were lagging behind as the jihadists were forcibly relocating them to another district south of the city. Their slowness apparently was because one of the girls had a disability.

For now those towns that are free of IS will look in the coming months to their citizens to return. Such a process will neither be quick nor easy. What used to be exceptionally fertile fields on the Nineveh plains have all turned to dust, untilled by human hand for at least two years as the spectre of IS continues to haunt the land.

Bartella’s Orthodox church is still standing, but its has congregation has fled, or was murdered, when the town fell.

“We must never re-live what we have just been through with Daesh,” one Christian militiaman with the Nineveh Plain Protection Units told myself and other journalists who visited Bartella during the fight to free it of IS’s grip. “Our people are scattered, our children are dead, we had to live in tents. Now I want to send a message to my people: Bartella is liberated,” the fighter said. Sadly, it might be some time yet before the same can be said of Mosul.