AS THEIR fighters swept across northern Iraq in 2014, Islamic State commanders knew their victories would not go unchallenged.

They knew a counter-attack was coming, one backed by air power and armour. They prepared accordingly.

Like other forces before them, they took to the earth, carving out networks of tunnels beneath the urban centres they would be fighting for.

The existence of tunnels is well known to the Iraqi security forces, but complexity of their digging operations continues to surprise the troops uncovering them.

“For two years we observed them. We knew they were digging because we could see them coming out of the ground, but to be honest we didn’t expect it to be at this scale,” says General Bahram Arifassi of the Kurdish Peshmerga.

I’m speaking to him in Bashiqa, 13km east of Mosul, where his troops recently discovered more than 10 tunnels after recapturing the area. He expects there are others here left to find.

“They built the tunnels for two reasons,” he explains. “Firstly, as protection from air strikes. They would hide themselves there and be safe. Secondly, imagine Peshmerga are attacking, entering the village. They could come around them and hit them in the back.

“They had some rooms inside connected to CCTV and they were observing the area from underground. They tried to use that to see where the Peshmerga pushed so they could push from the back.”

The tunnels here vary in length from a few dozen metres to half a kilometre. The builders carved them directly into the rock of Bashiqa mountain and lined those beneath the town itself with timber and metal frames for strength.

They are wide enough for two men to squeeze past one another, and a person of average height could walk through most sections without fear of hitting their head. Some have makeshift hospitals, rest areas, kitchens and weapons storage. Small generators powered lights and ventilation systems — usually just desk fans affixed to the walls.

In the mountain, one tunnel is littered with the hastily abandoned objects of IS fighters — clothes, kitchenware, foodstuffs, digging implements.

One man has written his name and the words “We are surrounded, thank God” on the beams beneath a bunk bed. The tunnel winds about 150m through the rock to the other side of the mountain, where it ends in a camouflaged “spider hole” overlooking the road.

During the Peshmerga attack on Bashiqa a sniper killed two soldiers from this position.

Another inconspicuous hole in the town itself leads six metres underground, turning at right angles every few metres to make each corner a defensive position before popping up inside the living room of a nearby home.

To keep its location hidden from aircraft, the excavators dumped the earth and rock into the other rooms of the house, filling three from floor to ceiling.

“They had used wood and timber, welders, a lot of work there,” says Peshmerga Lieutenant Sherwan Ali Salih. “When I myself went down I was surprised and kind of shocked by how skilful they were.”

He says he doesn’t know how long each one would have taken to construct, but that there are stories that IS paid some locals 4000 Iraqi dinar (about $4.65) per day to work on the projects. Those caught smoking cigarettes were punished with one day’s digging. The remaining labour came from those enslaved by IS. A UN report released in June estimated some 3500 people, mostly women and children, were still held as slaves by IS.

Large excavators were also used. Lt Sherwan says he’s seen two machines, weighing 12 and 25 tonnes respectively, captured elsewhere by the Peshmerga.

General Arifassi says that his men did not find any such machines in Bashiqa, and believes they have been redeployed to Mosul. Even so, as the battle moves on past Bashiqa and into the heart of Mosul, the movement of earth here is not quite over. Plans for the tunnels’ future need to be settled before residents can return.

“Of course we will fill some of them because they are in people’s houses, right in their living room, and beneath houses,” says General Arifassi.

“But, for sure, there are some tunnels we will keep as memorials to the war fighting IS.”

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