“We call this the zero line,” says Mohamad. He points a home-made periscope through the hole in the wall above him. When he brings it back down he confirms it. “Assad’s soldiers are only ten meters away.”

In Aleppo’s Salaheddin district the front line runs straight through houses, through shops, through all the places where people used to live and work and where children used to play in the streets. To reach the “zero line” we clamber through holes blasted in apartment walls and scurry in the darkness through homes left abandoned and still cluttered with the detritus of everyday life. “We sleep with rats running around our heads here,” says Mohamad. Some of the people in Salaheddin left in such a hurry that they didn’t even pause to pick up their identity documents. They have little to come back home to now.

The enemy is so close here that they could almost fight hand to hand. They can hear each other even if they rarely catch sight of each other. “We shout ‘Allahu Akhbar’ to them and they shout Assad chants back at us,” says Mohamad.

The rebels are taking the ground here inch by inch; Salaheddin has been a front line for almost a year now. The prize they are aiming for is a government artillery base just fifty metres away. It’s from there that the regime pounds the city’s civilian areas with mortar fire and rockets. Once they take that, the rebels say, they can finally push Assad’s troops out of Aleppo.

In the next room Mohamad shows me the workshop where he makes Molotov cocktails from juice bottles filled with heavy black oil. He loads one up and lights it, and then flings it out of the window towards the regime soldiers. It doesn’t explode; the oil is too black and too heavy to ignite. But this is what the rebels are forced to fight with here—homemade explosives and ancient guns. Another rebel shows me his hunting rifle: made in Russia in 1955.

Mohamad is seventeen years old and he is getting his first taste of combat in Salaheddin. But he is learning the tricks of insurgency warfare from a veteran. In the street behind the apartment block where Mohamad makes his weapons, Abu Shahoum shows him how it should be done. “These are never going to work; the oil is too heavy,” he says, lighting one of his Molotov cocktails and throwing it on the ground to demonstrate. Abu Shahoum is thirty-five, a Syrian who served in Assad’s army, joined the jihad against the US forces in Iraq in 2003, and returned to his home country only to be arrested by the security services and imprisoned for four years.

When he was released he worked as an electrician, but when civil war erupted in his home city he left his job and joined the rebels. “War is better than that prison cell,” he says. The scars covering his lower legs tell the story of the beatings and torture he endured while he was incarcerated.

More than three hundred Syrian jihadists were arrested and imprisoned by Assad’s security forces when they returned from Iraq. “The group we fought with there was banned by the regime,” says Abu Shahoum. “They accused us of plotting to destroy Syria but that was never the case. We went to Iraq to help our Muslim brothers because the Americans were occupying the country. We knew that Saddam was a dictator but the occupation was something worse.” Most of those prisoners were released when the uprising started, instructed by the security forces to let their friends know that Assad would reform the government. “We’ve had forty years of this regime,” Abu Shahoum laughs. “We knew that was a lie.”

He says that Syria is a different type of war to Iraq, a harsher and dirtier war. “The Americans only attacked the military bases. It was an organised war. But here Assad’s soldiers are targeting civilian areas.” More have responded to the call of jihad here, too; Abu Shahoum says that he has fought alongside Spaniards, Chechens and Bulgarians on the frontline. “There are too many foreign fighters here,” he says.

And of course there are the foreigners fighting on the other side, too. The rebels in Salaheddin say that for the past four months they have heard soldiers on the regime’s side speaking in Persian, or in Arabic with Lebanese accents. “The Iranian soldiers and Hezbollah are professionals,” says Abu Shahoum. “I don’t believe that the Syrians who are fighting on the government side really have the heart to kill their own people. They have to bring these foreigners in.” One month ago the rebels were entering a factory in Salaheddin when they came face to face with fifty fighters from Iran’s Republican Guard, dressed all in black with pictures of Ayatollah Khomenei printed on the backs of their shirts. A firefight ensued; eight rebels and fifteen Iranians were killed. “They are professionals but they still need to come and train with me,” smiles Abu Shahoum.

It is pushing forty degrees in the afternoon heat of Salaheddin. Inside the apartment blocks the air hangs so thick that it is difficult to breathe. Sweat drips down my face and into my eyes as I follow the rebels up and down the dark stairwells, sprint across sniper alleys and clamber through the roughly hewn entrance holes. But it is Ramadan, and for the next month most of these men will do this every day without any food or drink. They tell me that it’s easy; I can’t believe them. After just half an hour I am desperate for water. “Assad’s soldiers know that we are fasting, and that we all eat together at sunset,” says Abu Shahoum, “and they are taking advantage of that.” During Ramadan, Salaheddin’s fiercest fighting starts at Itfar. The day before, two of these rebels’ comrades had been killed as they ate.

But this unlikely band of comrades—17-year-old Mohamad alongside veteran jihadist Abu Shahoum—is pushing onwards regardless. They all tell me that their faith spurs them on, and that two years of relentless war in Aleppo has brought everyone here closer to Islam. But it is especially true for the young men fighting with the rebels. Once Syria’s war is over maybe they, like Abu Shahoum, will go to join the jihad elsewhere. “They have seen how the foreign fighters came here to help them,” says Abu Shahoud. “So because of that you will find Syrian boys on other frontlines in the future.”