Bustan al-Qasr is the last remaining crossing point between the rebel and regime-held sides of Aleppo. Snipers are rife and the atmosphere tense, yet hundreds are forced to use it every day to get to work, to study and buy food.

"Today, at about midday, I treated someone who had been shot in the arm," Sam tells me. "He was a child, they usually are. I think that the snipers are aiming for kids, just kids."

Sam, crouching behind sandbags at the Bustan al-Qasr crossing point, is the only doctor on hand to treat those targeted by the snipers.

He is 25, speaks in an urbane North American drawl and has humorous eyes twinkling above his surgical mask.

He is the son of Syrian exiles who settled in Canada. "I was in the final year of my studies to become a cardiac surgeon," he tells me.

But then he felt that he had to come here. Now he sleeps in a room in the field hospital where he works. And in his time off, he comes to Bustan al-Qasr to wait for the snipers to open fire.

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The pavement he sits on is dotted with dark brown blood stains.

"On average I treat about 10 people a day, every single day, but Fridays are always the worst," he says. "Yesterday about 30 people were shot here."

Everybody reacts differently to the sound of the sniper's bullet.

When shots ring out, the sea of people in the marketplace parts as most people press themselves against the walls of the buildings - as if, somehow, that will save them.

But the fatalistic ones just carry on walking straight down the middle of the road in a gesture of defiance.

"Sometimes they just fire in the air, to scare people," I am told. But sometimes they do not - Sam's work bears witness to that.

The frenetic energy of Bustan al-Qasr's marketplace is super-charged with fear.

"At first we stayed away," a market trader tells me. "But then we started coming back. What else can we do? We have to live."

Sara is an activist and a student and she runs the gauntlet every week. Her home is on the rebel side of the city and she crosses over to pick up her notes from the University, which is in the regime-held part.

During exams, she crossed almost every day in her determination to do well. "One day I crossed in the morning, and by the time I came back 15 people had been killed there," she says.

She did pass her exams but she is disappointed with her marks. "I did better last year," she tells me. "No wonder," I reply.

And many families in wartime Aleppo can only buy food if they cross over into opposition-held territory.

Until recently, the checkpoint was controlled by a group of rogue rebel soldiers who tried to extort money from the already desperate people using it.

Image caption Buses and sandbags are used to try to protect people from snipers

The last time I came to Bustan al-Qasr they tried to arrest me and confiscate my camera. But then a sniper opened fire. In the confusion, I escaped.

Now it has been taken over by Ahrar Sureya, one of the city's largest rebel brigades. It is progress for the people who use the crossing point, but also a sign of how fluid and unstable Aleppo's testosterone-charged local politics has become.

This is a city of fiefdoms. Last week Bustan al-Qasr belonged to the criminals. Today it belongs to Ahrar Sureya. And next week, who knows?

The rebels take me to meet Abu Yassin, a senior official in the rebel-held part of the city's Sharia Court police force, who is now in charge at Bustan al-Qasr.

On a corner where the main street meets a side road he points to the buildings where the snipers are stationed, in a government-owned tower block, in an apartment building, in a minaret.

"There are 72 snipers aiming towards us," he says. "And they only ever shoot at civilians."

Some people in the rebel areas want the crossing point closed altogether. Those at Friday demonstrations here no longer call for democracy, or freedom, or human rights. They want the complete dismemberment of this already fractured city.

Image caption A young boy holds up a placard calling for the crossing to be opened

And while closing Bustan al-Qasr might stop regime informants coming into the rebel side of the city, it would be disastrous for many.

It would mean failure for Sara, and maybe starvation for the families on the regime-held side. Because however chaotic, however deadly, Bustan al-Qasr is a lifeline.

It is the last artery connecting a divided city and the only choice for many people.

And the mass of human beings who throng around it - Sam in his field clinic, Sara with her lecture notes and the market traders in the sniper's sights - tell the real story of Aleppo's conflict: one of people trying to carry on with their lives amidst a war they never chose.

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