On 22 May​ , Ahmed Mohsen, an unemployed taxi driver, left his house in the Islamic State-controlled western part of Mosul to try to escape across the Tigris to the government-held eastern side of the city. He and his mother, along with ten other people, carried rubber tyres down to the river: most of them couldn’t swim, and they planned to tie them together to make a raft. The siege of Mosul was in its seventh month and Ahmed was both desperate and starving: he and his mother were living on handfuls of wheat they cooked, though he said it made him feel sick. His friends believe that lack of food made him light-headed and led him to risk crossing the river. ‘Even if I die in the river,’ he told them, ‘it will be better than living here.’

IS snipers were shooting people who tried to leave. Their commanders calculated that holding the civilian population hostage, as human shields, would deter Iraqi government troops and the US-led coalition air forces from using the full extent of their firepower. This strategy had worked, to an extent, during the siege of east Mosul, which began on 17 October; it was three months before that part of the city was captured. But by the time the assault on west Mosul began on 19 February there was little sign of Iraqi or American restraint. As the bombardment intensified, the only plausible escape route for Ahmed was across the Tigris between the Fifth and Sixth Bridges, both of which had been put out of action by coalition airstrikes. He had already seen IS snipers kill three people who’d tried to cross and his luck was no better: a sniper shot him in the back and killed him, along with nine other members of his party, before they had even put their tyres in the water. Only one man, a good swimmer, got across to the other side. According to people living in houses overlooking the riverbank, Ahmed’s mother stayed beside his body for three days. Nobody dared to go to help her because they were afraid of being shot; on the third day, they say, they could no longer see her or the body of her son. They were probably thrown into the river, like hundreds of others.

I had​ got to know about Ahmed in an indirect way, two months before he died. After IS captured Mosul in June 2014 it became difficult for journalists or anybody outside the city to talk to people living under its rule. IS did everything it could to seal off the population from contact with the outside world. It blew up mobile phone masts, banned the use of phones and executed anybody caught using them in the few high places where there was reception. You could always interview people who had fled IS territory, but this wasn’t a satisfactory way of gathering information: refugees from Mosul arriving in Iraqi government or Kurdish-controlled territory were at the mercy of local military and civilian authorities and had every incentive to denounce IS as demonic, to dispel suspicions that they had been collaborators or members. Mosul is a Sunni Arab city and Shia, Kurds, Christians and Yazidis suspect Sunnis in general of colluding with IS. ‘I have never seen such terrified people in my life as a group of young men who had run away from Mosul waiting to be vetted by Iraqi security to see if they were former IS fighters,’ a human rights worker in a camp for internally displaced persons 15 miles south of Mosul told me. ‘One day I saw two men of military age walk into a tent for questioning. They were carried to the camp hospital on stretchers two hours later covered in blood.’

As the assault on west Mosul gathered pace, the IS strategy of isolating people behind its lines started to falter. The Iraqi government brought in a mobile phone mast mounted on the back of a truck and put it up at Nabi Yunus, the Tomb of Jonah, a shrine that IS had blown up as heretical in 2014, but whose ruins remain the highest point in east Mosul. Phones in the west of the city started working again and IS was too busy defending itself against army incursions to hunt down civilians talking on their mobiles. I knew someone who lived on the east bank of the Tigris: he found he was able to speak, over a poor connection, to relatives and friends in the IS-held territory on the other side of the river.

Ahmed Mohsen, trapped with his mother inside the old city of Mosul, was 31 years old. His father was dead; he had a married sister living nearby and a brother who was a refugee in Germany. I asked questions through an intermediary he trusted and he gave detailed answers about the situation in west Mosul. ‘Dozens of civilians are killed every day, including children,’ he said. ‘Yesterday, two children were killed by a mortar shell of the Iraqi army coming from the eastern part [of the city].’ He derided American and Iraqi government claims that they were using ‘smart artillery’: the incoming fire, he said, was ‘stupid’ and indiscriminate. It became clear, as the assault on west Mosul went on, that the Iraqi and US generals were using their massive firepower more freely than they had in the east. The Americans had expected the siege to take two months from start to finish; by March it had already gone on for five months, with the heaviest fighting still to come in the alleyways and closely packed houses of the old city. By then, according to US Central Command, 774 members of the Iraqi security forces had been killed and 4600 wounded. The rules were changed: units on the ground could now call in airstrikes or artillery fire at will to destroy a building if they believed they had spotted an IS sniper operating from it. Alongside attacks from the air, Iraqi Federal Police and the Emergency Response Division, both heavily armed but inadequately trained, used artillery and rockets – none of them accurate – to pound the densely inhabited buildings where, even in the final weeks of the siege, 300,000 people were hiding in stairwells and cellars. Looking later at the ruins of central Mosul, I could see where shells and rockets had knocked sections off buildings and where bombs had turned a whole block into a mound of broken bricks. ‘Iraqi forces and the US-led coalition used imprecise, explosive weapons, killing thousands of civilians,’ as an Amnesty International report, At Any Cost: The Civilian Catastrophe in West Mosul, puts it. By the end of March, civilians behind IS lines were being killed in large numbers by shells, rockets and bombs. They were also beginning to starve. ‘People in our neighbourhood,’ Ahmed told me, ‘are searching in the garbage to find something that can be eaten to take it to their children.’ Vegetables and fruit had disappeared from the markets that were still open; Ahmed and his family had stored some flour and rice, but wanted to keep it as a final reserve for the children of their extended family.

The coalition had a lethally over-simplified list of signs visible from the air which indicated that a building was being used by IS. Ahmed had a tarpaulin draped over part of his house as a sunshade, a practice fairly common in Mosul, where the temperature in summer often exceeds 45°C. Disastrously, similar tarpaulins were being used by IS to cover alleyways or courtyards so that coalition surveillance aircraft couldn’t see armed fighters moving from house to house. The coalition had made an announcement that anybody using such a covering would be attacked as an IS target, but few in the west of the city had heard the news. On 28 March, a coalition drone flew over Ahmed’s house and dropped a bomb. It fell on a corner of the building, near a water tank, bringing down a wall near where Ahmed was standing. ‘I didn’t lose consciousness,’ he said. ‘After a few moments, I realised I was injured. I partly walked and partly crawled to a small temporary clinic nearby, but they couldn’t treat my leg properly.’ The medics said he needed surgery but they didn’t have the equipment for an operation and could give him only bandages. When we spoke to Ahmed again, he was back at home, in bed, crying as he talked because of the pain in his injured leg.

When I wrote about Ahmed for a newspaper report, I changed his name and age and avoided any detail that might identify him to IS, of whom he was terrified. I hoped to meet him when the siege was over, though I could see from his own account that there was a good chance he wouldn’t survive. Mosul had been a dangerous place for a long time. I was there when Kurdish ground troops backed by US airstrikes captured it after the US invasion in 2003, and I watched as order collapsed within hours, as looters ransacked government buildings and Sunni clerics called from the minarets for people to man the barricades. Over the next 11 years, neither the Americans nor the Shia-dominated Iraqi government ever won full control over the city, and in June 2014 a few thousand IS fighters unexpectedly took charge, defeating an Iraqi government garrison of at least twenty thousand men. At the time, Ahmed, who came from a poor family, was driving his taxi between Mosul and Baghdad, a journey of about four hours. His friends say he was a friendly and generous man, who liked talking to passengers and who took great care of his car, of which he was proud. He didn’t own it outright, but had bought a share in it and was saving up to buy the rest. When IS overran Mosul, travel to government-held areas was still just about possible and Ahmed went on driving to Baghdad. But a few months later he was arrested by IS, accused of helping members of the Iraqi police and army to escape the city. As a friend of his put it, ‘he stayed in prison for three months and was badly tortured. He would talk a lot about that.’ He was released but could no longer work, and then he was jailed again for a month and a half. He worried about his mother: his brother in Germany was able to send back small amounts to support her but wasn’t officially allowed to work. ‘When Ahmed was freed for the second time,’ his friend said, ‘he sold his share in his taxi and spent the money over the remaining two years of IS rule. Recently, he went bankrupt.’

Despite these disasters, Ahmed and his mother remained optimistic well into the siege that IS rule wouldn’t last much longer and that things would improve. They planned to travel to Turkey, where Ahmed’s brother would meet them. This brother now appears to be the only surviving member of the family; he is trying to get a death certificate issued for Ahmed, which would entitle him to asylum in Germany and allow him to get a job. His married sister has disappeared: she is believed to have been killed in an airstrike, though her body hasn’t been found. This is far from unusual: at one stage, the Civil Defence Corps in west Mosul had just 25 men, one bulldozer and a forklift truck to search for bodies, estimated to number in the thousands, buried under the ruins. They haven’t been paid their salaries by the central government and won’t search for a body unless a relative can give them a clear idea of where it is.

Ahmed was one of Iraq’s five or six million Sunni Arabs, politically the dominant community under the rule of the Ottomans, the British and the Baath Party, though numerically a minority. But since 2003 the Sunni have been on the losing side in a sectarian civil war with the Shia who now control the Iraqi state: in 2006 and 2007 the Sunni were squeezed into small enclaves in Baghdad that one US diplomat described as ‘islands of fear’. IS’s victories in 2014 in Iraq and Syria allowed them a brief resurgence. But the Iraqi government counterattack, backed by American aircraft, wrecked their cities, including Ramadi, Fallujah, Baiji and Tikrit, displacing many from their homes. ‘We are the new Palestinians,’ a Sunni journalist from Ramadi told me in 2015, predicting a future of flight and dispossession. At the time, there were half a million displaced Sunni Arabs in Kirkuk Province who have now been joined by a million people from in and around Mosul.

Most Sunni would argue that they never voted for IS, couldn’t refuse to co-operate without being killed, and were often as much its victims as anybody else. But this isn’t going to save them. Other communities, in both Iraq and Syria, suspect their Sunni neighbours of collaborating with IS, covertly if not openly. Sectarian and ethnic hatred runs deep, especially after such IS atrocities as the Camp Speicher massacre in 2014, when 1700 Shia air force cadets were killed near Tikrit. Fear of IS ‘sleeper cells’ is pervasive: a Syrian Kurdish commander advancing with his troops near Hasakah told me that he his two main problems militarily were the mountainous terrain in which he was fighting and the threat to his troops from Sunni Arab villagers. Some of them waved nervously at us as we drove past, but it seemed unlikely that they would be allowed to stay in their homes for very long. In Iraq, Sunni tribal leaders are expelling ‘Daesh families’ to underline their loyalty to the Iraqi state. Sectarian and ethnic cleansing is sweeping away Sunni communities across northern Iraq and Syria.

The battle for Mosul – where IS had declared its caliphate – was always going to be bloody. But the fight was even more destructive than anyone expected thanks to a number of mistakes made by the Iraqi government and the US. IS resistance was stronger and their own forces weaker than they imagined. Haider al-Abadi, Iraq’s prime minister, was convinced that people in Mosul would rise up against IS when given the chance, so as the siege came into operation locals were discouraged from leaving the city. But IS had a well-organised and ferocious security apparatus: anyone who showed signs of resistance was killed. And then there was its military expertise: it defended Mosul with a combination of snipers, suicide bombers, mines, mortars and booby traps. Swiftly moving from position to position, IS fighters inflicted heavy casualties on pro-government forces and minimised its own losses despite its enemy’s overwhelming superiority in firepower. The Iraqi government’s Counterterrorism Service, the division of between eight and ten thousand highly trained men who did the bulk of the fighting in east Mosul, suffered a casualty rate of between 40 and 50 per cent. Losses as heavy as this could not be sustained for long.

After east Mosul was finally won, the strategy for regaining the city west of the Tigris was revised. West Mosul had a larger population than the east – 750,000 compared to the east’s 450,000, according to a UN estimate – and the buildings were more tightly packed and easier to defend: many alleyways in the old city were so narrow that two people couldn’t walk abreast. Already short of combat troops, the Iraqi government and the US-led coalition decided to rely much more heavily on firepower than it had in the first phase of the siege. The Federal Police and the Emergency Response Division played a bigger part in the fighting, using mortars, artillery and rockets. Grad missiles – Soviet weapons from the 1960s – were fired in volleys of forty at a time from the back of vehicles in the general direction of IS-held territory. Locally made rocket-assisted munitions, with warheads weighing between 90 and 140 kg, were fired into what was becoming one of the most densely populated patches of ground on earth. Even before the government offensive began, IS had been forcing people from their homes in the villages around Mosul and busing them into the city. As IS’s territory shrank under the government forces’ onslaught, it compelled civilians at gunpoint to retreat deeper into the IS enclave: snipers killed anyone who tried to flee behind government lines; the metal doors of houses were welded shut; those caught escaping were hanged from electric pylons; survivors speak of 75 or more people being gunned down at one time by IS patrols as they tried to run away.

Nobody knows for sure how many civilians were killed in the city as a whole. For long periods, shells, rockets and bombs rained down on houses in which as many as a hundred people might be sheltering. ‘Kurdish intelligence believes that over forty thousand civilians have been killed as a result of massive firepower used against them,’ Hoshyar Zebari, Iraq’s former foreign minister, told me. People have disputed that figure, but bear in mind the sheer length of the siege – 267 days between 17 October 2016 and 10 July 2017 – and the amount of ordnance fired into a small area full of people. The Iraqi government ludicrously claims that more of its soldiers died than civilians, but refuses to disclose the number of military casualties and has banned the media from west Mosul. On his website Musings on Iraq, Joel Wing gives a figure of 13,106 civilian fatalities based on media and other reports, but adds that ‘the real number of casualties from the fighting in Mosul is much higher.’ The Civil Defence Force, looking only for bodies that relatives have located, is still delivering between thirty and forty of them to the city morgue every day. The UN says that out of 54 residential areas in west Mosul, 15, containing 32,000 houses, were completely destroyed; 23 areas lost half their buildings; and even in the 16 areas that were ‘lightly damaged’ some 16,000 houses are in ruins.

All the people I was in contact with inside the IS-held part of the old city are dead. Ahmed Mohsen was wounded by a drone and then killed by an IS sniper; his mother and sister have disappeared and are presumably dead. I was also in touch with Rayan Mawloud, a 38-year-old businessman with a wife and two children who had a trading company based in a shop in one of Mosul’s markets. He came from a well-off family and his father had a fleet of trucks that used to carry goods to and from Basra and Jordan. When the attack on Mosul began, a friend of Rayan’s says that he spent his savings buying food to give not just to his relatives ‘but also to many people whom he did not know’. Rayan, knowing that his family would probably be shot by IS snipers if they tried to escape, took the opposite decision to Ahmed Mohsen and stayed with his family in their house. It was hit in an airstrike on 23 June, killing his wife and five-year-old son. He remained in the part of the house that was still habitable, but it was hit by another airstrike on 9 July. He was severely injured and died three days later.