In June 2014, when the leader of Isis, Abu Bakr al-Baghdadi, declared a global caliphate, he did it from Mosul, Iraq’s second city. Isis rapidly expanded its territory in Iraq and Syria throughout that year, but has since been gradually pushed back, partly due to US-led airstrikes. Losing Mosul now could spell the end of the jihadi group’s ability to control large swaths of Iraq. The long-awaited operation to take back Mosul began on 16 October, involving a coalition of more than 30,000 troops drawn from Iraqi army forces, Kurdish peshmerga fighters and Shia militias, supported by airstrikes from a US-led coalition. Turkish forces are also involved despite Iraqi government opposition. Around 6,000 Isis fighters could be holed up in the city among more than a million civilians. It was agreed that only the Iraqi army would enter Mosul, due to fears its mainly Sunni inhabitants would see the Kurdish and Shia forces as too partisan. After one week, progress was made to the north, south and east of Mosul despite Isis using a variety of defensive tactics. Advancing forces faced roadside bombs, dug-in snipers, fleets of suicide car bombs and oil fire haze. The jihadis also launched diversionary attacks, most significantly in Kirkuk. It was also reported that Isis fighters were forcing people from the countryside into the city to use as human shields. Most progress was made east of the city, where Iraqi forces took the baton from the peshmerga who overwhelmed several villages in the first few days of fighting. A southern push by Iraqi army troops and Shia militias lagged behind the faster-moving eastern axis. Week six: awaiting a breakthrough Anti-Isis forces have effectively surrounded Mosul after more than six weeks of fighting but most observers expect the battle to last into 2017. The only Iraqi units inside the city are making slow progress in eastern districts, where Isis forces are fighting hard in areas where large numbers of civilians are still present. About 70,000 refugees are living in camps mainly to the north-east of Mosul but their numbers could swell if conditions deteriorate further inside the city. Fighting has cut off water supplies for about 650,000 people and the UN has said a siege-like situation is developing. Food supplies have dwindled since Shia militia cut off the main corridor to Isis territory in Syria but the Iraqi government has discouraged them from taking the strategic town of Tel Afar, which may have raised sectarian tensions with its mainly Turkoman residents. Week 14: Iraqi forces near to splitting city A pincer movement by the Iraqi government’s counter-terrorism service is aiming to clear Isis fighters from the east bank of the Tigris. Elite CTS forces seized control of the large Mosul University complex, which Isis fighters used as a base, on 15 January. Meanwhile, other units have pushed north along the river after establishing their first bridgehead on 8 January. The offensive was effectively relaunched at the end of 2016 when troops from other positions were redeployed, along with US special forces, to bolster the main lines of attack in east Mosul. This enabled the CTS to advance after struggling for weeks to move beyond suburbs reached earlier in the operation. Iraqi forces now control the eastern side of three bridges over the Tigris but none are currently operational. All river crossings were partially destroyed by US-led airstrikes aimed at hampering Isis logistics but will now need repairing for an assault on the densely populated west bank where heavy Isis resistance and several more months of fighting likely awaits. Week 20: airport assault drives battle for the west Iraqi government forces took control of most of Mosul airport on 23 February, meeting their first key objective for retaking the western half of the city from Isis. The operation was launched on 19 February several weeks after Iraqi forces took complete control of eastern Mosul. Isis fighters sabotaged the runway last year but Iraqi forces will use the large site as a base to push north into residential districts and towards symbolic locations such as Mosul’s great mosque. A difficult fight is expected in these densely populated, built-up areas where tanks and armoured vehicles will be unable to operate and Isis is likely to use human shields and deploy ambushes and suicide bombers. Up to 750,000 civilians may still be trapped inside west Mosul, with fuel and food supplies dwindling and drinking water and electricity scarce. The UN says about 160,000 civilians have been displaced since the battle for Mosul began in October and aid organisations are preparing for another exodus as the offensive enters its latest stage.