Mosul, Iraq (CNN)Flies buzz around the drying rivulets of blood seeping from the heads of two corpses draped over the hood of a Humvee.
Since Mosul's capture by ISIS fighters in June 2014, Mosul has been a vital stronghold for ISIS.
The largest city under ISIS control in Iraq and Syria, it was the city from which the group first declared the establishment of its so-called caliphate.
Since then, ISIS has gradually lost its other Iraqi cities -- Ramadi, Tikrit and Falluja -- to government forces.
As many as 750,000 people are estimated to remain in Mosul, once a cosmopolitan trade hub of 2 million residents.