Are Iraqi-led forces close to victory, or are the militants digging in for a lengthy and dogged war of attrition?
Mosul is ISIS's last major stronghold in Iraq -- and the terror group has shown that it is willing to go to almost any lengths to keep hold of it, using everything from suicide bombs to booby-trapped toys
in its desperate fight.
ISIS has had months to prepare
for the offensive -- building tunnels, constructing explosives, rigging abandoned houses to detonate and plotting counterattacks; reinforcements were reportedly brought in from Raqqa in Syria to help defend the city.
The conflict is "not a conventional war,"
according to Iraq's former foreign minister, Hoshyar Zebari.