MOSUL, Iraq — She survived the first stone that struck her, then the second.

One of the Islamic State group’s fighters bent down and pressed his fingers to the side of her neck to check her pulse.

As her horrified neighbors watched, extremists threw a third stone at the young woman, who was accused of adultery. That one killed her.

It was, for those who witnessed it, the cruelest moment in Mosul’s two-year descent into fear, hunger and isolation. Before the siege, Iraq’s second-largest city was arguably the most multicultural place in Iraq, with a Sunni Muslim Arab majority but also thriving communities of Kurds, Shiites, Christians and Yazidis. Together, they had created Mosul’s distinct identity, with its own cuisine, intellectual life and economy.

But the Islamic State group turned Mosul into a place of literal and spiritual darkness. It began with promises of order and a religious utopia that appealed to some, but over the course of 2  1/2 years, the militants turned crueler, the economy crumbled under the weight of war and shortages set in. Those who resisted watched neighbors who joined IS turn prosperous and vindictive. Parents feared for the brainwashing of their children. By the end, as Iraqi troops besieged Mosul, the militants hanged suspected spies from lampposts, and residents were cut off from the world.