My head canon was that they were the cause of the city's destruction. I didn't really have a good story for how or why. Slave revolt? Soldiers with conflicting orders? Evil wizard with a failed scheme?

I had also had an idea that a steel dragon was the ruler of the city but that went nowhere fast.

So, I had a scene and a monster, and nothing to use them for. Maybe some reader will. I'd love to hear their story!