@kenny1 Could you give me a pic of the city if available.
@Shmektheshmuck Um how on earth would your army have gotten catapults thought mountains as high and steep as the Himalayas in winter? That's physically impossible.
Instead I'd suggest using human magic. It's weaker than demons, but would be able to handle throwing a few rocks at a thirty foot high wall of compacted dirt (the wall the demons rose to keep the city from being flooded)
@kenny1 magic then.
Only the front vanguard were killed.