Might be a dumb question, but did you research Stone Hail?
Also, the wiki says each catapult increases by 10% the chance of destroying a building in the city you're attacking. Maybe you didn't send enough catapults to make the chance of hitting a building 100%.
yes stone hail was researched and it should have been able to be able to destroy a few levels.
would it not work some of the time if some buildings are at level one
I've looked around a little and it would seem that if the buildings of a city are at level 1 they cannot be destroyed any further. How big was the city? (I mean - could it be possible that there were no building over lvl 1 in this city?)
This is a bit of a late response, but better late than never, right?
Anyway, my alliance and I have been hitting with stone hail on Gela and apparently, no buildings are destroyed if no cats have survived the battle. So you need to have at least 1 catapult alive at the end of the fight to have a chance to destroy a random building