It's possible to create bridges that span the moat, and mines that would blow up the wall. Of course, it would need to be weakened first – for example, it explodes after a few turns and can severely injure its own creatures, while the bridges can only support one unit or break after a few turns... Something like that.
The idea of a bridge is interesting :smile20:, but mines would be unnecessary, as catapults already handle this task well. :cool: