I was going to enter this in the Siege weapon category, but it's really more of a siege tactic than a weapon, so Miscellaneous it is!
the wall, all is quiet here, at least on the surface...
the tunnel under the wall
the men about to burn the wooden supports, caving in the tunnel, and collapsing the wall. Mocpages
Good job but I think it would have been better if there were troops attacking the wall while the others are digging. Interesting MOC because it's historically accurate.