and
Are both pretty close. Close enough, so you both win and get to think of new questions!
So what I had in mind was herding pigs into the tunnel under the wall and setting the backs of the pigs on fire. They'd also pack other stuff in there as space allowed and sealed it of a sorts to make an oven, and the fat builds up and burns hot for a long time. The writer I recall spoke about how loud they squealed... Pretty brutal shit. Anyway, it weakens the joints and some of the blocks in the foundation causing them to crumble into the weaker tunnels and a whole section of wall will come down and you just go over the rubble. It's fairly easy to repair too once you take the city/castle/fort/etc.
Wanna say I recall reading about this being used by or against Saladin (the Great?) in the Crusades and it going back as far as Rome, maybe farther. It's a pretty simple technique but gunpowder likely made it obsolete. I'm sure it's limited to certain size walls and I bet it works better on some construction than others, but yeah, makin' bacon has been used to bring down walls.
Siege warfare was some nasty shit, particularly for the besieged, where they've gone on for years.