Walls & mountains

Been enjoying the game a lot. Got my first town to tier IV today. I built it next to a pretty steep mountain. Had a lot of raids coming from the east, where there was only a small gap between the mountain and a lake. Thought I’d build a wall there, anchored on those two terrain features. I flattened some terrain so I could build the wall all the way up to a spot where the cliff was too steep to be pathable.

However, when the next raid came, they just walked right around the end of the wall. Frustrating! Given that it would be extremely difficult to build the wall over the mountain, it seems my only choice if I want to build a defensive wall is to build it around the entire mountain? That seems silly. I ought to be able to use the steep terrain as a natural barrier. Thanks.

p.s. It’s unclear to me if the lake works to anchor the other side or not, because the raiders didn’t try to go around that way.