Well, huh. So I think I've discovered something new. Did people know invaders can leap straight up? I thought general knowledge was that invaders climb a wall first and then mantle diagonally.
I built two animal watchtowers, unfortunately close to each other. One was a single tile pedestal supporting a 3x3 watchtower. The other was a 3x3 pedestal supporting a 3x3 watchtower. All rough logs. Two tiles gap between platforms. Each 3x3 'platform' is 4 fortifications in the cardinals and and 4 walls at the intercardinals. No roof. Chained cat and chained goose. Stupid me, I forgot the goose could fly up a z but it mattered not. Let's call them pedestal tower and block tower.
They uncovered a massive warwolf (Fortress Defense race - larger than dwarves, very fast) ambush. I watched what happened twice - the warwolves spawned near the block tower and raced right for it. Both times, about 4 ww's arrived and scaled the intercardinal walls (wall on top of a wall) and ignored the fortification-on-wall face. They climbed to z+2 then down in and killed the goose. The killer climbed back out diagonally to the top of the wall, the others hopped to the wall closer to the pedestal.
At this point I thought, crap, I built them too close - they're simply going to leap across to the roof of the pedestal platform. On first viewing, I thought this happened but wasn't certain. It was the 3rd day of Autumn luckily, so I simply savescummed to watch again. Using ".", what I saw actually happen is that they scaled down the wall-on-a-wall to the ground, moved one tile over, then leaped straight up to catch the pedestal platform wall at z+1 above them. I expected them to move in next to the pedestal to climb it then mantle diagonally up a z. Again, all 4 lined up to leap up to the walls above them, totally ignoring the fortification face. From there they climbed to z+2, dropped down into the center, and killed the cat.
So in two runs, they totally ignored the fortifications path when scaling, which lends some evidence to your viewpoint. Next experiment I'm going to:
- place floors on the blockhouse jutting out from the roof of the walls at z+2 to make that path impossible, and see if that forces a path through the fortifications.
- make pedestal platforms with 2 and 3 wall high pedestals to see how far up they can leap (or, to see if they use the diagonal mantling)
A pity that the goblin army before this spawned on the other side of the map, would be nice to be certain goblins behave the same way.