I just tried to conquer Nidaros (Norway, in the very north of the map) an the AI had some problems during the battle.
1. My troops couldn´t realy go up to the wall. I think because the round hole only has a very small way where you can go up.
Some of them managed, but only one every 10 seconds, so he got slaughtert immedeately.
2. Lots of the enemy troops got stuck on the other side of the wall and didn´t realy defend themselves when I hacked them down with my Sword.
3. Also the steps in the left of the Gangway up to the wall. (looking from the outside) has an edge on the last step so, the AI can´t use it, I could, but they got stuck there too.
Another "ladder" would be very nice, I had a battle with 430 troops on each side there an it took hours until I got up alone and killed all the enemys stuck in the wall.
All the other Fortresses I saw are wonderfull!