Quote Originally Posted by Rhedd
I do believe they're in the Crusades campaign, as well.

Haven't played that campaign enough to have a battle in one, but they sure look like stone forts on the map, and I know they're permanent.
I have fought a battle with one as Wales vs. the English. The gate faces away from ramp across the moat. So you either brake down the towers or brake through the wall. I choose the latter.

Also got proof that Crusades has stone forts? There are zero on the map and I didn't see any option to upgrade.