Hi DEB8 - each level of castle has progressively more destructive towers built into its basic structure. So the walls of a keep have arrow towers, a castle will have some arrow towers and some ballista towers, and a citadel will have some arrow towers, ballista towers and catapult towers. IIRC a fortress also has some gun towers.
The easy way to check it out is to open up the Map Editor feature and take a look at the maps in one of the castle groups - that will show all the various towers in any particular level![]()
Bookmarks