OK. So, the basic rules for birthright castles are fairly strait-forward: A castle has a level rating from 1 to 10. The higher the level of the castle the better - the more units it requres to besiege it, the more troops it can contain in its barracks, the more it costs to build (i forget the exact numbers in each of these cases). A castle's level can be higher than the province it's in, and it protects the whole province from attack (unlike, say, a fortified law holding).

But!

the details seem pretty scare. In my campaign the two castles most commonly visited are Blacktower Castle in Roesonne, and Castle Aglondier (?) in the Free City. I've got maps for both of these from the player's secrets, but no clue as to what level they actually are. Although they're both reasonable castles, I can only assume that those in larger countries and the Imperial City must dwarf them.... and when building a castle from scratch, what kind of fortifications can you expect to include? How many walls, moats, guards and artillary per level?

What do you guys think?