We all know that some Provinces produce unique units that all factions can produce. Some examples: Lithuanian Cav., Trebizond Archers, Spanish Jinetes, Genoese Sailors, Bulgarians Brigands. ect...but a few got by me right under my nose. For example: the Vikings (housecarls), they can be built to whom ever controls the province of Saxony. I, for one, didn't know that.