It is not known if the division was territorial (as with the Merovingians) or purely a co-regency (as with the later princes of Benevento and Capua). If the former, it seems to have followed the fourfold ecclesiastic division into dioceses which Theodo had effected. If that is the case, it is most probable that Tassilo ruled the diocese of Passau with his capital there at its see.