After the barbaric invasion and after the settlement of Slavic tribes, these regions belonged to the surrounding dioceses: Split, Nin, Knin, Krbava and Bosnia, and the area of today's Banja Luka and the entire northern region was part of the Diocese of Zagreb. A rich life of the Catholic Church in this region before falling under Ottoman rule is testified by numerous churches from ancient and medieval times discovered on the territory of the Diocese. The highest concentration was in the Bihać Deanery area.