From 591 onwards, the Frankish king Theudebert I tried to break into the former Noricum region, and Bavarian settlers entered the area from the Puster Valley in the west. They were however repulsed by Slavic tribes, who, beset by Avar horsemen moved into present-day Carinthia from the east. About 600 the Slavic principality of Carantania arose, stretching along the valleys of the Drava, Mur and Sava rivers. The remaining Celto-Roman population was largely assimilated, jointly challenging Avar and Frankish advance. The name "Carontani" was first mentioned about 700; the lands of "Carantanum" were documented by the chronicler Paul the Deacon (d. 799). The principality was again centered on the historic Zollfeld valley, where the Prince's Stone bears witness to the ritual of the investiture of the Carantanian rulers exclusively in Slovenian language.