Slavic state in Europe, centred at Zollfeld. Together with the indigenous population they were able to resist further encroachment of the neighboring Franks and Avars in the southeastern Alps. In the meantime, the Germanic tribe of the Bavarii (Bavarians), vassals of the Franks, had developed in the 5th and 6th century in the west of the country and in what is now known as Bavaria, while what is today Vorarlberg had been settled by the Alemans. In the northern alps the Bavarians had become established as a stem dukedom around 550 AD, under the rule of the Agilolfings until 788 as an eastern outpost of the Frankish Empire. At that time the lands occupied by the Bavarians extended south to current South Tyrol, and east to the river Enns. The administrative center was at Regensburg. Those groups mixed with the Rhaeto-Romanic population and pushed it up into the mountains along the Puster Valley. In the south of present-day Austria, the Slavic tribes had settled in the valleys of the Drava, Mura and Save by 600 AD. The westward Slavic migration stopped further Bavarian migration eastwards by 610. Their most westward expansion was reached in 650 at the Puster Valley (Pustertal), but gradually fell back to the Enns River by 780. The settlement boundary between Slavs and Bavarians roughly corresponds to a line from Freistadt through Linz, Salzburg (Lungau), to East Tyrol (Lesachtal), with Avars and Slavs occupying eastern Austria and modern-day Bohemia. Carantania, under pressure of the Avars, became a vassal state to Bavaria in 745 and was later incorporated into the Carolingian empire, first as a tribal margravate under Slavic dukes, and after the failed rebellion of Ljudevit Posavski in the early 9th century, under Frankish-appointed noblemen. During the following centuries, Bavarian settlers went down the Danube and up the Alps, a process through which Austria was to become the mostly German-speaking country it is today. Only in southern Carinthia, the Slavic population maintained its language and identity until the early 20th century, when a process of assimilation reduced their number to a small minority. Middle Ages Early Middle Ages: Duchy of Bavaria (8th–10th centuries) Bavarian relationship with the Franks varied, achieving temporary independence by 717 AD, only to be subjugated by Charles Martel. Finally Charlemagne (Emperor 800–814) deposed the last Agilolfing duke, Tassilo III, assuming direct Carolingian control in 788 AD, with non-hereditary Bavarian kings. Charlemagne subsequently led