The earliest known inhabitants of the district afterwards called Bavaria were a people, probably of Celtic extraction, who were subdued by the Romans just before the opening of the Christian era, when colonies were founded among them and their land was included in the province of Raetia. During the 5th century it was ravaged by the troops of Odoacer and, after being almost denuded of inhabitants, was occupied by tribes who, pushing along the valley of the Danube, settled there between A.D. 488 and 520. Many conjectures have been formed concerning the race and origin of these people, who were certainly a new and composite social aggregate. Most likely they were descendants of the Marcomanni, Quadi and Narisci, tribes of the Suevic or Swabian race, with possibly a small intermixture of Gothic or Celtic elements. They were called _Baioarii, Baiowarii, Bawarii_ or _Baiuwarii_, words derived most probably from _Baja_ or _Baya_, corruptions of _Bojer_, and given to them because they came from _Bojerland_ or _Bohemia_. Another but less probable explanation derives the name from a combination of the old high German word _uuâra_, meaning league, and _bai_, a Gothic word for both. The Bavarians are first mentioned in a Frankish document of 520, and twenty years later Jordanes refers to them as lying east of the Swabians. Their country bore some traces of Roman influence, and its main boundaries were the Enns, the Danube, the Lech and the Alps; but its complete settlement was a work of time.
The Bavarians soon came under the dominion of the Franks, probably without a serious struggle; and were ruled from 555 to 788 by dukes of the Agilolfing family, who were possibly of Frankish descent. For a century and a half a succession of dukes resisted the inroads of the Slavs on their eastern frontier, and by the time of Duke Theodo I., who died in 717, were completely independent of the feeble Frankish kings. When Charles Martel became the virtual ruler of the Frankish realm he brought the Bavarians into strict dependence, and deposed two dukes successively for contumacy. Pippin the Short was equally successful in maintaining his authority, and several marriages took place between the family to which he belonged and the Agilolfings, who were united in a similar manner with the kings of the Lombards. The ease with which various risings were suppressed by the Franks gives colour to the supposition that they were rather the outcome of family quarrels than the revolt of an oppressed people. Between the years 739 and 748 the Bavarian law was committed to writing and supplementary clauses were afterwards added, all of which bear evident traces of Frankish influence. Thus, while the dukedom belongs to the Agilolfing family, the duke must be chosen by the people and his election confirmed by the Frankish king, to whom he owes fealty. He has a fivefold wergild, summons the nobles and clergy for purposes of deliberation, calls out the host, administers justice and regulates finance. There are five noble families, possibly representing a former division of the people, after whom come the freeborn, and then the freedmen. The country is divided into _gaus_ or counties, under their counts, who are assisted by judges responsible for declaring the law.