Bavarii was a large and powerful tribe which emerged late in Teutonic tribal times, in what is now the Czech Republic (Bohemia). They replaced, or perhaps are simply another phase of, the previous inhabitants - the Rugians. They swiftly expanded their influence southward, and occupied Austria and the area which still bears their name: Bavaria. There is some argument as to the origins of the Bavarii. Until recently, modern day Bavarians were thought to be descendants of the Bavarii, who themselves were direct descendants of the (most probably) Celtic Boii, who settled in what is now Bavaria perhaps as much as two centuries before the birth of Christ. The Boii may in turn have also lent their name to Bohemia, an area that has at times been part of Bavaria proper.

Over the last half of the 20th century, historical and archaeological research has increasingly supported the theory that the remnants of the Celtic Boii were absorbed into the Roman Empire and later intermingled with other Germanic peoples who chose to stay (or were stationed by the Romans) in the area. By the 6th c. AD we see evidence of the foundation of a Bavarian Stem-duchy whose leading men were related to the ruling Frankish (and possibly Alemannic/Swabian) houses. However, there is no longer real evidence that the rulers in Bavaria belonged to a people called the Bavarii. It is in fact likely that, after the name of the region became known by the name of the early inhabitants, later inhabitants became known by the accepted geographical name.

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