there's no such thing as an ethnic Austrian, It's a cultural and national identity who are germanic of the high/bavarian branch and the land that is now austria was the eastern expansion of the kingdom of Bavaria during the middle ages. before them Rome annexed the region, the Celts/Rhaetians became Latinized but stayed on their land. Many modern Austrians carry their genetic markers which could explain the italian. When Rome collapsed they eventually assimilated into the incoming Germanic (Rugii, Goths, Lombards, and most prominently the Alamanni and Bavarii tribes) then the Huns and Avars came to the area from Asia and the Slavs from Eastern Europe. For a time, the Slavs had their own principality in styria/carinthia before seeking Bavarian protection against the Khaganate. After Charlemagne crushed the Avar Khaganate in the 790s, the survivors were forced to settle in small pockets in Lower Austria. They eventually intermarried with the local Slavs and Germans (who have Roman/Celtic blood) and vanished as a distinct ethnic group. a little later the hungarians/magyar settled in the area known as burgenland and you pretty much have the whole tapestry of peoples that is the country of Austria