According to Roman texts, the Celtic settlement at Passau was known as “Boiodurum”, a combination of the name “Boios” and the suffix “durum”. “Durum” is related to the Irish word “Dor” or “Tor” and refers to a large, fortified settlement. Archaeological evidence for Celtic occupation was found on the plateau of the Domberg. Around 400 BC, the inhabitants of Boiodurum erected a fortification here. This took the form of a box construction of timber and packed earth. A short time later, the complex burned down, perhaps as the result of an enemy assault, but it was immediately rebuilt. At present it is not clear whether these ramparts once protected a larger settlement or the seat of a Celtic prince – more excavations are needed to be able to answer this question. Salt is likely to have been one of the main goods traded in Boiodurum. At the time, this valuable commodity was mined at the Dürnberg, close to Hallein in Austria. From there it was transported to Passau along the rivers Inn and Salzach.