Before the Roman conquest, the indigenous Celtic tribe of the Raurici were settled in the Basle region. One of their settlements was located on the Münsterhügel hill in Basle. In 58 BC the Raurici, together with other Celtic tribes including the Helvetii, migrated west with the intention of settling in the Bordeaux region in France. This ’Helvetian exodus’ came to an abrupt halt near Bibracte (France) where Roman troops led by Julius Caesar, who was on a mission to conquer Gaul at the time, defeated the Celtic emigrants. The vanquished Celts were forced to return to their homelands.

Eventually, all the regions west of the River Rhine fell under Roman sovereignty. Around 44 BC, Lucius Munatius Plancus, the governor of Gaul, founded a colony town in the territory of the Raurici. The colonial lands, i.e. the Colonia Raurica, located right on the border of the empire, were intended as a buffer zone to protect the region from Germanic incursions and to control the trade and transport routes. Celtic coins continued to be used for a long time as a means of payment in the Roman town of Augusta Raurica.