The Germanic Alamans started invading the Swiss Plateau in the 3rd century from north of the Rhine, despite the line of Roman fortifications. From the 4th century onwards, the Germanic peoples of northern and eastern Europe were on the move, pushed westward by Huns and other tribes migrating from Central Asia.

The Roman legions finally withdrew south of the Alps at the beginning of the 5th century as Rome itself came under threat from migrating tribes, leaving their former provinces to fend for themselves.