Where did the Gauls come from before France?

Gaul was not a people but a territory (modern France, Belgium, the south Netherlands, western parts of Germany and northern Italy). It was inhabited by the Celts in the Iron Age. About 900BC, tribes of Celts advanced even westward. Britain also was inhabited by the Celts before the Roman rule. The area north of the Alps was occupied by the Romans (Julius Caesar - 58-51 BC - was called Transalpine Gaul, and remained under Roman rule until the 5th century AD. The territory of modern France was garadually invaded by the Goths, Franks and Burgundians after 330.ce today.