An interesting alternative history scenario (which could potentially have made a vast difference in the modern age) would be if the Gauls had decided to occupy or destroy the Romans rather than exact tribute following the
Battle of Allia. This would be entirely possible and is not a far fetched change from reality. Though a Celtic Europe was seemingly already being influenced by Mediterranean cultures via Greek merchants, the tradition of law and various other aspects of the Western world might be completely different. And who knows if the Germanic invasions would ever have occurred on the scale they did without the incentive of pilfering, or becoming by citizenship, one of the Romans.