Gallic tribal rivalries made the Romans' job very much easier. And when at last they were able to unite under Vercingétorix in 52 BC, the occasion was their total and final defeat by Julius Cæsar at the battle of Alésia.

This event was one of the major turning points in the history of France. Roman victory fixed the frontier between Gaul and the Germanic peoples at the Rhine. It saved Gaul from disintegrating because of internal dissension and made it a Roman province. During the five centuries of peace that followed, the Gauls farmed, manufactured and traded, became urbanized and educated - and learnt Latin. Roman victory at Alésia laid the foundations of modern French culture and established them firmly enough to survive the centuries of chaos and destruction that followed the collapse of Roman power.

Augustus and Claudius were the emperors who set the process of Romanization going. Lugdunum (Lyon) was founded as the capital of Roman Gaul as early as 43 BC. Augustus founded numerous other cities - such as Autun, Limoges and Bayeux - built roads, settled Roman colonists on the land and reorganized the entire administration. Gauls were incorporated into the Roman army and given citizenship; Claudius made it possible for them to hold high office and become members of the Roman Senate, blurring the distinction and resentment between colonizer and colonized. Vespasian secured the frontiers beyond the Rhine, thus ensuring a couple of hundred years of peace and economic expansion.

Serious disruptions of the Pax Romana only began in the third century AD. Oppressive aristocratic rule and an economic crisis turned the destitute peasantry into gangs of marauding brigands - precursors of the medieval jacquerie . But most devastating of all, there began a series of incursions across the Rhine frontier by various restless Germanic tribes ; first came the Alemanni, who pushed down as far as Spain, ravaging farmland and destroying towns.

In the fourth century the reforms of the emperor Diocletian secured some decades of respite from both internal and external pressures. Towns were rebuilt and fortified, an interesting development that foreshadowed feudalism and the independent power of the nobles since, due to the uncertainty of the times, big landed estates or villae tended to become more and more self-sufficient - economically, administratively and militarily.

By the fifth century, however, the Germanic invaders were back: Alans, Vandals and Suevi , with Franks and Burgundians in their wake. While the Roman administration assimilated them as far as possible, granting them land in return for military duties, they gradually achieved independence from the empire. Many Gauls, by now thoroughly Latinized, entered the service of the Burgundian court of Lyon or of the Visigoth kings of Toulouse as skilled administrators and advisers.