It is with the Romans that we get our first recorded history of France, known to the Romans as Gaul. It is Julius Caesar himself who provides the account of the conquest of Gaul in his book, The Gallic War. Roman France lasted from roughly 125 BC to 486 AD. An enormous span of time, during which the previous Celtic culture transformed, and becomes known as Gallo-Roman culture.
So what did the Romans do for France? Their own answer would have been quite simply that they brought 'civilisation'. They viewed the Gallic Celts they encountered as mere barbarians. It is true that the Romans brought a common European language, Latin, a road infra-structure which linked France to the rest of the Roman Empire, villas with underfloor and inside wall heating, baths, private and public, and the concept of a 'modern' urban environment, besides much else from law to water supplies. Yet the Celts themselves were not the raw savages the Romans portrayed having their own fortified 'towns', and great skills in craft work of all types, from ironwork to leatherwork.
There was, of course, war too, both the original conquest, revolts, and finally the defeat of the Romans by the Germanic Franks in the 5th century; yet the mark of Rome remained to touch many aspects of French life, not least the introduction of Christianity in the first century AD. The Romans left many marks of their rule including some magnificent pieces of architecture, such as the great amphitheatre in Arles, still used for performances today.
Having said all of this, many historians would begin their history of France after the Romans had left. In my view this leaves an incomplete national story - but the final choice is, as always, yours to make!
Books to add to the previous list on my blog-:
The Identity of France, Vols 1 and 2 by Fernand Braudel ( Two impressive volumes from a great French historian)
The Celts by Simon Jenkins (a great introduction)
Blood of the Celts by Jean Manco (looking at modern DNA evidence)
The Conquest of Gaul by Julius Caesar
Roman Gaul in the Charles Rivers Series