I see only one response among the ones here about the Romans. The Roman sites I visited when I was serving in Germany were quite well-done for documentation and I expect the ones in France would be the same. The recommendations you’ve received are all great on the more recent sites but I wouldn’t want you to overlook a Roman site by running out of time.
>>I see only one response among the ones here about the Romans<<
Roman sites can be fantastic! But I have the impression that the really impressive Roman sites in France are mostly in the southern part of the country.
And I second all the recommendations about Normandy.