Douglas Harper's Etymology Dictionary
Gallo-Roman
"belonging to Gaul when it was part of the Roman Empire," from comb. form of Gaul + Roman. In reference to a language, and as a noun, the language spoken in France from the end of the fifth century C.E. to the middle of the ninth, a form of Vulgar Latin with local modifications and additions from Gaulish that then, in the region around Paris, developed into what linguists call Old French.
Wikipedia
Gallo-roman
Usage examples of "gallo-roman".
An old abbey on the site of Gallo-Roman thermae, and she would walk into the court-yard described and up into the half-round hall where you can sit on the shallow well of steps and look at the six tapestries.