Everyone says that Romance languages overtook the Celtic languages in places like Spain and Gaul, but nobody explains how exactly this happens. Wouldn't Latin speaking immigrants have to outnumber the natives to replace the language? Certainly just being ruled by Rome isn't enough to have your language replaced, since Common Brittonic wasn't replaced by Latin. It seems insane to me that an entire language group from a country the size of France can simply disappear because of foreign occupation.