The French language through the ages

French is the language of French-speaking Switzerland. It sounds obvious. And yet, it hasnʹt always been so. For a long time, patois was spoken. A different dialect in each region, but with a common root, Franco-Provencal, with the exception of the present-day canton of Jura, whose origin is the language of dʹoïl. How has the language evolved in Western Switzerland since prehistoric times?