The “Dictionnaire raisonné de l’architecture française du XIe au XVIe siècle” is an overwhelming reference work consisting of 9 books (some 5,000 pages in total) on medieval and renaissance architecture in France. It is written in French, as you already suspected, but the detailed illustrations make it worthwhile for all architecture and history devotees. There is really all you need to know to build, for instance, a gothic cathedral, including the gargoyles. The work appeared in 1856 and was written by Eugène Viollet-le-Duc, an architect known for his restorations of medieval buildings. The separate volumes can also be found on the Internet Archive.