If there is a subject for the Blue Flower, it is that of the great Romantic French architect Eugène Emmanuel Viollet-le-Duc (1814 – 1879). I encourage you to watch this video, which is in French:
Gothic restorations of the nineteenth century might have lacked complete academic authenticity, but Viollet le Duc was a major influence in the Gothic Revival like Pugin in England. Without his work, many great French churches would have crumbled and collapsed after the abuse meted out by the revolutionaries and the merciless weather.
Again, a blessing in disguise, the fire of Notre-Dame de Paris has brought the patrimony of the Middle-Ages and the Gothic Revival into the foreground. Now is the time to appreciate our churches and cathedrals and remember why they were built – man’s homage to the glory of God. Viollet le Duc’s work is a part of this patrimony to treasure, restore and appreciate.
The Blue Flower 
Thank you for this! One of the many things I was wondering about, in my imperfect memory of whatever I once knew about Notre Dame, was the extent of Viollet le Duc’s work, there.