The tragedy that struck one of the world’s most recognizable and beloved landmarks offers France a chance to heal after months of civil unrest. As with any unfortunate event, sympathy from a horrified world will be followed by prognostications over issues surrounding the fire and its aftermath. Foremost among these will be approaches to restoring the missing historic elements that now lie in rubble on the floor of the cathedral.

I have spent my professional life working in building conservation and architectural history, with particular expertise in historic religious buildings. Like many churches, Notre-Dame has seen its congregation change during the past 50 years and has faced fundraising challenges in procuring necessary funds for maintenance and restoration. The fire that nearly destroyed the church was most likely caused by construction activity near Eugène Viollet-le-Duc’s cast-iron spire at the center of the transept. The irony of this will not be lost on those familiar with medieval restoration, or with 19th century construction.

Viollet-le-Duc (1814–1879) invented modern restoration—both theory and practice. His first laboratory was Notre-Dame de Paris, and he spent virtually his entire professional life studying the cathedral and restoring it. Indeed, everything he added, subtracted, or restored is documented in extensive records and writings. Nothing he built at Notre-Dame was as controversial, or as beloved, as the 180-foot spire that fell last Monday. The cathedral had no spire when he began work in 1844 (the previous one had been removed in 1786). It also had no lead gutters and leaders, no gargoyle scuppers, and no metal transept statues. These modern improvements were entirely conceived and designed by France’s 19th century restoration genius.

Viollet-le-Duc has both champions and detractors in the French conservation community. Among architects, his name is often associated with both “rationalism” and “historicism,” contrasting ideals in modern architecture. There should be no doubt about French ambivalence toward the eventual restoration of not only his spire, but also roof construction above the historic timber rafters that burned last week. Still, the abrupt announcement of an architectural competition for designs to replace the spire was a surprise to many who see the existing fabric as sacrosanct. Like President Emmanuel Macron’s hasty promise to restore the building in five years, the announcement does not bode well for a satisfactory restoration effort.

French architects are among the most technology-obsessed designers in the world, and therefore are not likely to favor by-the-book restoration of all historic materials and elements. Paradoxically, France also has some of the best government restoration organizations, and many of the finest building craftsmen in Europe. Many restoration specialists are trained by Les Compagnons du Devoir, a trade and education organization founded by Pierre de Coubertin at the beginning of the 20th century. Hand skills and artisanal knowledge are highly valued.

These facts make conflicts between government, the architectural profession, and the restoration trade community inevitable. Observers from countries like England and Germany are already offering advice on how to address some of the contentious issues, but there is no culture quite like French culture when it comes to parochial things like heritage. Preserving la grande patrimoine is a sacred cause, but one that Parisians argue about incessantly. The nation will not rally behind a straightforward restoration program, as England did after fires at Hampton Court and Windsor Castle. With contributions coming from the fashion industry, any solution will have to be à la mode.

Still, there is a historical imperative at work that favors the retention of elements that are essential to the history of modern restoration, as practiced by its most influential architect. Viollet-le-Duc’s work at Notre-Dame is as significant in its own right as anything built there during the 12th and 13th centuries. Hearing the mayor of Paris talk of a new spire is deeply troubling to all who understand this fact. Even more troubling are articles by ill-informed critics such as Aaron Betsky, who argue for a rethink of the entire building. As a UNESCO heritage site, the cathedral of Notre-Dame must be treated not only as a Parisian landmark, but also as a cultural monument treasured throughout the world. That is one of the reasons why any restoration plans must be vetted with international as well as national authorities.

A second, and equally important, question facing those charged with rebuilding the cathedral is how to restore the wooden roof structure. I have dealt with this issue repeatedly, and it is by no means straightforward. The massive “trees” that supported the lead roof were more than 800 years old and cannot be replaced in kind. They were never visible to the public, but were nevertheless “present” in the historical imagination, owing to books like Victor Hugo’s Hunchback of Notre Dame. Without fire partitions and sprinklers, they provided fuel for the massive blaze that nearly toppled the entire building. Engineers with safety in mind will demand a fire-resistant structural system for the restoration.

Viollet-le-Duc would be on their side, as he wrote favorably about improving the technology in historic buildings when better materials or systems are available. The issue of gutters was one he addressed in Volume 8 of the Dictionnaire raisonné. Arguing that they should be installed on all Gothic and Romanesque churches, he insisted that master masons would have used them had the option presented itself.

A careful assessment of the roof structure and metal roofing layers will undoubtedly raise many questions. Though I am not familiar with the precise configuration at Notre-Dame, I suspect that Viollet-le-Duc had his hand in some improvements to the roof structure in the mid-19th century. These should be taken into consideration in any plans to rebuild the roof. Of course fireproofed steel-and-concrete systems will be considered, though the weight of any structure must be a primary criterion, as thin limestone walls, even with buttresses, will not support heavy trusses. One system should be immediately off the table: a “Reichstag” solution using glass roofs and space frames. (Norman Foster should stay in London and mind his own business.)

I doubt that the French will replace the wooden roof in kind, but I remain concerned about any unproven, high-tech structural systems that may not protect the delicate rib vaults in the ceilings below. Engineer Robert Mark, of Princeton, did much of the best thermoplastic modeling and testing of such vaults decades ago. His discoveries should help to guide the restorers.

The thin stone vaulting is a primary concern in the near term, as mortar can leach from the joints during and after rainstorms. One of the things that may forestall a quick restoration is the need for testing and careful restoration of the vaults and walls prior to the rebuilding of the roof above. Walls near the towers and the transept have already been reinforced to prevent buckling. Five years is a rather short period when one considers these complexities.

The spirit of Viollet-le-Duc hovers above the finials and buttresses of Notre Dame, today more than ever. His far-reaching interventions in the fabric of the building began modern restoration and will no doubt color all subsequent building campaigns in this jewel of Gothic architecture. He returned the facade to its former glory after revolutionary zealots had cut heads off statues, reinforced the structure where needed, removed 18th century interiors, and designed a splendid rectory. Let us hope that French authorities recognize his importance as they consider replacing any elements lost in the fire, especially la flèche at the apex of the crossing. Any less would be an affront to their nation—and to the world.

Featured image of Eugène Emmanuel Viollet-le-Duc by Nadar, via Wikipedia Commons.