The titanic construction site of Notre-Dame de Paris has allowed us to better understand the cathedral, its construction and its history. Since the fire of 2019, around a hundred scientists have looked into the previously little-studied monument, in particular because of its high attendance.
How was this scientific project born?
Immediately after the disaster, specialists and researchers “volunteered to help with the restoration”, recalls Philippe Dillmann, research director at the CNRS and one of the coordinators of the CNRS/Ministry of Culture scientific project. Their expertise was used, for example, to “analysis of materials, their resistance, assistance with structural calculations for architectural design offices…” Several also proposed to work on “historical aspects, construction, metal, glass, stone, wood, sound environment…”
What did the study of wood show?
The examination of the calcined beams of the framework made it possible to better understand in particular “the way it was made”. Carpenters did not use “not wood dried for many years, but green wood”. Oaks “around a hundred years old, around fifteen meters slender, cut with a doloire (a sort of axe) respecting the fiber to maintain its resistance. All this was used for the restoration.”
Analysis of certain wood elements “indicated the nature of the soil on which the tree had grown, particularly in the Ile-de-France forests.” Researchers have also discovered on remains “rope holes used to bind logs, like rafts, for transport by the Seine”. The study of wood also provided data on the medieval climate: “The tree absorbed oxygen from the atmosphere during its growth and we can derive information from it on the temperatures at the time in the Paris region. This confirmed the small warming experienced in the Middle Ages, without any comparison with that which we are experiencing today.
How was metal used?
It was one of the important discoveries of the scientific project: in the 19th century, the architect Eugène Viollet-le-Duc had “revealed some iron staples binding stones together, but we didn't think there would be so many”, underlines Philippe Dillmann. Many were discovered at the top of the walls, under the burned framework. “They play a fairly obvious role as a belt on the building. But we found others on the columns of the choir, on the walls of the stands on the 1st floor… Their role sometimes raises questions and continues to be studied. »
Several staples, 25 to 50 cm in length, were analyzed and radiocarbon dating was carried out. The results indicate that “the oldest date from the 1160s, that is to say at the beginning of the construction of Notre-Dame. It is now undoubtedly the first Gothic cathedral where iron was thought of as a real building material to create unique architecture. This innovation then spread to other buildings such as Chartres, Bourges or Beauvais. »
What did examining the stones teach scientists?
The study of the stones, all extracted from limestone rocks of the Paris basin, has “permitted to collect a lot of information on the construction of Notre-Dame”, notes the scientific coordinator again. A surprise was to note the “thin thickness of the vaults (15 to 18 cm in the choir and around 20 cm in the nave), which nevertheless played the role of fire protection”. The tool marks left on the stones also provide information “on pruning techniques”.
What information was discovered about construction methods?
Dating of wood and staples “more precisely documents the construction phases”. The researchers were also able to observe a “reuse of materials in several places. The dating of the wood showed, for example, that the second framework of the choir, built in the 13th century, when the cathedral was enhanced, was made with elements of the first dating from the 12th.”
Analysis of the marks left by stonecutters on their work “made it possible to understand that teams of craftsmen worked independently to the north and south of the nave”. The scientists were also able to observe, for the first time, the foundations of the cathedral and in particular those of the pillars, connected together by stringers, beams used to distribute the load.
Were there any other significant discoveries?
Yes, particularly during archaeological excavations, which revealed a lead sarcophagus which could be that of the poet Joachim du Bellay and the remains of the old rood screen (monumental stone fence closing the choir, dating from the 13th century and destroyed in the 18th century). . The complete examination of the monument has also “allowed us to document certain knowledge: to authenticate, for example, the medieval elements of the stained glass windows, the only ones being on the large rose windows of the transept”, note Philippe Dillmann. “A group of researchers also continues to work on acoustics, another on heritage emotion to understand how this fire marked the populations and how they mobilized…” All of the work made it possible to “collect a lot of recorded data which remains to be studied”. All of them are moreover “stored in a digital twin of the cathedral. This virtual double will be made available to the teams.”
