Scientists hoped, but did not dare to express the wish too clearly. What if the fire that had ravaged Notre-Dame de Paris Cathedral on the night of April 15, 2019, shocking the international community, offered a unique opportunity to revisit the history of French religious construction? The absence of the public inside the structure for a number of years would give them the opportunity for in-depth studies. Above all, the disappearance of the framework and the collapse of the spire and part of the vaults would reveal the building’s secrets to researchers’ eyes and analysis.
And now it’s done. After the discovery by archaeologists of two tombs and numerous pieces of the ancient rood screen buried under the transept crossing, a team of historians, chemists and metallurgists announced in the March 15 issue of the journal PLOS One that the cathedral could well be “the first iron lady.” “While other churches, such as those at Laon [Aisne, in northern France] and Noyon [Oise, north of Paris] were reported to have made use of iron, Notre-Dame presents a truly systemic use of metal throughout its construction,” announced Maxime L’Héritier, lecturer in medieval history at the University of Paris-VIII Vincennes-Saint-Denis and lead author of the article.
‘Thousands of Staples’
In the first detailed observations after the fire, L’Héritier and his colleagues discovered metal staples in the rubble of the cathedral. With a melting temperature of 1,500°C, the iron had easily withstood the 800°C of the inferno. As the months went by, hundreds of them were found at different levels of the building. “If we extrapolate to the parts that remained inaccessible, thousands of staples were used by the builders,” L’Héritier observed.
“Bourges, Beauvais and Tours also show extensive use of metal reinforcements, but that’s several decades later and with a different technique” – Maxime L’Héritier, historian
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It is necessary to specify here what we are talking about. Apart from their shape, these staples have nothing to do with the small pieces of silvery metal that clip our stacks of paper together. Between 20 cm and 98 cm long, and weighing up to 4 kg, these pieces, sealed with lead, make it possible to fix blocks of stone at difficult points. These reinforcements can be found in the lower part of the cathedral, under the arches of the galleries, above the ambulatory, and on the top, on the side walls, where the framework rested.
So when were these staples installed? “Had they been added during one of the renovations that the building has undergone, or from its conception?” asked Philippe Dillmann, head of LAPA at the University of Paris-Saclay and coordinator of this research. The dating of six staples, 40 to 50 cm long, by the Carbon 14 Measurement Laboratory (LMC 14) in Saclay, was decisive. The researchers concluded that the two pieces from the galleries are “no later than 1160.” In other words, they were installed during the construction of the galleries, at the start of work at the site. As for the four pieces from the upper walls, the analysis concludes that they were made between 1200 and 1220. “This corresponds perfectly with the new dating of the framework, namely 1215,” L’Héritier happily reported.
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