Scientists working on the burnt interior of Notre Dame de Paris discovered that iron was used in the cathedral’s construction in the mid-12th century. It’s an unexpected discovery that changes the way researchers think the church was built and provides surprising insights into the iron trade in 12th-century Paris.
The findings were made possible – ironically – by the devastating fire that engulfed the famous cathedral in April 2019 during planned renovations. The fire destroyed most of the church’s roof and prompted unprecedented renovations to the building, which is expected to reopen in 2024. The first sod of Notre Dame de Paris began in 1163 and construction was completed in 1345.
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The process of restoring the cathedral to its former glory has opened up opportunities to study aspects of the church’s construction that were overlooked or impossible to analyze when the building was intact.
More recently, a team of archaeologists and conservationists discovered and dated iron brackets found in the cathedral’s stands, naves and upper walls. The team’s research was published today in PLoS One.
“The fire shed light on certain uses of iron, such as the brackets at the top of the upper walls, which were completely hidden by the frame,” said Maxime L’Heritier, an archaeologist at the National Center for Scientific Research and the study’s lead author, in an email to Gizmodo. “We wouldn’t be able to see them without the flame or a huge restoration.”
Iron brackets at the top of one of the walls of Notre Dame.
French authorities said the fire that broke out at Notre Dame on April 15, 2019, was likely caused by an electrical fault or a burning cigarette. Over the course of 15 hours, the fire toppled Notre Dame’s iconic spire and destroyed “la forêt” (literally “the forest”) of felled oak trees that made up the church’s rafters. The roof, spire and other components of the church are made of lead, which spews toxic waste over Paris as Notre Dame burns.
L’Héritier added that other medieval French cathedrals – at Bourges, Chartres, Reims and Beauvais – all used iron fittings as well as iron bars and chains. But these structures were built later than Notre Dame, showing that the consecrated cathedral of Paris set the scene for what came next, from its scale to its brackets.
“We used to believe that these great builders’ yards of the 13th century invented these building processes using iron fittings, but now it seems that it all happened at Notre Dame,” said L’Héritier.
The brackets were placed at certain points in Notre Dame’s architecture that the researchers believe are load-bearing (or would have been before the fire), indicating that the iron greatly improved the cathedral’s structural integrity. The brackets stretched over stones, binding the walls together.
Iron, L’Héritier said, made possible the construction of Notre Dame’s “slender Gothic architecture,” including its iconic flying buttresses and slender arches, aspects of the building that make it appear elegant despite its enormous scale.
Although the major discovery was unexpected, it was not the first surprise to emerge from Notre Dame’s restoration. In March 2022, archaeologists announced that workers assessing the stability of the cathedral’s floor had discovered two lead sarcophagi among the post-Napoleonic plumbing. Later in the year, one set of remains was identified as Antoine de la Porte, an ecclesiastical authority with “exceedingly good teeth” who died in 1710. (The identification was not difficult – de la Porte had a plaque on his coffin. )
The other remains date from the 14th century and have not been identified, but the individual had a deformed head, wore a wreath of flowers and was likely a rider based on the condition of the skeleton’s hips, according to the Guardian.
Reopening in 2024 should be viewed like missile launches; that is, it can be pressed at any time. Renovating a UNESCO World Heritage site is not something to be rushed, especially after an inferno that raises questions about the building’s structural integrity.
But what was undeniably a horrific event has a silver lining: Because of the fire, researchers are able to interrogate parts of a historic structure that they otherwise wouldn’t. Notre-Dame de Paris has centuries of secrets hidden within its walls, and now is science’s chance to unearth them.
More: Rare Roman statues found under medieval church in England
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