The 2019 fire at Notre-Dame de Paris has revealed yet another of the cathedral's secrets: the 12th-century Gothic-style building is the first such structure known to be constructed with an iron skeleton.
The blaze devastated the iconic cathedral, which is still undergoing repairs almost four years later. Still, among the scorched ruins, a number of incredible finds have emerged, including two lead sarcophagi that have since been opened. Now, the fire has allowed archaeologists to access and analyze the iron staples used to bind stones together during the building's construction.
The technique has never before been documented in architecture of this time period, making Notre-Dame, built in the 1160s, the first building of its type to be bolstered by iron staples throughout its structure and something of a marvel of medieval innovation.
This, the authors of a new study on the finding say, could help explain the cathedral’s extraordinary height: with a nave reaching 35 meters (115 feet) and two 69-meter (226-foot) towers, it was the tallest building ever erected at the time of its construction.
"When we studied other Gothic churches of that time period, none used iron in their construction," lead author Maxime L'Héritier told Live Science. "We believe that the staples were what enabled them to build this structure at such a terrific height."
L’Héritier and colleagues sampled 12 iron staples from different locations in the cathedral, including the tribunes, nave aisles, and upper walls, and were able to date six of them using a type of radiocarbon dating. The staples, which measured up to 50 centimeters (20 inches) in length, were used in the earliest phases of construction, the team found, placing them in the mid-12th century.
“Radiocarbon dating reveals that Notre-Dame de Paris is indisputably the first Gothic cathedral where iron was thought of as a real building material to create a new form of architecture,” the authors said in a statement. “The medieval builders used several thousand of iron staples throughout its construction.”
As well as highlighting architectural innovation, the study sheds some light on the iron market in 12th and 13th century Paris, although further analysis of the samples is needed before those secrets are to be fully revealed.
The study is published in PLOS ONE.