The 2019 Notre-Dame Fire Revealed Iron Staples Holding the Cathedral Together

The 2019 fire in Paris’ Notre-Dame Cathedral destroyed the Gothic structure’s wooden roof and toppled its iconic spire. But the disaster comes with a small silver lining: Due to the fire—and the ongoing restoration process—researchers are getting an unprecedented look at the cathedral’s inner workings.

According to a paper published in the journal PLOS One this week, large iron staples have been found holding together the cathedral’s stone blocks. In light of this unexpected discovery, scientists say that Notre-Dame is the first known Gothic cathedral to make such extensive use of iron as a construction material.

Crews began work on the cathedral in 1163 and finished in 1345. Researchers now know that they used hefty iron staples—measuring nearly 20 inches long and weighing between 3 and 9 pounds—to reinforce the stone blocks that make up the cathedral’s walls, nave aisles and tribunes. Prior to the fire, the staples supported load-bearing areas of the cathedral, “indicating the iron crucially improved the cathedral’s structural integrity,” as Gizmodo’s Isaac Schultz writes.

Iron also served an aesthetic purpose: The staples allowed medieval builders to construct a large, sturdy structure that appears to be slender and delicate.

“Compared to other cathedrals, such as Reims, the structure of Notre-Dame in Paris is light and elegant,” says Jennifer Feltman, an art historian at the University of Alabama who was not involved in the research, to New Scientist’s Jeremy Hsu.

Builders in France installed iron reinforcements in other medieval cathedrals, including those in Beauvais, Chartres and Bourges. Those structures, however, were built after Notre-Dame.

Researchers analyzed 12 of the cathedral’s historic staples. Using radiocarbon dating, they learned that they were made during the early phases of construction, around the year 1160. They also hope to discover where the iron came from.

“We’re trying to figure out if it’s local or more distant,” says lead author Maxime L’Héritier, a historian at Paris 8 University, to Live Science’s Jennifer Nalewicki. “There also seems to be different ore sources depending on whether the construction occurred in the 12th or 13th centuries. We do know that the [cathedral’s] bishop died at the end of the 12th century, so it’s possible that a new ore resource was used years later. We should know more in a year or two.”

In addition to the iron staples, restoration work has uncovered some other surprising secrets: Last spring, archaeologists found two lead sarcophagi buried underneath Notre-Dame’s floor. In December, they announced that they’d identified one set of remains as Antoine de la Porte, a high priest who died in 1710. The other coffin held the skeleton of an unidentified man, likely a horseback rider, from an earlier period.

More discoveries may be to come. Scientists remain hard at work investigating and repairing the cathedral, which is slated to reopen in December 2024. 

For many of the experts involved, including L’Héritier, the process of carefully repairing one of the world’s most celebrated buildings can be emotional. The first time he saw the destruction up close, L’Héritier was “speechless,” he wrote in a 2021 essay for the anthropology magazine Sapiens.

“The atmosphere was oppressive,” he added. “Although I had watched the fire many times on television, only at that moment did I truly realize how devastating the blaze was and how demanding the task was before us.”

Sarah Kuta | READ MORE

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.