Notre-Dame 'indisputably' first of its kind to use iron reinforcements

Researchers have determined that the Notre-Dame de Paris is "indisputably" the earliest known cathedral of Gothic-style architecture to have been initially constructed using substantial usage of iron to bind stones together, according to a study published in PLOS ONE on March 15.

The analysis could also deepen understanding of the iron trade, circulation, and forging in 12th and 13th century Paris. 

The great fire of Notre-Dame reveals iron

At a height of 32 meters when it was built in the middle of the 12th century, Notre-Dame was the tallest structure ever constructed. According to earlier studies, this record may have been made feasible by integrating several architectural advances.

However, despite the widespread usage of iron reinforcements in more recent cathedrals and efforts to restore historic structures, it remained unknown what function iron may have served in Notre-initial Dame's construction- until now. 

Maxime L'Héritier of Université Paris 8, France, and colleagues could access previously concealed parts of Notre-Dame that hold clues to the possible use of iron in its construction due to the 2019 fire and subsequent restoration. 

The researchers collected material samples from 12 iron staples used in the tribunes, nave aisles, and upper walls of the building to hold stones together. They used microscopic, chemical, and architectural investigations along with radiocarbon dating to learn more about the staples.

The team's research indicated that during the construction of Notre-Dame in the 1160s, iron staples were undoubtedly utilized throughout the building process, making it the first building of its kind to do so.

"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 press release. 

"The medieval builders used several thousand of iron staples throughout its construction," they added. 

The analyses also offer details that may increase understanding of the iron trade, circulation, and forging in 12th and 13th century Paris when combined with other archaeological and historical facts from that period.

For instance, the authors highlighted that several staples appear to have been created by "welding together" pieces of iron from various supply sources.

Is Notre-Dame still being restored?

They state that additional analyses of Notre-Dame materials and a thorough database of historical iron producers in the area are required to corroborate and build on these novel discoveries regarding the medieval Parisian iron market.

Nearly four years have passed since a fire ripped through Notre-Dame cathedral in Paris on April 15, 2019. The 12th-century landmark is currently undergoing reconstruction, with plans to reopen to both visitors and churchgoers in December 2024, according to French officials.