Scientists working on the scorched interior of Notre-Dame de Paris have found iron was used in the cathedral’s construction in the mid-12th century. It’s an unexpected discovery that changes how researchers thought the church was built, and provides surprising insights on the iron trade in 12th-century Paris.

The findings were made possible—ironically—by the devastating fire that swept through the famous cathedral in April 2019 during planned renovations. The fire destroyed most of the church’s roof and prompted unprecedented repair work on the building, which is expected to reopen in 2024. Groundbreaking on Notre-Dame de Paris began in 1163, and construction was completed in 1345.

The process of restoring the cathedral to its former glory has opened up opportunities to study aspects of the church’s construction that had been overlooked or impossible to analyze when the building was intact.

Most recently, a team of archaeologists and conservationists found and dated iron staples found in the cathedral’s tribunes, nave aisles and upper walls. The team’s research was published today in PLoS One.

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