The Notre Dame cathedral fire revealed a long-hidden secret for the famous Parisian monument

Notre-Dame was the first Gothic cathedral whose construction made extensive use of iron staples. This was a long-kept secret about the famous Parisian landmark before it was engulfed by fire four years ago. The iron reinforcements were found by a team of archaeologists after an extensive restoration effort that is still ongoing.

A study that was released in the journal PLOS ONE on Wednesday claims that it was the tallest building of its period, with vaults that could go as high as 105 feet. The research comes to the conclusion that Notre-Dame is unquestionably the first known Gothic cathedral where iron was extensively used to bind stones as a proper construction material.

The lead author of the research and University Paris 8 archaeologist, Maxime L'Heritier, said that some aspects of the building's construction are still unknown even after all these years. How the builders "dared — and succeeded — in putting up such thin walls to such a height," he said, was unclear. Since there isn't much evidence from more than 900 years ago, "only the monument can speak," he continued. It should be outlined that the famous cathedral in the center of the French capital was not finished until nearly a century after building had started in 1160.

According to L'Heritier, this is the first significant use of iron in a Gothic cathedral, in very specific places. Since Antiquity, iron staples have been used in building, and examples include the Colosseum in Rome and Greek temples. However, in those monuments, they were merely used to maintain the stability of big stone blocks on the lower floors.

The fire on April 15, 2019, revealed iron staples that were used to join the stone blocks of the church. Some dropped to the ground smoldering in the heat of the fire while others appeared in the building's frame. According to the research, the cathedral may contain over a thousand iron staples. The staples come in a variety of sizes, weighing up to a few kilograms and spanning in length from 10 to 20 inches. They were discovered throughout the church, including in the choir tribunes, the cornice, and the walls of the nave.

Beginning in the early 1160s, the cathedral's supports were constructed using iron staples. Over the following 50 to 60 years, their successors maintained their creative use on the upper parts of the walls. This use of iron would continue in a number of cathedrals throughout France. Archaeologists have also discovered a number of tombs at the church, along with a leaden sarcophagus that most likely dates from the fourteenth century, according to a report from France's culture ministry last year.

The iconic spire of Notre-Dame, which is being restored by more than 200 scientists, is anticipated to be put back in place by the end of this year. According to the official website of the Paris Tourist Office, the rebuilding project is on schedule to be finished by the end of the following year. This indicates that when Paris hosts the Olympic Games in July and August of 2024, the tourist attraction, which had previously seen 12 million yearly visitors, won't be open.