Notre-Dame de Paris was the first building of its kind in which the builders relied on iron reinforcements throughout the structure

Iron armatures in Notre-Dame: staples of the top walls (southern nave looking on the angle of the southern transept).

Several thousand metal staples were used to bind the stones together

At the time of its construction in the mid-12th century, Notre-Dame was the tallest building of its kind, reaching a height of 32 m. Previous research suggests that this record was made possible by combining a number of architectural innovations. However, despite extensive use of iron reinforcements in more recent cathedrals and in efforts to restore old buildings, it has been unclear what role iron might have played in Notre-Dame’s initial construction.

For secular buildings, the Romans had already used clamps made of iron or lead between the stones.

Now, the 2019 fire and subsequent restoration have allowed Maxime L’Héritier of Université Paris 8, France and colleagues to investigate previously inaccessible parts of Notre-Dame. The researchers obtained samples of material from 12 iron staples used to bind stones together in different parts of the building, including the tribunes, nave aisles, and upper walls. They applied radiocarbon dating as well as microscopic, chemical, and architectural analyses to better understand the staples. The findings are published in the open-access journal PLOS ONE.

Iron armatures in Notre-Dame: staples (red) inside the monolithic columns of the nave.

These analyses suggest that iron staples in large numbers were indeed used in the earliest phases of construction of Notre-Dame in the 1160s, making it the first building of its type to have relied on such metal reinforcements throughout its structure.

In combination with other archaeological and historical knowledge for that time period, the analyses also provide information that could help deepen understanding of the iron trade, circulation, and forging in 12th and 13th century Paris.

For instance, many of the staples appear to have been produced by forging together pieces of iron obtained from a number of different supply sources.

The authors add: “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 medieval builders used several thousand iron staples throughout its construction.”

L’Héritier M, Azéma A, Syvilay D, Delqué-Kolic E, Beck L, Guillot I, et al. (2023) Notre-Dame de Paris: The first iron lady? Archaeometallurgical study and dating of the Parisian cathedral iron reinforcements. PLoS ONE 18(3): e0280945.

Photos: PLOS One

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(23.03.2023, USA: 03.23.2023)