Deciphering the Iron Provenance on a Medieval Building Yard: The Case of Bourges Cathedral

Maxime L’Héritier,Guillaume Sarah,Philippe Dillmann

doi:10.3390/min10121131

Abstract

This paper presents the provenance study of the iron reinforcements of Bourges Cathedral (13th c.): the links of a 100 m long iron chain, surrounding the eastern parts of the cathedral at the triforium level and 4.5 to 5 m long tie-rods consolidating the arches of the inner aisle at the same level. The analytical methodology is based on the determination of trace rare earth elements analyses by LA-ICP-MS in the slag inclusions of the artefacts and in the slag found on candidate production sites combined with statistical approaches. This chemical approach is crossed with archaeological and historical studies on the monument itself and on the production sites. Ninety-nine iron samples were analyzed on the bars and chains and 238 iron slags from 3 presumed areas of supply. For the first time, iron circulation and trade around a single building yard over a time of 30 to 40 years is studied with a precision never obtained before with historical sources. It shows that mainly four different metallurgical districts, local and more distant, supplied the building yard, mostly depending on the construction phases and also on the types of iron armatures needed.

Highlights

In the past twenty years, several studies have shown that iron was included in the design of many ancient buildings
It is worth to note that a predictive approach by linear discriminant analyses (LDA) cannot be attempted because unknown production areas exist but are not taken into account by the inference
Did the masters of the building yard collect the iron themselves, gathering different productions of unforged iron bars, like in Metz where the burgesses seem to control the iron production and importation in town, notably during the edification of the Mutte tower by the city [21], and had the bars forged by a specialized smithy or a local workshop with a hydraulic equipment? Were the tie-rods forged in the C2 region and reforged or adapted by local smiths with more local sources of iron such as in Troyes? Both hypotheses are valid and endorse the intensity of iron trade to supply this building yard at the beginning of the 13th century. This provenance study of the iron armatures of Bourges Cathedral demonstrates the powerfulness of the trace element approach when it is linked to a solid archaeological investigation, including production area definition, and the study of the artefact to be sourced

Summary

Introduction

In the past twenty years, several studies have shown that iron was included in the design of many ancient buildings It is well-known that major gothic churches were armed with tons of chains, tie-rods and cramps of iron at least since the late 12th century [1,2,3,4]. Sometimes, during glazing campaigns for example, several tons of iron were bought by the building yard from smiths or merchants on a single year [8]. How these large quantities of iron were produced and where they came from are two of the many questions that arise regarding the supply of these building yards and more globally regarding the medieval iron market

Methods

Results

Discussion

Conclusion