The wrought iron bar chain that saved the Amiens Cathedral from collapsing

The Amiens Cathedral, listed as a Historical Monument in 1882 and included in the UNESCO World Heritage List in 1981, is a reference in its style and also has a series of curious elements that make it particularly interesting. One of them is the famous labyrinth that paves the floor of the nave; another, the projection of night light on the facade to give it a spectacular polychrome appearance; there is also a relic as unusual as the skull of Saint John the Baptist. But perhaps the most peculiar is the wrought iron bar chain, which is said to be of Spanish manufacture, with which the building was surrounded to prevent it from collapsing.

Amiens is a small French town on the Somme river whose main tourist attraction, apart from the house museum of the writer Jules Verne, is the aforementioned cathedral church, a jewel of classical Gothic built from 1220 over the ruins of a previous Romanesque temple that had been destroyed by a fire caused by lightning.

The idea of erecting something exceptional was not only intended to compensate for this loss but also to give adequate shelter to what was considered one of the most important relics in France, the forehead of the skull of Saint John the Baptist, which a Crusader knight had brought from Constantinople two decades earlier, turning the place into a destination for crowds of pilgrims – especially epileptics who hoped to be healed from what was then called Saint John’s disease.

The architect chosen to design the new temple was Robert de Luzarches. However, he did not stay long because, at the request of King Philip II the Augustus, he left the job in 1228 to take on the construction of another famous cathedral, Notre-Dame of Paris. By that time there was already enough in place because the work was done quickly, thanks to the fact that the economy of Amiens was going through a buoyant period as it had a monopoly on a plant used for dyeing and thus creating a growing bourgeoisie that collaborated financially with important donations.

Robert de Luzarches left after two years and was replaced by Thomas de Cormont, possibly a disciple of his, who would later take charge of another important Parisian church, Sainte-Chapelle. Cormont led the work until 1228, when he died and was succeeded by his own son, Renaud. It was he who completed the nave and closed the walls of the vaults, starting the transept and raising the façade.

Around 1240, trouble came. The economy shrank, money became scarce and works slowed down for eighteen years. Paradoxically, a fire gave a new impulse to the project, the choir was finished in 1269 and the whole thing was completed in 1288. The towers of the façade were missing – they were never built – but the cathedral was already operational and, in fact, in 1385 the wedding between King Charles VI and Isabella of Bavaria-Ingolstadt was held there.

However, there were still minor additions. For example, eleven side chapels which, as they did not appear in the original plan, required the buttresses of the naves to be moved outwards and consequently the flying buttresses to be lengthened. This was a clumsiness that became a danger, since these buttresses, which were responsible for counteracting the pressure of the choir loft, were too weak for the pressure exerted by the enormous height of the arcades (42.3 metres) of the naves of the triforium. To solve this, they were reinforced with a second line of lower flying buttresses… which caused cracks to appear.

The double row of flying buttresses in Amiens / Image: Jacques 76250 on Wikimedia Commons

Everyone was aware of the risk of collapse, since in 1284 the dome of the neighbouring Beauvais Cathedral had collapsed from a similar cause, when two buttresses of the apse gave way. This was the result of rivalry, since until then the naves of Amiens cathedral were the highest in Europe and Beauvais cathedral was built to overcome it.

In 1573 it suffered a second collapse that left it deeply battered (to this day, it is still in a very delicate state), hence the subsequent surrounding of the structure with iron clamps to act as containment, although this took away the flexibility of the whole and cracked it. It was a solution precisely borrowed from the one applied by Pierre Tarisel in Amiens.

An example of chainage, from Sainte-Chapelle (Eugène Viollet-le-Duc) / Image: public domain on Wikimedia Commons

Around 1482, Tarisel had replaced the late Guillaume Postel as master builder and analysed the state of the building, considering the second pillar of the choir and the outer walls to be a danger. The pillar was secured in 1497 and six years later the same was done with the others. But the question of the outer wall was missing, which, when cracked, was threatening to collapse due to the thrusting force of the choir vault. Tarisel solved it by wrapping the perimeter almost completely with what they call in French chainage, an iron bar chain that passed through the triforium and the arms of the transept.

This chain, a kind of belt made of different types of wrought iron bars (a material chosen for its ductility), was ordered from Spanish forges because that was where the most highly prized iron was made at that time. Or so says one version, since another places the origin in the Abbey of Fontenay, a Cistercian monastery in the Burgundy region so large and prosperous that it even had steel forges. In any case, it was a series of rods, bars, clamps, straps and staples which, once transported to Amiens, were riveted into the red-hot stone, tightening them as they cooled to form the containment strip.

Detail of the iron bar chain of the Amiens cathedral / photo Ludovic Bellot-Gurlet

In fact, this was not a new idea; in the past, this type of reinforcement was mostly made of wood, which caused additional problems due to the tendency of this material to swell with humidity and even rot. Of course, iron also had its drawbacks: not only did it rust (something they tried to prevent by wrapping it in lead) but, like wood, it could swell. Even so, it was a system that spread from then on, given its success at Amiens.

After everything was completed in less than a year, and considering that the cathedral is still standing, it seems that they made the right choice. In fact, the bar chain is still in place, as it is in other buildings of the same type such as Chartres, Sainte-Chapelle, St. Quentin or Westminster Abbey. In Beauvais it was removed in the 1960s but had to be replaced, reinforced with steel, as the wind made the structure oscillate too much; no one wants to risk another disaster.

Sources: La construcción medieval (Eugène Viollet-le-Duc)/Using metal in gothic cathedral construction ( e historia en la Edad Media. Tiempo, espacio, instituciones (Enrico Castelnuovo y Giuseppe Sergi, eds)/Summa artis, historia general del arte (Manuel B. Cossío y José Pijoán)/Wikipedia