using metal in gothic cathedral construction

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gothic cathedral and church construction

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But buttressing was often not enough, especially if a buttress was mis-positioned - easy enough to do before the days of civil engineers trained in Newton's laws of physics. So to correct impending collapses, metal was used to strengthen and reinforce the cathedral's structure, as well as providing additional support. Iron ties held arches together, while a girdle made of forged iron 'links' held the cathedral's waist (usually at the triforium level) in trim.

This page will discuss and illustrate how metal was and is an integral part of a structurally sound cathedral's construction.

Keep in mind that the development of these structures was greatly mediated by trial and error. Of course, that is the way engineering develops, as can be seen to this day. These methods of using iron have been used in many cathedrals around Europe. Some indications can be found in this, rather sloppy, paper: The role of iron armatures in Gothic constructions: reinforcement, consolidation or commissioner's choice.

forging the iron

The Abbaye de Fontenay at Montbard in the département of Côte-d'Or. Founded and run by Cistercian monks, the abbey complex includes the late 12th-century forge building. Over 50 metres long, it probably housed two furnaces, with several mills operating hydraulic hammers.

The wrought iron supplied to Amiens cathedral and others was probably forged in a Cistercian workshop of this type. This forge is about 300 km from Amiens cathedral. Amiens cathedral was built between 1220 and 1266.

[The Abbaye de Fontenay/Fontenay Abbey is at Montbard 21500, tel. n°: 03 80 92 15 00, fax n°: 03 80 92 16 88.
The Abbey is open every day of the year, but times vary depending on the season.
Full details, including entrance fees, are at the Abbey website, they advise checking it before finalising your visit.]

chainage or stabilising rods, and buttressing

To help protect the cathedral from literally falling apart from the strains generated by building such a large structure that led to it being rather unstable, chains of iron stabilising rods [chaînage, chainage] were added, generally hidden galleries and passages.

There were many combinations of rods, bars, ties that were connected to, and connected by, claws, clamps, crampons, brackets; these being held together by dowels, gudgeons, pins and wedges. Altogether these would be classified as chaînage.

CHAÎNAGE: This word applies to wood stringers, or to successions of iron hooks laid like links in a chain, or even iron bars or rods, laid horizontally along the triforium, all designed to prevent spreading and dislocation of masonry construction.

The building of Amiens cathedral, a huge cathedral only capped in height by Beauvais, was much affected by the then nascent knowledge of structural engineering, and by the ambitions of the builders and the people who commission the construction. The flying buttresses were not always sufficient, or were not placed to apply a counter pressure in the right position to prevent the stone shifting so cracks appear, columns to bow and arches threaten to collapse.

To correct the problems that appeared, the builders at Amiens took two main steps. One was adding better positioned buttressing. The original flying buttresses had been placed so their point of reinforcement was too high, and so not effective. Additional buttressing was added later to correct the problem.

Double buttressing at Amiens

The original buttressing to the south-east crossing of the transept and nave had been designed to support both the clerestory wall and the vaults. However, the buttresses in this area were placed too high to give full support to the vaults, so they were supplemented with a lower strut. For a more detailed discussion see buttressing and chainage at Amiens cathedral.

The second method for correcting the cathedral's structural problems was giving the cathedral a girdle, at first in wood. This was later replaced with an iron armature, probably forged at the Abbey of Fontenay.

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As the diagram above illustrates, the iron 'girdle', the ceinture de fer or iron belt, holds together the arches between in the nave and the two sides of the transept at Amiens cathedral. The 'girdle' is made up of solid iron rods, linked together by strong links, and set firmly into the fabric of the cathedral's stone structure at the end points. The rods were up to 4 metres long and had a cross-section of 4 by 8 cm. This iron chain, or chaînage, lies on the floor of the triforium running around the cathedral above the main bay arches. As can be seen in the illustration at the head of this section on chaînage, this is just above where cracks have appeared as parts of the cathedral shift apart.

problems with chainage

Originally, the chainage that prevented arches collapsing from outwards pressures were made from wood, included in the cathedrals as they were built. In some cathedrals, like Saint-Denis and Notre Dame de Paris, there was such a retaining 'girdle' at each level of arches. Viollet-le-Duc, when supervising the dismantling of these cathedrals before restoring and rebuilding them, found quadrilateral-sectioned 'tunnels' through the cathedral structure left by the wood that had rotted away.

As a result, and as the making and manipulation of iron developed, the wooden chainage was supplemented and replaced by iron. However, iron would also have its problems, rusting over time, or as Viollet-le-Duc described it,

"To give an idea of the power of the swelling iron, when it passes to the state of oxide or iron carbonate, we will observe that the chaining positioned below the supports of the large widows of the Sainte-Chapelle, by swelling, lifted the foundations composing the sills and mullions they support, to the point of buckling these mullions and breaking them at some points, although they were of great strength."

This rusting was lessened by enveloping the iron with lead. A more modern rust protector for iron is red lead, that until recently could be seen protecting large structures such as the Golden Bridge at San Francisco and the Forth bridge in northern England. The red lead protection has now been replaced by modern alternatives.

chainage at Sainte-Chapelle

Interestingly, the chapel of Sainte-Chapelle in Paris incorporated a form of iron reinforcement, with two ‘chains’ of hooked bars encircling the upper chapel, the main part of the structure. Further, there were iron stabilisers across the nave (with a vertical tension bar).

Drawing by Lassus of reinforcing bars, with bars and links emphasised

Also, an impressive eight-pointed iron star helped hold the apse together. Its iron bars radiated from a central collar. (The drawings above and below were made by Jean-Baptiste-Antoine Lassus during the restoration of Sainte-Chapelle.)

Drawing of eight-ponted iron star by Lassus

Originally, the iron bars were much smaller, because the technology could not produce enough iron at one time to make longer bars. In those early days, the iron bars (called crampons) hooked one into the next.

Crampon chain at Sainte-Chapelle, illustration from Viollet-le-Duc

As well as crampon bars with a hook at one end and eye at the other, there were also bars with two eyes or two hooks to enable all possibilities on connection, depending on the circumstance.

stabilising and reinforcing tie rods - Saint Quentin, Westminster

Iron stabilising bars in Westminster Abbey [indicated with blue arrows]

Because of the rather dodgy stability of the gothic buildings, later additions of iron stabilisation can be seen in many cathedrals, for example at Westminster Abbey and in the cathedral at Saint Quentin.

The tie rods at Saint Quentin are placed higher, nearer the apex of the Gothic arch, than those at Westminster Abbey. A lot of construction development, changes and even improvements, were a matter of trial and error.

Reinforcing rods across the arches at Saint Quentin cathedral

It is of interest to note that, at Saint Quentin, the apse tie-rods were removed at the end of the 19th century, while those in the nave were kept. After the First World War shelling, the apse vaults collapsed, while for those in the nave the ribs survived, though the webs between them were damaged. After the cathedral was restored, the nave tie-rods were removed.

Chartres roof space : le charpente de fer

charpente :

French for structure, framework  

de fer :

French for 'of iron'

On June 4, 1836, following the carelessness of plumbers who were making repairs, a fire broke out in the roofing timbers of Chartres cathedral. The fire spread quickly, destroying the wood frame, the forest, and the cathedral's lead roof. Fortunately, the fire did not advance into the bell tower. There, the great bell was not harmed, sounding for half an hour. Many lower bells were lost, to be replaced in 1840 and 1845 by those still rung today.

The roof was replaced by a beautiful iron frame and a copper roof, built in metal for future safety and for economy, like the partial roof at Southwark Cathedral, London built during the restoration of 1822-25, and the cupola at Mayence [Mainz in Germany], built in 1827 (?). When built, the span over the cathedral's crossing (where the nave crosses the transept) was the largest of any iron-framed construction in Europe. The iron frame looks like a huge boat overturned. The framing has joists of wrought and cast iron, connected by rafters that ensure the rigidity of the structure. During the winter storm in 1997, a portion of the roof was torn and was long covered by tarpaulins. By December 2009, renovations were completed. The metal frame, having suffered from corrosion and expansion due to temperature changes, has been partially restored between 1995 and 1997 by Guy Nicot, chief architect of historical monuments.

The roof structure of Chartres cathedral is one of the oldest iron structures in France. It was built in 1837 by architect Emile Martin and locksmith Mignon. The structure was made combining wrought iron and cast iron. The principal curved beams rising to meet at a point, are cast iron. They support a superstructure in iron carrying the roof of copper tiles. The iron horizontal rafters are connected by several rows of double spacers, forming a very rigid system. The system of segments bolted together and crossed by cast iron bars is inspired by some iron bridges built in England, such as the Severn Bridge at Coalbrookdale, built in 1777. On such constructions, the resistance of cast iron in compression enables the creation of arches. The steep slope of the rafters limits the bending forces, while a series of wrought iron rods take up a portion of the lateral thrust.

	Left : Roof framework at transept crossing. Image credit: anonymous
	Left : Roof framework over the nave. Image credit: http://crecyjourdhui.centerblog.net

Another method can be seen at Noyon cathedral with the roof off and the rather more tidy concreting, the modern idea of rubble. Of course, this much reduces the fire risk from the traditional and medieval forest.

Rouen lantern tower

The central lantern tower, combined with its spire, is the tallest in France at 151m or 495 ft. Building started in the thirteenth century, the spire being raised in the sixteenth century. The present cast iron spire was raised in 1876 to replace the previous wooden spire, covered in gilded lead, which had been placed there in 1544. That wooden spire had been destroyed by fire in 1822.

From Rouen, It’s [sic] History and Monuments, A Guide to Strangers by Théodore Licquet, 1847, reprint 2007

“We cannot give too many praises to the zeal of M. de Vansay, prefect of the department at that time: the misfortune happened on the 15th september, and already on the 26th of the same month, the government having been informed and solicited by that magistrate, ordered M. Alavoine, one of the best architects, to go to Rouen, and confer with the prefect on the means of remedying the havoc caused by the fire. Early in the year 1823, the roofs of a aisles had already been repaired; and a portion of the nave had been covered with lead, by the 15th march of the same year. The roofs of the choir and of the whole transept, were also soon repaired; but, for these parts, a copper covering was preferred as being more solid and less liable to be destroyed. The raising and renewing the lantern was terminated in 1829.

“From this new platform, the pyramid will rise majestically in the air, and of it we already discover thirteen floors (the pyramid will be completed with one more), each of four metres fifty centimetres, that is to say a height of fifty eight metres, or about one hundred and eighty feet. The spire of the church was first erected of stone but was overthrown by the electric fluid, after that, it was twice built of wood, and both times it became the prey of the flames; to rebuild it with wood would have been gathering materials for a third fire, but now it is made of cast iron and in open work. At the summit of the spire, there will be a small lantern surrounded by a gallery for the purpose of meteorological observations. The total weight of the spire when completed, will be 600,000 kilogrammes, or about 1,200,000 pounds. It is composed of 2,540 pieces, not including 12,879 iron pins[13]. Lastly, this magnificent pyramid will reach an elevation of 436 feet; that is to say 40 feet higher than the former, and will only be 13 feet less than the highest pyramid of Egypt.

“[Footnote 13: The whole of these pieces of iron were cast at the foundry at Conches, a small town, which is situated at about twelve leagues from Rouen, and the expense is valued at 500,000 francs.]

Elise Whitlock Rose commented about the lantern tower:

"No truly artistic ideals disturbed the minds of the XIX century builders. They remembered only the perils of lightning and fire, and raised a spire which had every justification of sense and economy, but which, from an architectural point of view, is a hideous monstrosity. Unfortunately, it is of iron and will probably persist, to show to succeeding generations that the early XIX century was no less barbarous in its utilitarianism than the XVIII century was in its pseudo-classicism."
[p.353, Cathedrals and cloisters of the Isle de France, vol II by Elise Whitlock Rose]

metal at beauvais and bourges

"In Beauvais, a number of the metallic tie-rods supporting the flying buttresses bear graffiti from the eighteenth century, potentially indicating that the metal may have been a later addition. However certain pieces proved to date back to the beginning of the construction process (around 1225-1240 AD), suggesting that in order to succeed in erecting the world's highest Gothic choir (46.3 meters), iron was combined with stone from the initial design phase."

The Germans smashed Beauvais cathedral in 1940, as can be seen in this image. The upper flying buttresses were destroyed (see right).

Therefore, I am unsure quite what is being claimed here. Maybe some of the bars had been recovered from the rubble.

"In the Bourges cathedral choir, which is older (1195 - 1214 AD), an iron chain surrounding the choir proved to be contemporary with construction. Nevertheless, it skirts a group of columns, while passing under some others, which clearly shows that it was not part of the original plan, but was integrated during construction. This analysis confirms that cathedral building yards were genuine laboratories where builders, coming from various trades, tested construction techniques to meet architectural challenges."
[From press release for Gothic cathedrals blend iron and stone]

"[At the upper triforium level of the cathedral at Bourges, an] iron chain is embedded in the base of the passage, traversing the the inner sections of the vertical supports at main triforium level. The links, square bars about 1m. 30 in length, are set in a shallow trough that runs the whole length of the passage. It is impossible to know whether the chain is tied by vertical clamps to the wall responds or, indeed, whether it actually functions in tying the supports together." [p.84]
—
"It is interesting to note that the iron chain embedded in the main triforium of the chevet was not prolonged into the nave." [p.131]
[From Cathedral of Bourges, and its place in Gothic Architecture]

Plan of Bourges cathedral

related documents

cathedral giants - Amiens and Beauvais cathedrals
Le Mans and Bourges cathedrals - medieval space technology

other metals : bronze, lead, cast iron

Other metals commonly used in cathedrals include

lead for roofs and stained glass windows;
bronze for monuments; and
cast iron for the likes of rood screens.

Unfortunately, these metals are often coveted for war-making or profit.
Thus, during the French Revolution, roofs were stripped and the lead used for ammunition such as musket bullets that were ball- or disc-shaped, cylindrical or conical-shaped bullets were not introduced until 1826. This left cathedrals open to the elements.

Bronze monuments were melted down to make cannons, or sold for decorations; and
iron was looted to reuse the metal. for mundane purposes.

lead in cathedrals

Lead in cathedrals is frequently used to cover the roofs. Cathedral roofs are often intricate, with complicated shapes and curves. Lead is manipulable, and so is a very effective, if heavy, protection from 'the elements'. However, lead has always been an attraction to thieves and vandals.

Lead is also used as the grouting, or caulking, that holds the myriad pieces of coloured glass that make up the glorious windows of the great cathedrals of France. The modern piece of lead came [right] would have panes of coloured glass slotted in on either side.

But here described are other widespread, yet not much discussed, uses of lead in cathedral construction - for protecting iron bolts, and for levelling the footing of arches and pillars. Iron rusts easily unless protected from the damp air. Using lead to protect the iron chainage has been mentioned above, but this is only one example of iron protection. The others are hidden.

Iron bolts were put between the blocks of stone making up pillars and arches to reinforce them against movement [see left]. However, there were two problems: the iron rusting, and the difficulty in chiselling exact holes in the stone to hold the bolts. The solution was to encase the rod in molten lead, that also surrounded the bolt in its hole, the bolt becoming immovable when the lead solidified.

Lead also provided a easy-setting mortar between relatively rough-cut stones, to ensure the stones have a good seating the ensemble of arches or pillars [see right]. In some situations, molten lead was poured into a pre-fashioned 'tunnel', so molten lead could be introduced into the centre of a wide column or arch. The entrance hole was then stopped by a stone plug.

bibliography

	Dictionnaire raisonné de l'architecture française du XIe au XVIe siècle by Eugène Viollet Le-Duc.
	press release for Gothic cathedrals blend iron and stone, CNRS, Paris. This document was published in the Journal of Archaeological Science in January 2015 with a longer title. Consolidation or initial design? Radiocarbon dating of ancient iron alloys sheds light on the reinforcements of French Gothic Cathedrals by Stéphanie Leroy, Maxime L'Héritier, Emmanuelle DelquéKolic, Jean-Pascal Dumoulin, Christophe Moreau, Philippe Dillmann. Journal of Archaeological Science vol. 53 (January 2015), pp. 190-201. DOI: 10.1016/j.jas.2014.10.016 Available as a .pdf from academia.edu. You sign in (abelard.org used the facebook button), the press "READ PDF" below. The pdf may not appear immediately.
Cathedral of Bourges, and its place in Gothic Architecture by Robert Branner
	The MIT Press, 1989 ISBN-10: 026252130X ISBN-13: 978-0262521307 amazon.com amazon.co.uk
L'homme et la matière : L'emploi du plomb et du fer dans l'architecture gothique by Arnaud Timbert
	Editions A & J Picard, large pbk, 2009 ISBN-10: 2708408356 ISBN-13: 978-2708408357 amazon.com £28.62 [amazon.co.uk]

end notes

1. Now (2016) While engineering may be more sophisticated, trial and error methods can still be seen with the progress in the development of privately financed and other rockets and space craft.
   
   
2. The monks were removed from the Abbaye de Fontenay by the French revolutionists, and the abbey was sold. Fontenay was bought in 1820 by paper maker Elie de Montgolfier, nephew of the balloons inventors. Since then, the property has remained in the hands of the Montgolfier-Aynard family. An annual mass is held on 21st September to commemorate the consecration of the Abbey in 1147.
   
   
3. It is often assumed by those knowing some French that charpente is derived from char-pente,where pente means slope. However, charpent comes from the Latin word carpentum, a two-wheeled chariot.
   In Gaulois, charpente described a chariot, a small cart, made of an assembly of bits of wood.
   The word charpente comes from the Mérovingien Latin, carpenta, a piece of wood.
   [Etymological leads thanks to DVH.]
   
   
4. The iron roof was above the choir. It was built by George Gwilt Jr., 1785-1856.
   
   
5. The cupola was removed in 1870 because it was too heavy. Other early examples of ironwork usage were St. Isaac's cathedral in St. Petersburg, Russia, and the leaning tower of Nevyansk, Russia. The latter was probably built a hundred years earlier. However, these two were also only cupolas.
   
   
6. char (d'assaut) nm.

   in modern French, a (military) tank.
   An associated word is charabanc, from the French char-à-banc, a cart or wagon with benches on/in it, much used in England between the wars [1920s to 30s] - an open-roofed coach, most often carrying holiday-makers.
   
   

7. The spire at Rouen also has 812 steps inside it. These could be climbed, if you have the nerve, but we are not sure whether this is still permitted.
   
   
8. Bloom or loop (from old Frankish luppa or lopp)
A shapeless mass.


9. The hammering by the hydraulically powered hammer resulted in an oblong-shaped iron block that was similar in appearance to the shingles used for roofing.

cathedrals – introduction: reading stained glass
gothic cathedral and church construction
cathedrals, an illustrated glossary
Chartres - wonder of the world
Notre Dame de Paris, Paris
lantern towers of Normandy and elsewhere
history of ugly stained glass: Auch, Bazas, Dreux
Auch cathedral choir and stalls
Rouen and Monet
Dax and church iconography photographs, Dax
Bazas - iconography and architectural styles
Poitiers, neglected masterpiece photographs, Poitiers / photos 2
Angers, heart of the Angevin Empire photographs, Angers
Laon, the midst of the gothic transition, with added oxen photographs, Laon
Saint-Jean-Baptiste de Lyon
Notre Dame of Lausanne
Senlis - how a typical cathedral changes through the ages
Saint-Bertrand-de-Comminges - the cathedral of the Pyrenees
Cathedrale Saint-Gatien at Tours

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