Chartres cathedral is a marvel but also a mystery. Nobody knows who designed it or what they were trying to express. Begun in 1200 and finished in 1226, it was the crowning example of the gothic style and marked, Philip Ball suggests in this lucid and resplendent book, a shift in the way the western world thought about God, the universe and man's place in it. Romanesque churches with their vast walls and narrow windows had been dark and inward-looking, and signified, he argues, monastic seclusion. Chartres changed all that. Its walls were diaphanous membranes of glass set in cobwebs of stone. On the outside, flying buttresses propped them up to prevent them collapsing under the soaring vaults of the roof. It was “transparent logic”, a celebration of the light of reason, banishing the old gloom, and progressing from an age when God was feared to one where his works could be understood.

That, at any rate, is the theory. Ball makes no pretence to have thought it up himself. It had been aired in the 19th century, and was elaborated in the 20th by the great German art historian Erwin Panofsky. What makes it plausible is that the school of Chartres, in the decades before work on the cathedral began, had become one of the great centres of European learning, a principal conduit for Arabic science and mathematics, and a pioneer in the rediscovery of Plato, Aristotle and Euclid. It was progressive and humanist, encouraging a rational understanding of the physical world, advancing geometry, and promoting the belief that the universe was a system of eternal order based on numerical proportions.

Is this what Chartres cathedral was trying to say, and if so how were these ideas imparted to the people who actually built it? Ball finds Panofsky's vision inspiring, but sees difficulties fitting it to the facts. Nine successive teams of contractors seem to have worked on the building, so continuity of design must have been imposed by someone, but there is no evidence it was anyone connected with the school of Chartres. The idea of an architect in the modern sense had not yet developed, and decisions may have been taken piecemeal by clerics or patrons or by the master builders, whoever they were. No plans survive, and quite likely none were made, as there was no tradition of architectural drawing. The builders may have carried the design in their heads like mental arithmetic.

There is evidence that bishops were spurred on in their building projects by pride and envy, and it seems possible that the brilliantly ostentatious architecture of Chartres was conceived to satisfy these passions rather than to convey universal rationality. Ball's idea that the building of Chartres began “the age of reason” is the shakiest part of his case. As he points out, the cathedral's most precious relic was the tunic that the Virgin Mary wore when giving birth to Jesus. A later acquisition was the head of Mary's mother, Anne. These rarities attracted pilgrims and wealth, but it is hard to see them as congruent with rational thought in any other respect. More persuasive is Ball's scepticism about the romantic notion that medieval cathedrals were produced by the pious efforts of the whole community. At Chartres, on the contrary, relations between town and clergy were hostile. The church fattened on taxes and tithes (the bishop's income was the equivalent of $1.5m annually) and the building of the cathedral merely served to remind the citizenry of the hierarchy of wealth and power they were at the bottom of. In 1210, they rioted, and a mob attacked the dean's house. In retaliation, the canons excommunicated the whole town. A curious feature of the cathedral is a number of little doorways high up in the walls, and it seems that these led onto wooden walkways, mounted on scaffolding, that allowed the canons to get from one part of the concourse to another without having to encounter their obstreperous flock.

Another popular belief that Ball demolishes is that the workers who built cathedrals were pious folk devoted to the glory of God and elevated above mercenary considerations. No such beings appear in the historical record. The cathedrals were built by wage earners who would go on strike if their interests were threatened, fight rival teams who tried to undercut them, and steal building materials when the opportunity arose. They would also scamp their work unless closely supervised, which may be why their cathedrals sometimes fell down. Beauvais collapsed three times, Troyes four. It even appears, though it seems heretical even to whisper it, that they were not uniformly skilful. Many monastic buildings were brought down in the early 13th century merely by a high wind. Part of the trouble was that accurate calculation of the stresses within a building was beyond the competence even of master builders.

No reader of Ball's book will have any excuse for similar ignorance. His section on how to build your own medieval cathedral, backed up by stylish diagrams, is a model of explanatory writing. It makes clear, even to the least mathematical, how the vast tonnage of masonry in a barrel vault can actually strengthen the building under it, and why a pointed gothic arch is less likely to fall down than a round one. Pointed arches were common in Islamic architecture from the 8th century, and they may have been brought to the West by Muslim workers. The superior masonry skills of Muslims have been detected in the 12th-century stonework of Winchester Cathedral. This is typical of the fascinating data that Ball unearths. His most engrossing section is on the famous blue glass of Chartres. It appears that this was scavenged from Roman and Byzantine sites, shipped to France in the shape of shards, melted down and reused. A treatise by a 12th-century Benedictine describes the practice, and a sunken ship, laden with blue glass, has been found off Turkey. Analysis shows it to contain sodium, from the ash of coastal and desert plants of the Mediterranean, whereas northern European medieval glass, made from beechwood ash, is rich in potassium. The limestone for the cathedral was dug from local quarries, but the blue glass, as a foreign import, was far more expensive. Chartres contains about an acre of it, and it accounted for 10% of the building cost.

The impulse, after finishing Ball's book, to catch the next Eurostar, and head out to Chartres from Paris, is strong. He says that if you sit in the cathedral late in the day, when the tourists have gone, you can believe that the place embodies the last moment when a reconciliation of faith and reason seemed possible. It seems likelier that it embodies a time when no reconciliation of faith and reason seemed needed, because it was assumed that reason, like faith, would lead the mind to God. The famous labyrinth on the floor of the nave has never been explained. But a thing you notice at once is that it is not a labyrinth. There are no possible wrong turnings. The path looks complicated but leads inevitably to the centre. Perhaps whoever designed it meant that life, for the faithful, was like that.

Universe of Stone: Chartres Cathedral and the Triumph of the Medieval Mind by Philip Ball
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