What the Numbers Say
~ Saturday, October 9, 2021 ~
The Chartres labyrinth was measured and built using the Roman foot — 294.45 millimetres — as its basic unit. This is the same unit used throughout the rest of the cathedral. The path length is 888 Roman feet. The diameter corresponds, in whole units, to the building’s master geometric plan. These are not decorative choices. They are the marks left by a measurement system, and they connect the labyrinth to the structure around it in ways that are precise enough to verify.
The labyrinth and the west rose window are the same diameter: 12.89 metres, 42 feet.
This is the most straightforward of the geometric relationships. The west rose window sits above the main portal, at the far end of the nave from the choir. The labyrinth is in the nave floor, roughly a third of the way in from that portal. They are not near each other. They are, however, exactly the same size, and they were designed to be: if the western façade were folded flat onto the nave floor, the rose window would land on the labyrinth. The cathedral’s plan required this — the labyrinth’s centre corresponds to a primary anchor point of the building’s geometric layout.
The measurement system
The Roman foot (294.45 mm) was the standard unit for the Chartres builders. The path length of 261.5 metres converts to 888 Roman feet. The centre of the labyrinth is 2.942 metres in diameter — exactly 10 Roman feet. The six-petalled rosette within it uses divisions of 3, 5, 7, and 10 units. These are the proportions of a deliberate geometric design, not of rough approximation.
The number 888, in a medieval symbolic context, carries additional weight: it is the numerical value of IHSOUS — Jesus — in Greek isopsephy, the practice of summing the letter values of a name. Whether the builders chose this path length to encode that number is not provable. That the path length arrives at this figure in their own measurement system is a fact.
The lunation ring
Around the outer perimeter of the labyrinth, a ring of carved stone cusps — lunations — runs continuously except for the gap at the entrance. The standard count is 113 visible cusps, or 114 if the missing cusp at the entrance is included. The figure of 28 cusps per quadrant (four quadrants × 28 = 112, near to 113) has been read by several writers as a reference to the lunar month.
Jeff Saward, whose technical work on the Chartres labyrinth is the most careful published account, is sceptical. He notes that medieval astronomical instruments give the lunar cycle as 29.5 days, not 28, and that the connection between the lunation cusps and the lunar calendar has never been demonstrated with precision. I record both the measurement and the scepticism, and leave the question where he left it.
The solar instrument in the same building
The labyrinth is not the only precise astronomical instrument in Notre-Dame de Chartres. In the north transept, a metal pin is set into one of the upper windows at a specific height. A corresponding white flagstone is laid into the floor at a calculated distance. At solar noon on the summer solstice, the beam of light passing through the pin strikes the flagstone exactly.
This gnomon — a solar noon marker — is well documented and undisputed. It was built into the cathedral as part of its original structure. Whether it served a practical function (calibrating feast days, regulating the canonical hours) or a symbolic one is less clear. It is, in any case, evidence that the Chartres chapter was interested in precise solar measurement, and that this interest was embedded in stone during the same period as the labyrinth.
I noted in the Cappadocia series, in an earlier piece on orientation anomalies in the Ihlara Valley cave churches, that three chapel altars there deviate from the standard east-facing orientation by exactly 14 degrees. The angle between the Chartres labyrinth’s north–south axis and the solar gnomon’s noon-line is geometrically close to the same figure. I record this without pressing it. Fourteen degrees appears in more than one context in the sacred architecture of the medieval Mediterranean world. Whether the appearances are related is not something I can establish from the available evidence. I record it as a dimension worth noting.
In this series
- The stone path that no one recorded — the Chartres labyrinth
- The labyrinths they destroyed — Reims and Auxerre
- The Jerusalem theory and its problems
- A rubric for the eve of Candlemas
Sources
- Technical data of the Chartres labyrinth (mymaze.de)
- A. García-Avilés, “Justification about the existence and location of Chartres’ cathedral labyrinth based on astronomy and geometry,” Cogent Arts & Humanities (2019)
- Craig Wright, The Maze and the Warrior (Harvard University Press, 2001)
- Jeff Saward, Chartres Cathedral Labyrinth FAQs (Labyrinthos Archive)