As Europe emerged from the Romanesque, undocumented Norman and Benedictine influences manifested a "Gothic" style of cathedral building, conflating church building with exotic cosmological ideas involving sacred geometry and astro-harmonic symbolism. The prime exemplar of Gothic is perhaps the Cathedral of Chartres, now shrouded in many mysteries including who could have built such a masterpiece. John James [1] reports that records concerning its construction were lost in the century following its completion.

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Figure 1 The Western Towers of Chartres Cathedral

The ratio between the twin towers is the same as that between the 12 month to 13 month lunar years, the latter being the same astronomical period John James proposed as intended for the whole length of church (then in Std Geo Royal feet.)

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Figure 2 John James interpretation of the overall design was
an embodiment of 12 and 13 month lunar years.

1. The Master Masons of Chartres. James, John. Routledge and Kegan Paul: London 1982.

"The most important astronomicial calculations undertaken in the middle ages were to compute accurately the dates for Easter. Though dependant on the moon, the dates still had to keep in step with the cycle of the solar year. This hey did through a simple formula, where for two years running they fixed Easter from the short year of thirteen [twelve]lunations, followed by one long  or embolismic year of 384 days which, with suitable adjustments, brings the Easter cycle back into phase with the sun." 111.

Two times 12 (=24) plus 13 equals 37 lunar months, three of those 111 months and six such periods equal 235 months, the duration taken for the 19 year (Metonic) anniversary of sun, moon and stars. In the Julian calendar of that date, an extra month every three lunar years could keep Easter later than the Spring Equinox. Meanwhile, 37 lunar months equals three Saturnian years of 364 days thus synchronising Easter with the seven day week, since the rubric for Easter established by the synod of Whitby was "the first Sunday after the first full moon after the equinox." (see also our articles)

Another possible view, taken here, is that the heights of these towers, were in root geographical roman feet of 0.971003 ft since 344 ft (as quoted) is 354.367 x 0.971003=344.09142 ft. [2]

2.This view became possible due to Ernst Levy's appendix to Simson, Otto von. The Gothic Cathedral. Bollingen: Tennessee 1956. called On the Proportions of the South Tower of Chartres Cathedral. This was removed from later editions)

In a previous article, Chartres: Relation of Western Towers to Gothic Floor Plan, Keith Crichlow's ideas were explored: that the two towers were (a) symbolic of the sun and the moon (as per their popular naming) in their heights but that (b) these heights also figured a horizontal lengths in that the Rose Window equated to the Labyrinth and the aisle lengths might correspond to the linear development of the cathedral's floor space, from a common line at the base of the towers. Two key questions emerged:

  • Do the Tower lengths correspond to features along the floor plan?
  • And why would such a concept have been employed at Chartres?

Firstly one can see (figure 3 below) a correspondence between the façade and the floor plan: The single lunar month difference between 12-month and 13-month lunar years corresponds to the radius of the Rond. Though Critchlow thought the two towers were 365 and 354 feet high (the sun and moon towers in both name and measure) the ratio in their heights of ~1.08 is not the ratio between the solar and lunar years but (as stated) is 12:13, the ratio between the 12 (normal) and 13 month (embolismic) lunar years.

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Figure 3 Identifying the 1.08 ratio in the floor plan
and locating the labyrinth  as mirroring the Rose Window

  • Do the Tower lengths correspond to features along the floor plan?

If the metrology within the cathedral had a starting point on entry to the Nave one can reach the start of the Apse as delimiting one lunar year using a new measure, a cubit of 1.77 feet*** . One hundred of those cubits equals 354 half cubits whilst the diagonal across the Nave and Choir is then 360 half cubits eight times 45, the harmonic root of Adam (see figure 4 below).

[***Root version of the cubit of Al Mamun. NEAL. 2000. 92.]

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Figure 4 Metrological Interpretation of Chartres Floor Plan,
organised according to astronomical time

The first pillar of the Ambulatory defines the 13 month year and before that lies the solar year (as red diagonal of a purple four-square rectangle) on an arc so as to touch the central ceiling boss, which boss then marks the solar year of 365.2422 days as central to the Apse/Rond (the sun central to the solar year and solar system.)

The embolismic year defines side length of a 24 by 7 rectangle (in blue) to the first pillars of the Rond, a proportion of chromatic semitone 25/24 to the lunar and a 25 unit diagonal of 400 days (see below). The width of this rectangle is 112 half cubits (16 times seven), the same as the number of cusps around the outside of the Labyrinth.

  • And why would such a concept have been employed at Chartres?

The answer lies in the diabolical functional approach to calculating Easter and why the Synod of Whitby should have fought the Celtic church so hard to have such a labyrinthine definition for Easter. I highlight the word functional because the method of calculation is just that and carries no understanding of the phenomena behind the two lunar years which the twin towers of Chartres represent also relating to the Easter of the western church.

Every solar year there are 12 and 7/19th lunar months and this means that after nineteen years there are 12 x 19 = 228 + 7 = 235 lunar months, the Metonic count. These seven extra months are being distributed so as to become 12 + 12 + 13 = 37 lunar months so that six of these are 222 lunar months. Add one month and one obtains the Saros eclipse period of 223 lunar months. Add thirteen months and one obtains the 235 lunar months of the Metonic. The Metonic has seven embolismic years of 13 months because of the 7/19th of a lunar month per year. Since the Embolismic is a normal lunar year plus one, then seven lunar years can be taken off the 12 x 19 leaving only twelve, used for the mixed counting scheme with seven longer years.

Whilst towers, aisles and their metrology can be symbolic, we saw in the earliest Greek temple (the Heraion of Samos) that its columns (thought merely symbolic or supportive) had an astronomical counting function. The twelve columns up to the rond seem to offer a counting function but instead it is the bosses of the gothic arches above each stall of the aisles that appears to have a celestial counting function as equalling a single lunar eclipse. There are twelve bosses/stalls in each side aisle and in the central nave/crossing/ choir able each to count twelve lunar months. If the central twelve are linked to the single boss of the Rund, then the central hall plus Rund add up to the Embolismic year of thirteen lunar months and, with the side aisles, a total of 37 lunar months can be counted, as shown in figure 5.

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Figure 5 Chartres Cathedral as Device
for Counting Astronomical Time

Since a count of the Saros and Metonic requires a common basis of six such counts of 37 lunar months then the six columns of the Rund appear to give a mechanism for knowing where the count has reached. Having made six counts of 12 + 12 + 13 = 37 x 6 = 222 then counting the Rund gives the Saros of 223 lunar months whilst then counting the central twelve gives the Metonic period of 223 + 12 = 235 lunar months or nineteen years.

One can say that the arrangement above resembles an abacus in form and also that the notion of placing the lunar months in the highest point of each ribbed ceilings boss has considerable symbolic merit that might even point to how the boss functions to keep the ceiling from falling; like an ethereal equivalent of a column, the boss is connected to the sky.

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Figure 6 The Bosses of Chartres Cathedral Choir and Rund
CCAS by Marianne Casamance