Day-inch counting at the Manio Quadrilateral

It is 10 years since my brother and I surveyed this remarkable monument which demonstrates what megalithic astronomy was capable of around 4000 BC, near Carnac. The Quadrilateral is the earliest clear demonstration of day-inch counting of the solar year, and lunar year of 12 lunar months, both over three years. The lunar count was 1063.125 day-inches long and the solar 1095.75 day-inches, leaving a difference of 32.625 day-inches. This length was probably the origin of a number of later megalithic yards, which had different uses.

Figure 1 The assumed geometry between the lunar and solar day-inch counts after the 2010 survey of the Quadrilateral. The underlying site plan is Thom’s, largely superceded by that used in figure 3.

Working out the difference in length of two periods was a surprisingly significant act since the difference was key to working out the normalized form of the right triangle which identifies the unique superparticular ratio expressed by the two lengths. Dividing three lunar years by the excess, of 32.625 day-inches, one would obtain the AMY, the true ratio between the sun and moon which is just less as 32.585 inches. But doing that division was well nigh impossible in the megalithic. Yet, amazingly, the AMY can be found at Le Manio as we will see later.

An important step in recovering megalithic science was when, in 2009, Robin Heath moved Howard Crowhurst’s theodolite sight to find the angular signature of his lunation triangle, relative to point Q. Moving the sight 14 degrees north of the southern kerb, he saw a stone which had been given a sharp edge suitable to start or end a day-inch count. But both Robin and I assumed three lunar years had been captured along the southern kerb as a day-inch count.

Figure 2 The Stone called R (left) from the NW and (right) looking to point P, the sun gate, along which three solar years were counted. (from FR Heath, 2009)

On reviewing our site plan, a simpler and more interesting location for the lunar count can be seen, which has far better evidence on the ground, firstly for the counting to all be within the open space provided by the quadrilateral and secondly, for having the lunar count between two stones with sharp edges.

Figure 3 Quadrilateral site plan of 2010 showing stone R and keystone K, two pointed stones apart by three lunar years in day-inches, indicated by the four-square rectangle which contains two (tessellating) lunation triangles.

A different take on the lunation triangle is given by a rectangle made of four squares (Fig. 3), in which two such triangles fit and whose diagonals represent the solar year and its longer sides, the lunar year – for the purpose of counting the same number of each of these years. The northern kerb has a small boat-shaped stone, here called K, whose sharp end touches the four-square rectangle’s northwest corner, permitting a lunar count to stone R.

Figure 4 Two views of stone K showing proposed count from stone R to its sharp edge

The symbolism of the solar year count was previously seen as running towards the summer solstice sunrise, from point P (the sun gate) to stone R, at an angle well-known to be near the angle of a 345 triangle at this latitude. But this new proposal suggests that both the solar and lunar counts should start at stone R, from where they jointly depart.

The end-stones of chambered dolmens were quite clearly intended, by their builders, to receive the light of a given horizon event of sun or moon. Thus the western jamb of the sun gate may have been conceived as an “end-stone”, which receives the sun’s light at sunrise – in both the summer and winter solstice. Similarly, one suspects that the newly-named stone K is the end of the moon count because the northern kerb is aligned to the northerly moonrise at the Moon’s minimum standstill.

This reverses the previously dominant directional assumption, perhaps cultural, of pointing towards an horizon event. The more direct idea, of the receiving of the light from the midsummer solstice sunrise or minimum moonrise, would probably have viewed the count’s direction as similar to the rays of celestial light on successive days.

These new proposals reveal an unobstructed and more-plausible region for day-inch counting to have been performed within the Quadrilateral.

As promised, the AMY was to be found within the 945 day-inch length to stone 32 which is also the duration of 32 lunar months. That length is also the length of 29 AMY but how did the megalithic come to know that? For the answer to that, we have to look towards a later post describing another skill they had, of numerical factorization.


Crowhurst, Howard. 2009
Le Site Mégalithique du Manio à Carnac.
available here.

Heath,Robin. 2009.
The Discovery Of A Soli-Lunar Calendar Device Within An Astronomical Ritual Complex At Le Manio, Morbihan, Brittany: The Discovery Of A Soli-Lunar Calendar Device Within An Astronomical Ritual Complex At Le Manio, Morbihan, Brittany,
available here.

Heath, Richard and Robin Heath. 2010.
The Origins of Megalithic Astronomy as Found at
Le Manio:

based on a Theodolite Survey of Le Manio,
Carnac, Brittany, 22-25 March 2010.
available here.

Heath, Richard. 2014.
2014: Sacred Number and the Lords of Time. Inner Traditions. Ch. 3.

You may also like to read the early chapters of Sacred Geometry: Language of the Angels (2020) for a fuller statement of how counting and measures defined an unexpected path towards a powerful type of average time astronomy.