Le Menec: Start of Carnac’s Alignments

The Meaning Of Le Menec

“Alignments” are long rows of stones, that run in parallel for long distances through the landscape. The alignments in Carnac, Brittany, often have a starting point in what the French call a cromlech. Based upon a circular geometry, these monuments are made up of stones following arcs to form a single compound shape. The stones of a cromlech can be touching or they can be spaced out and in some cases, stones might have been removed during the historical period but in some cases also, gaps in the “walls” of a cromlech were probably intentional and are there on purpose.
Originally published July 2012

The alignment we will be considering here is called Le Menec. Its western end is defined by a cromlech since occupied by later buildings and some of the breaks in the cromlech’s walls enable access whilst also, a number of stones in some of these buildings were probably “harvested” from the cromlech or the alignments. Some stones may well have been employed where they stood, as foundations for the buildings of the hamlet of Le Menec. The cromlech provides visitors with a car park, where one can stand before the alignments, at their start. The initial stones are very large and impressive – reminding one of Britain’s largest monuments, in particular Avebury where the stones are similar in their shapes but only used within a very large circle and circles inside or “avenues” of just two “rows” wandering the local landscape in parallel.

Both Avebury and Le Menec’s circular cromlech employ 3-4-5 triangles in their geometrical design, and in general all the circular structures in Britain follow the same design rules and units of measure as those found in Brittany. For example, the Le Menec cromlech is an egg shape in which a circle has been extended to form a longer perimeter length, a technique first identified by Alexander Thom in his pioneering surveying work undertaken between 1934 and his death in 1985.

Figure 1 Thom’s detailed survey of the Le Menec cromlech and its interface with the start of the western alignments. Note the use of 3-4-5 triangles employing megalithic “rods” (2.5 megalithic yards) and a circle in which the triangles enable one half to be lengthened in perimeter. The rows also appear separated using megalithic yards though they significantly stray from forming a straight line. The azimuth Thom determined (18.383o) has turned out to symbolise what the alignments probably represent, the moon’s nodal year of 18.6 years through a solar year to eclipse year relationship to East.

Thom had found ‘families’ of geometrical design rules in British stone rings while undertaking the first accurate surveys of them, a hobby he developed before WW2. Thom found a unit employed in megalithic structures which he named a megalithic yard (MY), of about 2.72 feet in length (0.829m). Following the publication of his controversial Megalithic Sites in Britain (1967), the British archaeological fraternity challenged Thom, in 1970, to survey the largely uninvestigated Carnac Alignments as a test for the same or similar geometrical and metrological rules. The then editor of the journal Antiquity, Dr Glyn Daniel, oversaw the project which was also filmed by the BBC for a Chronicle documentary about Thom’s work [First broadcast 31 October 1970 and viewable at http://www.bbc.co.uk/archive/chronicle/8604.shtml]. Thom spent only 6-8 weeks in Carnac but achieved an astonishing amount including providing an accurate survey of the alignments and their cromlechs.

Le Menec’s cromlech (see figure 1) is a Type 1 Egg – perfectly in accord with Thom’s already developed morphology – a fact that can be determined in spite of the large gaps in its perimeter. There are many surveyed Type 1 eggs in Great Britain and Le Menec’s egg is laid out using the same megalithic yard length used in Britain to define its egg shaped rings. The alignments also employed this unit in their row separations, if not in the separations between stones within the rows, running eastwards.

Figure 2 The north-western quadrant is a wall or “kerb” that follows the circle upon which the cromlech’s geometry acted to generate a longer perimeter, nearly 82/72nds [1.138] of the circle’s circumference.

Interpretations of Le Menec

The interpretations of Le Menec largely comprise folklore stories that may relate somewhat to their original purpose. The name Le Menec apparently means “moving stones” in Breton and this name might well be relevant to the original purpose of this monument. For instance, the Moon is often clearly represented by megaliths, whilst the moon itself being a very large moving stone, and within the many monuments around Carnac, the battalions of stones appear to represent something actual such as the march of moon risings or settings on the eastern or western horizon.

The land of Brittany was settled by Welsh speakers between the 2nd and 4th century whilst before this the lands had been visited by the Romans, hence the idea that the alignments represented in some way a Roman Legion monumentalised. The romantic notions of the 19th century were excited by this hard-to-visit region of France, where dirt tracks restricted access, helping to preserve the many megalithic constructions that spread out for many kilometres in every direction. The interest of a few gentlemen antiquarian/ archaeologists led to some documentation of sites, even a photographic record and early cataloguing by Felix Gaillard, whose hotel still stands in Plouharnel and which now includes a megalithic museum with much of his only recently re-discovered work on display. Gaillard thought that some observations were possible from the cromlech and across the alignments, in particular that an anomalous, larger stone or menhir marked the sun at summer solstice sunrise. The menhir would today be called a foresight and the observer’s location the backsight, this possibly located behind the western kerb of the cromlech as in figure 3.

When Thom visited in 1970, nearly a century after Gaillard, he appears to have deviated from his usual procedure of checking for the four possible alignments to the solstice sun – otherwise he would have noted the prominent ‘table stone’ amongst the rows. Instead, he focussed on revealing the geometry of the cromlech as founded on the same megalithic yard and design that employed 3-4-5 triangles to enlarge the circle into an egg. He then began a statistical analysis of the alignments to test whether they too were originally laid out using megalithic yards and separated along the rows by whole numbers of megalithic “rods” of 2.5 MY or 6.8 feet. These megalithic rods figured in the diameter of the cromlech and sides of the triangles used to extend its perimeter into an egg.

Figure 3 By stretching a book illustration of Gaillard’s survey of Le Menec on the Google Earth view of the site, his survey makes some sense. However the chosen backsight was obscure and his sightline needed to be brought down to the ‘table stone’ so that it then passes through the centre of the cromlech’s forming circle[The survey, circa 1890, has a faulty compass and this was probably added later since it erodes the significant angle of the alignments to east and at odds with the survey’s correlation of angular realities and stones still found today.].

Thom left us the only complete survey of the alignments and of many other monuments at Carnac. He achieved a masterful but preliminary overview of the whole area around Carnac and the Bay of Qiberon but (because of a lack of time, failing eyesight and advancing years) he did not follow up on all the questions he otherwise would have. Amongst these lay the question :What was the intended function of the alignments and their relationship to the highly specific cromlech at their start?

In Britain, Thom had found lunar observatories to be associated with stone rows which, unlike Carnac’s alignments, were divergent and not parallel. Thom had identified that these enabled megalithic astronomers, at sites with different latitude, to take two observations of the moon on the horizon, on successive days, when approaching its extreme orbital azimuth, and from these alignments deduce a greater azimuth that would have occurred had the horizon caught the moonrise at the exact moment of extreme monthly azimuth. [This highlights the problem with horizon event astronomy and especially lunar observation where the moon moves more rapidly than the sun, per day, and horizon events are therefore unlikely to occur at the exact moment when the maximum lunar azimuth would occur. To work out an extreme that occurs between horizon observations one must extrapolate between those two observations. This was done by building a divergent “fan” of stone rows or a right angled triangle also using megaliths, from which the extreme horizon alignment which never actually occurred can be located accurately, as if it had occurred on the horizon.]

It was only using extrapolation that the azimuth for lunar maximum and minimum standstill could become established to the high levels of accuracy found between Carnac’s stones as backsights and distant foresights such as large menhirs visible on the horizon. This proposal for ancient technical competence evoked great resistance from the often technophobic archaeologists of Thom’s day. Also, and somewhat ironically, his discovery that stone rows could be used for extrapolation almost certainly prevented him recognising a simpler use of the western alignments of Le Menec as marking successive moonrises during the south to north portion of the moon’s orbit.

The alignments appear to have recorded the moon’s ecliptic latitude relative to sun’s path throughout half a lunar orbit during most of the 18.6 year cycle in which the moon’s orbital nodes complete a single circuit of the ecliptic, called a Nodal Year (see later). However, Thom could not have seen how the cromlech might function as a sidereal observatory required for the building of the western alignments – the task undertaken here and made possible through the discovery of its inch-counted metrological geometries.

To achieve their mastery of the moon in its orbit, the cromlech builders had to contemplate a new type of astronomy that indicated where the moon was on the ecliptic, then to deduce its deviation in latitude relative to the sun’s path, when seen on the horizon at rising. To do this the megalithic astronomers needed to know three things: the azimuth angle of a moonrise on the horizon, the location of the moon relative to the ecliptic, and where that part of the ecliptic rose (each day) on the horizon. Irregularities in where and when the moon rises can make its ecliptic latitude measurable (see figure 4 below).


Figure 4 Effect on the Time of Moonrise when the Moon’s orbit passes above or below the Ecliptic

NEXT: as Sidereal Observatory


This paper proposes that an unfamiliar type of circumpolar astronomy was practiced by the time Le Menec was built, around 4000 BCE.

  1. Abstract
  2. Start of Carnac’s Alignments
  3. as Sidereal Observatory
  4. using Circumpolar Marker Stars
  5. dividing the Circumpolar stars
  6. maintaining Sidereal Time in Daylight
  7. measuring the Moon’s Progress
  8. as Type 1 Egg
  9. transition from Le Manio
  10. the Octon of 4 Eclipse Years
  11. building of Western Alignments
  12. key lengths of Time on Earth