The Megalithic Yard: An Alternative Derivation

 Stone Circle Design and Measurement: Standard Units and Complex Geometries 


The book presents, in a somewhat different manner, the case for a higher intellectuality in the megalithic builders of Britain and Ireland than archaeology declares to be so.

The work seeks to demonstrate that the Megalithic Yard can be deduced quite independently of Thom and statistical analysis, as explained below.


At the heart of the argument is the suggestion that the megalith builders may have employed two units of measure linked by pi - a diametric unit (a diametron) and a perimetric unit (a perimetron). So, 22 diametric units would equal seven perimetric units. This would effectively overcome the problem of the incommensurability of pi - and would imply that the distance between orthostats may have been measured by the builders (and thus might be measured by us if we knew the size of the unit).

Given this bi-metric hypothesis, it would follow that had the builders used the same units at the Sarsen Circle and the Aubrey Ring at Stonehenge then it might be possible to identify their lengths - because the gaps between the sarsens and between the Aubrey holes would be an integer number of the same unit.

It would then be possible to check whether the derived unit is present at other sites with regularly spaced orthostats. The same units do, in fact, appear to be present at Machrie Moor V (8 stones), Cullerlie (8), Stennes (12), Lairdmannoch (10) and Grey Wethers (30). These sites range from southwest England to the north of Scotland.


The logic is as follows: the Aubrey Ring, at the south of England (with a circumference that would be a multiple of 56 units), has a diameter of 87m., and the inner ring at Machrie Moor V, at the west of Scotland (with a circumference a multiple of 8 units), has a diameter of 11.6m. As there would be the same number of units on the diameter as on the perimeter, it follows that 1/56th the diameter of the Aubrey Ring (1.55m) is an integer number of diametrons, and 1/8th the diameter of Machrie Moor V Inner (1.45m) is an integral multiple of the same unit.

By calculation, 87m/56 and 11.6m/8 have a connecting ratio of 15:14. Thus, the unit apparently common to both diameters is 103.6mm, which is one-eighth of a megalithic yard, being also the unit found to be common to cup-and-ring motifs (Davis, 1988). However, the unit found to be common to the diameters of all the regularly-spaced stone circles mentioned above is one-sixteenth of a megalithic yard (51.8mm) with a perimetric unit of 162.8mm. So, there would appear to be 1680 units at the Aubrey Ring, and 224 units at Machrie Moor V Inner.

Given that this unit is likely also to be present upon the outer ring at Machrie Moor V (which is 18.1m, or 352 units), the ratio between the two diameters is found to be 7:11, and the gaps between the orthostats prove to be multiples of one of these two values.

It may also be appreciated that the height of the panel on trilithon 57 at Stonehenge (Crawford, 1954), at 1143mm, is 22 diametric units, and, therefore, also 7 perimetric units. Applying this unit to other stone circles further betrays the 22/7, 11/7, or 14/11 relationship. Note Cullerlie, with its seven rings of 11 stones on an inner ellipse. The same units and the 22/7 ratio also appear to be present at Grange B, Lough Gur, County Limerick, Eire (diameter 45.6m, or 55 megalithic yards). So, the derived unit may well be present across the whole of Britain and Ireland - effectively considered preposterous by archaeologists.

Problems and Pointers

The problem of analysis with small units is discussed in the book, as is the variance in the units as found across the UK and Ireland. Thus, the diameter of Seahenge (Holme I), Norfolk, at the east of England, is suggested as being 112 units (with 56 timbers averaging two units each on the originating circle), being seven megalithic yards of 839mm, this being the length of a charred and apparently coppiced pole found set (presumably vertically) between two timbers in the southwest quadrant (Brennand and Taylor, 2003).

Thus, archaeologists may well have a megalithic yard in their possession that they typically refuse to recognise as such because they have declared that this particular measure does not exist as a uniform unit in megalithic ritual architecture, declaring such fancies to be typical of the 'lunatic' fringe.

Brennand, Mark and Taylor, Maisie (2003) 'The Survey and Excavation of a Bronze Age Timber Circle at Holme-next-the-Sea, Norfolk (1998-1999)'. Proceedings of the Prehistoric Society 69, 1-84
Crawford, O.G.S (1954) 'The Symbols carved at Stonehenge', Antiquity 28, 25-31
Davis, Alan (1988) 'The Metrology of Cup-and-Ring Carvings'. In Ruggles C.L.N (ed.) 392-422 (Records in Stone.)

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