Rewriting Alexander Thom's Megalithic Hypotheses

 Stone Circle Design and Measurement: Standard Units and Complex Geometries 


"No believer in the uniform megalithic yard seems at all keen to propose that Thom may have perceived the merest tip of the iceberg, and may also have misinterpreted what he saw."

The nature of beliefs in prehistoric Europe and the intellectuality and culture of its population have been viewed at various levels over time. Perception has ranged from their being barbaric and ignorant - the view of early antiquarians - to a modern perception of their having been creative and investigative - a view much influenced by the work of the late Alexander Thom, former professor of engineering at the University of Oxford. Thom's conclusions derive from statistical analysis of information gleaned from the many stone circles, stone rows, and associated features he so meticulously surveyed. Some of his ideas have found their way into archaeology, but not all that he preached has stood the test of close scrutiny over time.

Two aspects of Thom's work are considered:

1. Metrology

An investigation into the use of a uniform unit of measure in megalithic structures. The unit was postulated as being consistent over space and time, and universally applied within a broad cultural group throughout Britain, Ireland and Brittany, and potentially throughout Europe. Thom declared the common unit to be a Megalithic Yard of some 829mm (2.72 feet) divided into 40 Megalithic Inches. He also postulated a Megalithic Rod of two and a half megalithic yards for measurement on perimeters.

2. Geometry

Thom suggested that prehistoric stone rings were set out not only with a common unit of measure but also to certain geometrical principles, notably featuring Pythagorean, or near-Pythagorean, triangles (with sides of integer unit lengths.) In combination, Thom's suggested metrology attempted to overcome problems deriving from the incommensurability of pi and, again by implication, other irrationals related to the regular polygons.

Thom's statistical analysis has been repeated, checked and refined, and produces consistent results. Although not conclusive, the megalithic yard is primarily suggested by data relating to diameters at Scottish sites, and possibly Welsh. The megalithic fathom is hinted at for England, and the yard strongly indicated overall.

Thus, some of Thom's ideas have found their way into archaeology, but not all that he preached has stood the test of close scrutiny over time.


In my view, Thom's followers should not be repeating his liturgy ad nauseam, but should be recognising the weaknesses in his argument, and be addressing them. Perhaps, also, since archaeology recognises a hint of the megalithic yard in the data, archaeologists could, and really should, be doing this themselves - but the negative status of the lunatic fringe in archaeology's paradigm prevents this happening. Surely, it cannot be good practice for any academic discipline to erect such boundaries to free thinking. Indeed, can cognitive archaeology ever hope to succeed if certain ideas, themes and modes of thinking are rejected as being absurd from the outset, and therefore to be excluded from consideration?

If Thom's thesis fails to convince then, arguably, it must be either rejected or improved. However, while Thom's followers maintain that the argument cannot be bettered it will continue to lie dormant in archaeological circles. So, doing justice to Thom's work may well lie not in re-stating it, but in re-assessing and re-writing it, and trying again.

What is presented, then, is an attempt to demonstrate that there are equally arguable alternatives to the metrological themes in Thom's work. Beginning with a new perspective, the argument is built up leaning upon variations of Thom's hypothesis to result in a re-rendering of the proposition in a form that departs in many respects from Thom's thinking.
In any event, it can be shown that it is possible to argue Thom's thesis in a completely different way, and so Thom need not necessarily have been correct in all he claimed. The puzzle, then, is why so many people insist that he must have been.

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