The distinctive point
Megalithic yard (Thom hypothesis): a value with room for evidence
Thom’s proposed yard is a statistical reconstruction. The converter’s 0.829 m value lets the hypothesis be tested; a close fit alone cannot establish a shared prehistoric ruler.
Basis: statistical-hypothesis. Check the record source.
No same-system neighbour is modelled; the source and period carry the context.
A proposed prehistoric ruler
The megalithic yard is a modern statistical hypothesis about prehistoric Britain and Brittany, associated with Alexander Thom’s surveys. It is not an attested Druid standard. The converter uses a rounded 0.829 m so the hypothesis can be reproduced; the proposed prehistoric use remains disputed.12
The catalogue’s ±0.03 m allowance and low label are site conventions. They are not Thom’s reported estimation error, a construction tolerance, or a probability that the unit existed. Relevant local survey and critique papers are held; their claims still require exact source and model boundaries.
What the unit meant
Engineer Alexander Thom argued that British and Breton megalith builders used a common unit of about 2.72 feet or 0.829 m. His case came from statistical clustering in surveyed circle diameters rather than a marked rod, text, or inscription. The proposal became central to debates about prehistoric geometry, astronomy, and the organisation required to transmit a standard.
How this site models it
The converter includes Thom’s 0.829 m value so readers can reproduce the hypothesis against Stonehenge and other plans. It is labelled interpretive reconstruction, given low confidence, and assigned a broad plus or minus 0.03 m uncertainty. That treatment preserves the mathematical question without promoting the unit to measured historical fact.
What not to infer
Statistical evidence depends on sample selection and alternative models. Porteous argues that approximate pacing must be compared with the exact shared-unit hypothesis. A full regional reanalysis is outside this short conversion dossier. A match in megalithic yards is a result to investigate, not proof that builders carried one standard rod across prehistoric Britain.
Stonehenge: the case-study lens
The world’s best-known prehistoric stone circle combines strong solar geometry with the enduring and disputed claim that megalith builders shared a standard yard. This pairing is a historically bounded investigation, not a claim that one decimal unlocks the whole building.
Open the full Stonehenge dossier.
Values in the site matrix
| Standard | Representative | Site allowance | Region | Period | Confidence |
|---|---|---|---|---|---|
| Megalithic yard (Thom hypothesis) | 0.829 m | ±0.03 m | Britain and Brittany | Neolithic and Early Bronze Age hypothesis | low |
Sources and Further Reading
- Alexander Thom, Archibald Stevenson Thom and Alexander Strang Thom, Stonehenge, Journal for the History of Astronomy 5 (1974), pp. 78–83. Survey and attributed megalithic-yard/rod reconstruction. Article record.
- Hugh L. Porteous, Megalithic Yard or Megalithic Myth?, Journal for the History of Astronomy 4 (1973), pp. 22–24. Alternative pacing model and limits of exact-unit inference. Article record.