The Megalithic Yard is a controversial unit of measurement originally proposed by Alex Thom following a study of hundreds of megalithic sites in Britain and Brittany. Very many attempts have been made to verify his conclusions but to no avail. Wikipedia(d) offers an interesting overview of the wide-ranging theories that the controversy has thrown up.
Humans have used their body parts as measuring tools right up to the present day, e.g. foot, finger or hand, so it was not surprising that the human pace provided a unit of measurement which has been suggested by many as the original megalithic ‘yard’.
>Paul Screeton in his Quicksilver Heritage [1882.48] noted that “the first person to write on prehistoric standard distances was Edward Milles Nelson (1851-1938).” He concluded that the megalith builders used a unit of measurement of 12.96 inches.<
Not unexpectedly, some researchers, such as Ulf Erlingsson(a), Sylvain Tristan(b) and Jim Allen(c) have endeavoured to link the megalithic yard with their interpretation of Plato’s Atlantis, sometimes using convoluted associations with ancient Egyptian and/or Sumerian metrics!
There is also an ancient unit of measurement known as the ‘long foot’ of 12.7 inches (32.2 cm). In early 2019, archaeologists from the University of Manchester and University College London concluded, after a study of three small carved chalk ‘drums’, that they “could be ancient replicas of measuring devices used for laying out prehistoric monuments like Stonehenge.” They found that “a string wound 10 times around the smallest of the drums would give a measure of exactly 10 long feet — a length used to lay out several ancient henge monuments“(e).
Douglas C. Heggie , an astronomer and mathematician as well as the late Aubrey Burl (1926-2020) , arguably the leading authority on British stone circles, have both expressed the view that Thom’s evidence was at best ‘marginal’.(f)