Alexander Thom and the Megalithic Yard

Professor Alexander Thom was a man who spent several decades studying stone circles across the country in an attempt to decipher their meaning.

He discovered that not all were perfect circles - some were egg-shaped others elliptical - but whatever the shape they all seemed to show remarkable geometric precision long before the Age of Pythagoras.

Thom's conclusions were that the stone rings were astronomical observatories, a theory that, at the time, was met with some contempt. Even today his theories are not entirely accepted although it is now more or less agreed that most of our megaliths had some astronomical function - the level of complexity is still hotly debated.

As early as 1934, Thom had become interested in prehistoric stone circles and their astronomical associations, thereafter carrying out an ambitious project in which he accurately surveyed and carefully measured a number of megalithic sites throughout Britain.

Professor Thom published his megalithic findings in 1955 in the Journal of the Royal Statistical Society and after his retirement, published a further two articles that addressed a unit of measurement he found employed consistently at many prehistoric megalithic sites across Britain.

Thom's discovery was what he termed "the megalithic yard" - a measurement of 2.72 feet, or 0.83 metres - that suggests the megalithic builders of these stone circles had an advanced understanding of geometry and mathematics as well as astronomy.

Expanding on the ideas of Professor Thom is another controversial scholar, Dr Robert Lomas, co-author of Uriel's Machine - The Prehistoric Technology that Survived the Flood.

Dr Lomas is of the opinion that the Megalithic Yard - or rather the Megalithic Half-Yard, a measurement he favours - was developed in Orkney before spreading southwards through a trading network used by the ancient Orcadians.