Could it be that the story of man, as commonly told, is based on a false premise? Archaeologists assume a smooth progression in human development from primitive hunter-gatherers to sophisticated city dwellers. But this cosy theory has been undermined by the work of a professor of engineering. Alexander Thom is credited with the discovery that structures left by late Stone Age man were built to a standard unit of measurement so precise that he could identify its original value to an accuracy less than the width of a human hair.

Thom died in 1985 without ever being able to explain the origin of what he called the “megalithic yard”. Our quest has led us to the answer; in the process we have opened a treasure chest of lost knowledge leading us to conclude that in prehistory there was a highly advanced intelligence at work.

It is an incontestable fact that on the western fringes of Europe, from parts of Scandinavia and the Baltic down to northern Spain and throughout the British Isles, an ancient people created huge circles and other structures using stones weighing up to 350 tonnes. The 20m (65ft) high Le Grand Menhir Brisé in Brittany is an example, while on the banks of the River Boyne in Ireland they left a massive circular structure now known as Newgrange, a thousand years older than the Great Pyramid in Egypt. How was it done?

Thom realised that prehistoric builders had a significant interest in astronomy, and that many of the larger sites have solar, lunar and stellar alignments. From the Ring of Brodgar in Orkney to Stonehenge in southern England and to the stone rows of Brittany, it was clear that these people spent a lot of time observing the movements of the heavens. Newgrange, for example, has a single shaft that was carefully constructed to allow the light of Venus to penetrate into a central chamber once every eight years, giving the engineers who designed the observatory a calendar so accurate that it can be beaten today only by the use of atomic clocks. Even more surprisingly, it appeared that most of these prehistoric sites, from the island off northern Scotland down to the coast of Brittany, had been constructed using a standard unit of measurement — Thom’s megalithic yard, equal to 82.96656cm.

Thom’s work is still largely ignored because it is inconsistent with scholarly opinion of the abilities of prehistoric man. Thom, who was professor of engineering at Oxford University from 1945 until 1961, could not explain his findings. He was aware that even if there had been a priesthood who cut poles to the required length and then passed them on over the tens of thousands of square miles involved and across many generations, such uncanny accuracy could not have been the result. The only hope of resolving the issue was to attempt to identify a methodology for reproducing such a length at different locations.

Our shortlist of possibilities for any naturally occurring unit of measure came down to just one candidate: the turning of the Earth on its axis which enabled early man to measure the passing of time. But how could a unit of time be converted into a linear unit? We eventually realised that the answer lay in pendulums.

At the heart of the traditional clock lies the pendulum. The wind-up spring or electrical motor is merely a mechanical device to provide a power source to keep the pendulum swinging rather than have it swing by hand. And the dial on the clock-face is simply a convention to give us a standardised means of reading off agreed units of time. When we stripped away the modern aspects of a mechanical clock we realised that it is, in essence, nothing more than a swinging pendulum.

We could imagine that a hypothetical prehistoric clock could work perfectly well without a clockwork mechanism or a dial. All we needed to create such a timepiece was for two of us to take turns to swing a pebble on the end of a piece of twine with our hands while the other counted off groups of completed beats. For example, a small stone could be put in a line for every hundred beats. This “man-clock” would work well enough to allow for accurate astronomical calculations to be carried out over several days if necessary.

Further research established to our satisfaction that our megalithic ancestors calibrated their pendulum by observing the planet Venus.When the experiment is undertaken in Orkney, where some of the most magnificent of the megalithic monuments are to be found, the size of the resulting pendulum is very significant. The pendulum proved to be half a megalithic yard, the full length of which deviated from Thom’s findings by a staggering one part in 2,700. Allowing for the human factor (that someone has to hold the pendulum and decide when to start and stop it), the Venus-based half-megalithic yard pendulum is perfect. Our result is within the very fine margin of error identified by Thom.

This method of reproducing the megalithic yard was so simple it was not necessary for the master mason to have the ability to count the number of beats in any modern sense. Counting does not have to be part of a tiered system such as the base ten method used today, in which we notch up in multiples of ten by adding a nought after the digit. A nursery rhyme or a sea shanty is a good way of counting out a set number while pointing at a sheep for each word will tell you whether your flock is still intact:

“Eeny, meeny, miney, mow, catch a monkey by the toe. If he squeals let him go. Eeny, meeny, miney, mow.”

It follows that measuring something as simple as this could be old as language itself. Indeed, the words “eeny, meeny, miney, mow” are thought to be an ancient British counting technique from more than 4,000 years ago.

Having established the method for “proving” the megalithic yard, we took another step forward and began to construct a theoretical weight and capacity system. We began at the point in history at which many more modern cultures appear to have started when creating such units; by making a cube with sides of an equal length and filling it with water. We knew that those creating the metric system had opted for a length of one tenth of a metre, which they cubed. The volume of water in such a 10 x 10 x 10cm cube was designated a litre, and the weight of such a body of water was named a kilogram.