Standard unit of measurement used by Neolithic British monument builders and discovered by Alexander Thom. Thom, a former professor of engineering and science at Oxford University, derived the megalithic yard during the 1960s from his studies of megalithic monuments. After surveying more than 600 different megaliths, Thom came to two conclusions: that the megalithic sites were all used as astronomic observatories, and that they were all based on a standard unit, which he labeled a megalithic yard. The megalithic yard measures about 2.72 feet, almost exactly as long as the traditional Spanish vara, or rod. Thom suggested that the rod was passed down from the original builders of the megaliths and has survived to the present day.
Thom’s theory of the unit of the megalithic yard also helps explain the shapes of some of the stone rings of the British Islands. Thom showed that the builders actually erected the stones in noncircular shapes ellipses or ovoids to avoid complex fractions in the diameters and circumferences of their rings. Some of Thom’s theories are not universally accepted, but the megalithic yard is so pervasive that most scholars accept it as evidence that the monument builders of Stone Age Britain shared a com¬ mon culture. Thom’s ideas have also sparked a reevaluation of megalithic sites in Europe and Britain. If Thom’s conclusions are correct, they imply that ancient Europeans had a sophisticated geometry long before the cultures traditionally credited with developing mathematics. Some theorists even suggest that classical mathematics and the theory of number derive directly from the work of the ancient monument builders.