Alexander Thom was born on March 26, 1894, and died on November 7, 1985. He was a Scottish engineer known for developing a theory about the Megalithic yard, grouping stone circles, and conducting research on Stonehenge and other ancient sites.

Life and work

Alexander Thom was born in Carradale, Scotland, in 1894. His father, Archibald Thom, was a tenant farmer at Mains Farm, which belonged to Carradale House. His mother, Lily Stevenson Strang, was from the family of Robert Louis Stevenson. His father trained the church choir, and his mother played the piano.

Thom lived at Mains Farm during his early years before moving to The Hill Farm in Dunlop, Ayrshire. His father taught him the value of hard work, and Thom taught himself industrial engineering. In 1911, he entered college in Glasgow, where he studied with John Logie Baird. In 1912, he attended a summer school at Loch Eck, where he learned surveying and field astronomy from Dr. David Clark and Professor Moncur. In 1913, at the age of 19, he helped survey the Canadian Pacific Rail Network.

Thom graduated from the Royal College of Science and Technology and the University of Glasgow in 1914, earning a BSc with special distinction in engineering. He had a heart murmur and was not drafted into the First World War. Instead, he worked on civil engineering projects, including the Forth Bridge, and later designed flying boats for the Gosport Aircraft Company. In 1917, he married Jeanie Kirkwood, and they shared a long and lively marriage.

Thom returned to the University of Glasgow in 1922, where he worked as a lecturer until 1939. During this time, he earned a PhD and DSc. In 1922, he built a home called Thalassa and added a windmill to generate electricity. His father died in 1924, and Thom took over the farm, where he had three children: Archibald, Beryl, and Alan. He helped develop the Department of Aeronautics at the University of Glasgow and taught subjects like statistics, surveying, theodolite design, and astronomy. From 1930 to 1935, he was a Carnegie Teaching Fellow.

During the Second World War, Thom moved to Fleet in Hampshire, where he became Principal Scientific Officer at the Royal Aircraft Establishment. He led a team that developed the first high-speed wind tunnel. Later, he became a professor and chair of engineering science at Brasenose College, University of Oxford. There, he became interested in how prehistoric people built megalithic monuments, such as stone circles in the British Isles and France, and their connection to astronomy.

In 1955, Thom proposed the idea of the "megalithic yard," a standardized measurement used by prehistoric people. He retired from academia in 1961 to focus on this research. A building at the University of Oxford, housing the Department of Engineering Science, is named after him.

From around 1933 to 1977, Thom spent weekends and holidays with family or friends, using theodolites and surveying equipment to study over 500 megalithic sites. He classified stone circles into types such as Type A, Type B, Type D, and others. He suggested that some stone circles were built to predict eclipses using 19-year cycles and identified solar and stellar alignments at these sites.

Thom believed that prehistoric people used a solar calendar. He studied statistical data from 2100 to 1600 BCE and proposed a year divided into 16 months. He linked these months to modern Christian festivals like Whitsun and Lammas. He noted that prehistoric people may have used similar divisions but did not know how advanced their calendar was.

Thom expanded on these ideas in his later books. His final book, Stone Rows and Standing Stones, was written with his son Archie after they surveyed the Carnac stones from 1970 to 1974.

Thom’s theories were controversial among archaeologists but gained support in the 1960s counterculture movement. His work was linked to the idea of "the lost wisdom of the ancients" and sometimes associated with pseudoscience.

In 1975, his wife, Jeanie, died. In 1981, he had an eye operation, and in 1982, he broke his femur after falling on ice. He continued writing using a dictaphone and the help of an audio typist, Hilda Gustin. He moved in with his daughter Beryl in 1983 in Banavie. Registered as blind, he completed his final book, Stone Rows and Standing Stones, which was published in 1990 with the help of Aubrey Burl. Thom died on November 7, 1985, at Fort William Hospital, at the age of 91. He was buried near Ayr.

Alexander Thom is survived by his daughter, Beryl Austin, and his grandchildren. His son, Archie, lived after him but died in 1995 from a brain tumor.

BBC Chronicle – Cracking the Stone Age code

In 1970, Thom appeared on a BBC television documentary called Chronicle, hosted by Magnus Magnusson. The program included famous archaeologists such as Dr. Euan Mackie, Professor Richard J. C. Atkinson, Dr. A. H. A. Hogg, Professor Stuart Piggott, Dr. Jacquetta Hawkes, Dr. Humphrey Case, and Dr. Glyn Daniel. The show discussed the differences between traditional archaeology and Thom's new and different ideas. This was an important moment in Thom's career, as it allowed him to share his views on national television. Even though many people criticized his work, Thom did not express his frustration toward the archaeological community. As he said during the Chronicle program, "I just keep reporting what I find."

Later use of his work

Thom proposed a unit of measurement called the Megalithic yard, which some controversial books suggest is a part of the Earth's circumference based on a 366-degree geometry system. One such book is Civilization One: The World is Not as You Thought It Was, written by Christopher Knight and Alan Butler, who support the 366-degree geometry theory.

Clive Ruggles analyzed Thom's data using classical and Bayesian statistical methods and concluded that the evidence supporting the Megalithic yard is weak. He noted that even if the unit existed, the uncertainty in its exact value is several centimeters, much larger than the 1mm precision Thom claimed. Ruggles suggested that the measurements could have been made by pacing, with the "unit" reflecting an average step length. David George Kendall previously argued that pacing would likely cause more variation in measurements across different sites. After investigating for the Royal Academy, he concluded that the idea of a smooth, non-quantal distribution of circle diameters for Scottish, English, and Welsh true circles is unlikely.

Douglas Heggie also questioned Thom's theory, stating that his analysis found little evidence for a highly accurate unit and no strong reason to believe such a unit was used.

Euan MacKie, recognizing the need to test Thom's theories, excavated the Kintraw standing stone site in Argyllshire in 1970 and 1971. He discovered an artificial platform on the hill slope above the stone, which supported Thom's prediction about an observation platform. This finding led MacKie to test Thom's geometrical theories at the Cultoon stone circle in Islay, where he also found positive results. As a result, MacKie broadly accepted Thom's conclusions and published new prehistories of Britain. However, a later re-evaluation of Thom's fieldwork by Clive Ruggles argued that Thom's claims about high accuracy in astronomy were not fully supported by the evidence. Despite this, Thom's influence remains strong. In 1979, Krupp wrote that Thom "almost singlehandedly established the standards for archaeoastronomical fieldwork and interpretation," and his work continues to shape the practice of statistical testing in archaeoastronomy.

In his book Genes, Giants, Monsters and Men, Joseph P. Farrell wrote, "If Thom was right, the development of human civilization may have to be rewritten." Farrell suggested this is why Thom faces opposition from some groups.

In Rings of Stone: The Prehistoric Stone Circles of Britain and Ireland, Aubrey Burl referred to the megalithic yard as "a chimera, a grotesque statistical misconception."