The 1960s Theory That Made Stonehenge a ‘Prehistoric Computer’
For centuries, Stonehenge has been the source of competing theories about why it was built. The monument has been interpreted as a ceremonial site, a place associated with the dead, and later a building with important astronomical alignments.
In the 1960s the astronomer Gerald Hawkins proposed one of the most ambitious explanations yet. Stonehenge, he argued, might have been designed to track the movements of the sun and moon and could have helped its builders to predict eclipses.
Hawkins, a British-born astronomer and Boston University professor, developed the theory with the help of an early IBM computer. His findings formed the basis of his book Stonehenge Decoded, published in 1965, which brought the idea of Stonehenge as a sort of prehistoric astronomical machine to a wide audience.
But the theory was almost immediately controversial. Archaeologists challenged Hawkins’ statistical methods and questioned whether the features of the monument could have been used in the sophisticated way he suggested.
From Stonehenge to IBM computers
Hawkins’ interest in Stonehenge began with its connection to the sky.
During a visit in 1961 he became interested in the way the stones of the monument appeared to frame points on the horizon. He went back to the States with plans that showed locations of stones, holes and other features and started checking possible astronomical alignments.
The calculations were done on an early IBM computer at the Harvard-Smithsonian Observatory. Hawkins used the machine to investigate how the monument’s alignments would have matched up with the positions of the Sun and Moon in the time of Stonehenge’s construction.
He argued that several features seemed to be in accord with significant positions of the sun and moon.
The solar connection was not especially new. For centuries it had been known that Stonehenge aligned with the midsummer sunrise. More controversial was the claim of Hawkins that the monument also encoded information about the Moon.
The Enigma of the 56 Aubrey Holes
Hawkins’s theory focused on 56 pits that ran around the edge of the original Stonehenge enclosure.
These are the Aubrey Holes, named after 17th-century antiquary John Aubrey. Some of the pits have been excavated to reveal that they were used for cremation burials, but the original purpose of the pits remains a matter of debate.
Hawkins claimed that 56 was important because it could be used as part of a system to track the lunar cycles.
He suggested moving markers from one hole to another to monitor the Moon’s motion and predict when eclipses might occur. This resulted in the description of Stonehenge as a kind of “computer”—not a machine in the contemporary electronic sense but a physical system for tracking astronomical cycles.
It was an arresting idea, but it was never established as the purpose of the monument.
Why did the archaeologists object?
One of the most prominent critics of Hawkins was Richard Atkinson, one of the leading archaeologists who had excavated Stonehenge.
Atkinson, reviewing Stonehenge Decoded in 1966, argued that Hawkins had found too many possible significant alignments and had not proved that the results could not be due to chance.
He also questioned the practical foundation of the theory of eclipse prediction. There are no written records or numerical notations left by the builders of Stonehenge to show they had preserved the kind of long-term astronomical calculations that Hawkins’ model demanded.
Atkinson did accept that Stonehenge had astronomical significance, especially its orientation to the midsummer sunrise. What he objected to was the notion that the alignments were evidence of a sophisticated eclipse-prediction system.
The argument went on. For example, a paper in Nature in 1967 asked if the 56 Aubrey Holes were necessarily associated with eclipse prediction and suggested that, if the builders did predict eclipses, simpler methods might have been possible.
Later other researchers suggested other interpretations of the astronomical features and the Aubrey Holes of the monument. For instance, a 1972 article in Nature proposed that the holes, if they were counters at all, might have indicated periods of 56 months instead of 56 years.
What's left of Hawkins' idea?
Hawkins’ most spectacular claim – that Stonehenge was a device for predicting eclipses – should not be presented as an established archaeological conclusion.
There is strong evidence that Stonehenge had a significant relationship with the Sun. Its main astronomical alignment is one of the monument’s best-known features, and current research is investigating prehistoric people’s knowledge of the sky and the function of celestial observations in monumental architecture.
But the particular claim that the 56 Aubrey Holes amounted to an eclipse-predicting computer is unproven.
The holes themselves cannot be treated simply as astronomical counters either. Archaeological investigation has revealed cremation burials associated with them, adding another important dimension to the possible function of the monument. English Heritage says there is still debate over the original purpose of the holes, including whether some may have once held timber posts or stones.
However, Hawkins' work did alter the public discourse about Stonehenge. He used an early computer to test archaeological and astronomical patterns, which was unusual for its time, and Stonehenge Decoded helped popularise archaeoastronomy.
The notion of the 'prehistoric computer' continues to have appeal more than six decades on. But the evidence points to a more complex picture: Stonehenge is clearly aligned to astronomical phenomena, but how exactly the prehistoric communities understood and exploited those alignments is still up for debate.
