Scholars have long seen in the monumental composition of Stonehenge evidence for prehistoric time-reckoning — a Neolithic calendar. Exactly how such a calendar functioned, however, is unclear. In a new paper, Bournemouth University Professor Timothy Darvill argues that the numerology of Stonehenge’s sarsen elements materializes a perpetual calendar based on a tropical solar year of 365.25 days.
The ensemble of sarsen structures at Stonehenge is unique in north-western Europe.
In terms of its design and construction, Stonehenge resembles no other stone monument of the mid-3rd millennium BCE.
Located on the chalk downlands of southern Britain, Stonehenge has long been thought to incorporate some kind of calendar, although its specific purpose and exactly how it worked remain far from clear.
At the beginning of the 20th century, scholars proposed that the monument represented a ‘May Calendar’ based on ‘clock-stars.’
Later, they advanced its interpretation as a ‘Neolithic computer,’ aligned to eight extreme positions of the Sun and the Moon, for the purposes of time-reckoning and predicting eclipses.
Some scientists, meanwhile, favored a calendar of 16 months, using the solstices, equinoxes, May/Lammas and Martinmas/Candlemas as turning points in the cycle.
These and many other interpretations, however, are all unsatisfactory, as they often use non-contemporaneous elements of the monument, reference astronomical alignments that do not withstand close scrutiny, or perpetuate the discredited idea of a ‘Celtic Calendar.’
“The clear solstitial alignment of Stonehenge has prompted people to suggest that the site included some kind of calendar since the antiquarian William Stukeley,” said Professor Darvill, a researcher in the Department of Archaeology and Anthropology at Bournemouth University.
“Now, discoveries brought the issue into sharper focus and indicate the site was a calendar based on a tropical solar year of 365.25 days.”
Crucially, recent research had shown that Stonehenge’s sarsens were added during the same phase of construction around 2500 BCE.
They were sourced from the same area and subsequently remained in the same formation. This indicates they worked as a single unit.
As such, Professor Darvill analyzed these stones, examining their numerology and comparing them to other known calendars from this period.
He identified a solar calendar in their layout, suggesting they served as a physical representation of the year that helped the ancient inhabitants of Wiltshire keep track of the days, weeks, and months.
“The proposed calendar works in a very straightforward way,” Professor Darvill said.
“Each of the 30 stones in the sarsen circle represents a day within a month, itself divided into three weeks each of 10 days. Distinctive stones in the circle mark the start of each week.”
“Additionally, an intercalary month of five days and a leap day every four years were needed to match the solar year.”
“The intercalary month, probably dedicated to the deities of the site, is represented by the five trilithons in the center of the site. The four Station Stones outside the Sarsen Circle provide markers to notch-up until a leap day.”
As such, the winter and summer solstices would be framed by the same pairs of stones every year.
One of the trilithons also frames the winter solstice, indicating it may have been the new year.
This solstitial alignment also helps calibrate the calendar — any errors in counting the days would be easily detectable as the Sun would be in the wrong place on the solstices.
Such a calendar, with 10 day weeks and extra months, may seem unusual today. However, calendars like this were adopted by many cultures during this period.
“Such a solar calendar was developed in the eastern Mediterranean in the centuries after 3000 BCE and was adopted in Egypt as the Civil Calendar around 2700 and was widely used at the start of the Old Kingdom about 2600 BCE,” Professor Darvill said.
This raises the possibility that the calendar tracked by Stonehenge may stem from the influence of one of these other cultures.
Nearby finds hint at such cultural connections — the nearby Amesbury archer, buried nearby around the same period, was born in the Alps and moved to Britain as a teenager.
“Finding a solar calendar represented in the architecture of Stonehenge opens up a whole new way of seeing the monument as a place for the living,” Professor Darvill said.
“A place where the timing of ceremonies and festivals was connected to the very fabric of the Universe and celestial movements in the heavens.”
The paper was published in the journal Antiquity.
Timothy Darvill et al. Keeping time at Stonehenge. Antiquity, published online March 2, 2022; doi: 10.15184/aqy.2022.5