New analysis says Stonehenge is a calendar to help people track through a solar year of 365.25 days.
Scientists have long believed that the ancient stone circle Stonehenge, perhaps the most famous ancient monument of its kind in the world, is actually – given its alignment with the solstices – a massive calendar.
But new research, published in the scientific journal Antiquity, has now revealed for the first time precisely how this aspect of the ancient stones works.
Recent discoveries about the stone circle’s history, combined with fresh evaluations of several other ancient calendar systems, persuaded Professor Timothy Darvill, from the University of Bournemouth in the United Kingdom, to look at Stonehenge with fresh eyes.
“The clear solstitial alignment of Stonehenge has prompted people to suggest that the site included some kind of calendar since the antiquarian William Stukeley,” says Prof. Darvill.
“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.”
Most importantly, recent research showed that Stonehenge’s huge stones, known as sarsens, were all added to the site during the same phase of construction, around 2500 BC.
They were sourced from the same area and subsequently remained in the same formation. This suggests they worked as a single unit.
Darvill evaluated these stones, analysing 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. Each of the 30 stones in the sarsen circle represents a day within a month, itself divided into three weeks each of 10 days,” says Professor Darvill, who also notes that distinctive stones in the circle mark the start of each week.
Moreover, an intercalary month of five days and a leap day every four years were needed to match the solar year. An intercalary period is a set time – usually a day or month – inserted into a calendar to harmonise it with the solar year.
“The intercalary month, probably dedicated to the deities of the site, is represented by the five Trilithons in the centre of the site,” says Professor Darvill, “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 BC and was adopted in Egypt as the Civil Calendar around 2700 and was widely used at the start of the Old Kingdom about 2600 BC,” says Professor Darvill.
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 wider cultural connections. The grave of the Amesbury Archer, a gravesite found close to Stonehenge is over 4000 years old.
The archer was 35–45 years old when he died and placed in a wooden chamber beneath a low mound. However, scientists have established that the archer was born in the European Alps and moved to Britain as a teenager.
Prof. Darvill says he hopes future research might shed light on these possibilities. Ancient DNA and archaeological artifacts may yet reveal connections between these cultures.
Nonetheless, the identification of a solar calendar at Stonehenge should change the way we perceive its’ functions in ancient society.
“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,” he says.
“A place where the timing of ceremonies and festivals was connected to the very fabric of the universe and celestial movements in the heavens.”