An archaeologist proposes that the monument is “a simple and elegant perpetual calendar” in a new study.

With its ancient origins and enchanting presence, Stonehenge is easily among the most iconic monuments in the world. The structure’s reputation as a cultural heritage site and a major tourist attraction is only heightened by the mystery of what these giant stones meant to the people who erected them on the plains of Wiltshire, England, some 4,500 years ago.

Now, a prominent researcher believes he has solved this long-standing riddle at last in new research that lays out exactly how Stonehenge likely worked. Timothy Darvill, professor of archaeology at Bournemouth University, suggests that Stonehenge is “a simple and elegant perpetual calendar based on the 365.25 solar days in a mean tropical year,” according to a research article published in the journal Antiquity on Tuesday. 

This calendar included self-correcting mechanisms to ensure accurate timekeeping over the course of years and was used to mark seasonal celebrations and rituals thousands of years ago—qualities that hint at the sophisticated cosmologies of the people who constructed Stonehenge, and their potential connections to societies hundreds of miles away.

“I think the communities that built Stonehenge not only had an incredible sense of quality in terms of the actual structure (Stonehenge is unique in its design and construction) but also a clear sense of purpose in making a place where people could come together for key festivals and ceremonies,” Darvill said in an email. “As I say in the paper, one of these is likely to be around healing ceremonies that depend on being in the right place at the right time.”

Darvill is far from the first expert to suggest that Stonehenge is a calendar; as he notes in his article, this interpretation has been around for centuries because it is clear that the monument is intentionally oriented to frame the summer and winter solstices within its characteristic arches. However, the new model incorporates recent archaeological breakthroughs from Stonehenge into a comprehensive framework that explains the position of these megalithic puzzle pieces.

“In the past people tried to make a calendar based on lunar months, but they were never able to actually make it work,” Darvill noted. “Here we have a real working model.”

For more than a decade, Darvill and his colleagues have been excavating hidden layers of Stonehenge and analyzing their findings. Recently, they deciphered the geochemical signatures of the monument’s sarsens, which are the building blocks of an outer ring called the Sarsen Circle, four stones beyond the ring called the Station Stone Rectangle, and five “Trilithon” stones at the center of the site called the Trilithon Horseshoe.  

While smaller bluestones within the monument had previously been traced to Wales, Darvill’s team discovered that all the sarsens were likely sourced from West Woods, a location about 10 miles north of Stonehenge, according to a 2020 study in Science Advances. Given this common origin, the sarsens were likely considered parts of a unified group by Stonehenge’s creators, which got Darvill thinking about his new calendar model.

“It was recognizing the unity of the sarsen settings” that inspired the research, he said. “That came from two sources. First, the dating models that we published a few years ago, but second, much more recent, was that just about all the sarsens seem to have come from a single source at West Woods near Marlborough.” 

“In sum, stones from a single source put up at the same time suggests a high level of integrity to what was being built,” he added.

Darvill pored over other calendars from the period while also examining the numerology and layout of Stonehenge’s megaliths. In the calendar that emerged from his analysis, each of the 30 megaliths in the Sarsen Circle represents a day of the month, which is itself divided into three 10-day weeks that are marked by anomalous stones. 

The Trilithons arranged at the center of the site acted as a special five-day “intercalary” month that shored up the drift of time over a single year, while the Station Stones marked leap days that were invoked every four years, similar to corrections in our own modern calendar. All of these calendric innovations worked together to ensure that the winter and summer solstices would be perfectly framed within its stone arches each year, denoting the correct passage of time.

The model not only fits into the structure of Stonehenge, it also echoes some of the solar calendars in use in parts of Europe and the Middle East some 5,000 years ago. Darvill suggests that Stonehenge’s creators may have been influenced by solar calendars developed in Egypt or Mesopotamia, an indication that farflung cultural exchanges were taking place. This possibility is supported by other archeological evidence at Stonehenge, including the bones of a man known as the Amesbury archer, who lived 4,300 years ago and originally hailed from the Alps, according to an isotope analysis of his remains. These findings hint that Stonehenge attracted people from great distances in the past as well as in the present, a draw that adds to its allure and inspires researchers like Darvill to unravel its secrets.

“Stonehenge is a wonderful challenge to everyone and it is enchanting and quizzical in equal measure,” Darvill said. “Starting to understand its many facets certainly gives a sense of responsibility, indeed the work we did excavating inside the circles in 2008 was very great responsibility and was the start of the research process that is now delivering new insights.” 

“I think there is a lot more still to know about the site,” he continued. “We have to recognize that it was long-lived and changed its use and purpose over time. Breaking it down into component parts is rather like analyzing the architecture of great churches or cathedrals or temples. They do not serve one purpose but many. So too Stonehenge. The calendar is important because it serves to unite those purposes in time.”

To that end, Darvill’s new calendar model opens a tantalizing window into the lives of people at Stonehenge, though he emphasized that his work on this hypothesis—and others—is just beginning.

“There is a lot more still to do!” he said. “We are still working on materials that we excavated in 2008 and there will no doubt be further insights as we pull all the various strands of evidence together. “

“And it's an exciting time in archaeology generally because so much rich material is coming to light as excavations prompted by development projects across the country enrich what we know and take us into places that had simply not been investigated before,” Darvill concluded.