Stonehenge has astronomical insights embedded in its architecture, and scholars have long debated how the site may have been used to keep time. Now, though, University of Bournemouth archaeologist Professor Timothy Darvill has proposed a new, archaeologically supported numerological interpretation that explains how the Neolithic monument may have functioned as a perpetual solar calendar.
Based on tropical years of approximately 365.25 days (the time it takes the Earth to complete one orbit of the Sun), solar calendars are used to track days, weeks, and months in line with seasonal cycles, making them particularly useful systems for regulating agrarian-based human routines. The calendar we use today, the Gregorian calendar, is one such example, but the earliest known systems date back several millennia.
At Stonehenge, Timothy highlights three components that could be regarded as the ‘building blocks’ of a Neolithic solar calendar. In a paper recently published in Antiquity (https://doi.org/10.15184/aqy.2022.5), he points to the Trilithon Horseshoe (five sarsen trilithons arranged in a ‘U’-shape), which sits at the centre of the Sarsen Circle (originally made up of 30 stones). Both of these elements are framed by the Station Stone Rectangle (comprising four smaller uprights, only two of which survive).
All three of these aspects are oriented north-east to south-west along Stonehenge’s principal astronomical axis, which is aligned on the summer and winter solstices. Crucially, archaeological analysis of the site’s development (see CA 275 and Darvill et al. Antiquity; https://doi.org/10.1017/S0003598X00048225) has shown they were all established during the same building phase (2620-2480 BC). Recent geochemical research, moreover, has found that most of the sarsen stones come from the same geographical area, in West Woods, a short distance to the north (CA 367 and Nash et al. Science Advances; https://doi.org/10.1126/sciadv.abc0133), lending further weight to the possibility that all three components were conceived of as a single unit.
Taking the solstitial alignment of these features as his cue, Timothy analysed the monument’s layout to look for calendrical clues. ‘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 ten days,’ he explained, noting that gaps between certain stones appear to split the circle into three sections. A 12-month solar calendar of this kind would have required a leap day every four years and an intercalary month of five days, ‘represented by the five Trilithons in the centre of the site’, Timothy said. ‘The four Station Stones outside the Sarsen Circle provide markers to notch-up until a leap day.’ This system would have seen the solstices framed annually by the same stone pairings.
As for where the system could have come from, Timothy acknowledges that it could have evolved locally. Solar calendars were not unique to Britain, however – similar ideas were also emerging in the eastern Mediterranean region, particularly in Egypt and Mesopotamia. ‘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 BC and widely used at the start of the Old Kingdom about 2600 BC,’ he said. It is possible, therefore, that these solar ideas could have arrived in Britain from further afield. ‘Such a source would be part of the widespread interest in solar cults across Europe and the Old World from the mid-3rd millennium onwards,’ Timothy said.