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Darvill’s Stonehenge solar calendar theory is fascinating and the author of this article put it to the test!		Source: Author provided

Putting Darvill’s Stonehenge Solar Calendar Theory To the Test!

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When an academic heavyweight with the credentials of a professor of archaeology proposes a new theory about Stonehenge, the media takes immediate notice. Such is the current excitement raised by Timothy Darvill, a professor at Bournemouth University, England, who argues that the numerology associated with the number of sarsen stones at Stonehenge equates to a perpetual calendar based on a tropical solar year of 365.25 days (Darvill 2022). Darvill’s Stonehenge solar calendar theory is compelling and, if true, will change how we view the Neolithic Stonehenge builder’s sense of time . . .

At first sight, Darvill’s Stonehenge solar calendar theory paints an incredible picture of the British Neolithic preliterate communities who built the monument. That they were capable of accurately determining the precise number of whole and quarter days in a year, more than two thousand years before the Greek scientist Hipparchus (190-120 BC), is indeed remarkable.

Certainly, Darvill is an undeniable expert on Stonehenge but is he taking a step too far with this hypothesis? Perhaps by focusing on numerology, which, has been, at best, traditionally left to the “lunatic fringes of archaeology,” Darvill has set himself up for serious resistance.

In this article I present a critical assessment of his recent proposal. To do so, I will assess his idea in two ways, firstly, in the context of British archaeology and, secondly, I will approach his hypothesis using an analysis based upon my own experimental methods.

Regular readers of Ancient Origins will recall that I am an experimental archaeologist who reconstructs the designs of Neolithic architecture using rudimentary methods of design, methods which I believe the prehistoric communities could perform. So, is it possible to create a sophisticated calendar by a preliterate culture whose intellectual capabilities were at a level we (today) would call primitive?

Before starting my analysis, I should point out that the idea equating the number of orthostats at Stonehenge to function as a celestial calendar is nothing new. The architect, John Wood, was one of the first researchers to suggest such an idea in 1740, closely followed by John Smith in 1771. Then, once the idea had taken hold, further proposals emerged, such as Geoffrey Higgins’ theory in 1829. And, as we enter the current period, Peter Newham extended the theory in 1972, as well as the topic recently being discussed in Ancient Origins by Stephen Childs (2021).

And now in 2022 we have the latest theory to consider and test: Darvill’s Stonehenge solar calendar theory.

Bournemouth University’s Professor Timothy Darvill’s Stonehenge solar calendar graph from his 2022 publication of his theory and its connections to numerology. (Bournemouth University)

Bournemouth University’s Professor Timothy Darvill’s Stonehenge solar calendar graph from his 2022 publication of his theory and its connections to numerology. (Bournemouth University)

Darvill’s Stonehenge Solar Calendar in Context

It appears to me that one significant drawback to Darvill’s Stonehenge solar calendar is the archaeological context in which his calendar operated, circa 2500 BC. At first glance I can think of at least five caveats.

Firstly, we have no appreciation of the intellectual capabilities held by preliterate Neolithic communities regarding their levels of numeracy. Certainly, there is no archaeological evidence to support that any form of numeracy was in use at all during the Late Neolithic, especially the time-period when Darvill’s calendar became operational (circa 2500 BC).

Of course, Stonehenge itself is the result of expert planning, design, and measurement. However, I have described elsewhere how it could have been built by people using a rudimentary form of mathematics based upon finger reckoning (Hill 2009).

But for Darvill’s calendar to work the Neolithic people would have had to possess sophisticated levels of mathematical ability to manage the substantial volume of data generated by his calendar (discussed further below). Certainly, such a calendar could not have functioned by people simply counting with their fingers.

Secondly, Darvill offers no suggestions (beyond a calendar) as to what other functions Stonehenge may have served. Certainly, his proposal that Stonehenge functioned as a calendar contradicts a more widely accepted explanation for Stonehenge as being a monument built to venerate the ancestors, as proposed by Professor Mike Parker Pearson. And of course, we must be open to the prospect that Stonehenge could have been built for reasons other than a calendar or a memorial to the ancestors.

Thirdly, Darvill declares that the British Neolithic communities were observing a solar calendar only, any lunar or solar-lunar calendars are ignored. Again, we have no physical archaeological evidence to support the claim that there were any forms of solar, lunar or solar-lunar calendars in operation (at all) during the British Neolithic. However, even if they did exist, then I do find Darvill’s omission of lunar astronomy difficult to ignore or omit from any calendar-observing system. More so, because it is widely accepted that the Neolithic people were watching both the Sun and Moon at their stone circles. For instance, the 156 Recumbent Stone Circles of Aberdeenshire were not only contemporary with the appearance of Darvill’s Stonehenge calendar, but these circles are recognized for having direct, observational associations with the midsummer full moon. Indeed, in a recent Ancient Origins article, I have demonstrated how a Neolithic solar-lunar calendar (based solely upon positional astronomy) could have easily operated from these circles (and without counting any days).

Fourthly, to make Darvill’s calendar work he has carefully selected only those features at Stonehenge which comfortably fit his hypothesis. He uses three particular sarsen stones features: the Trilithons (a word which originates from the Greek trilithos meaning three stones) hence there were five sets of trilithons (each set consisting of two uprights and a lintel); the Sarsen Circle (which consisted of 30 upright stones plus their lintels) and the Station Stones Rectangle (which consisted of four standing stones). All three features were raised at Stonehenge during the period 2620-2480 BC. Of course, I do not have a problem with the timings for when these three features were erected at Stonehenge, but Darvill has failed to mention a few other stone features that were also raised at Stonehenge during this same period.

For instance, there is no mention of the sarsen Slaughter Stone (and its two missing companion stones); the central Altar Stone is ignored; as, indeed, are the north-eastern double concentric arc of bluestones as well as the corresponding south-western single arc of bluestones (both arcs known now only by their stone holes i.e., the “Q and R holes”) and these arcs were positioned between the Sarsen Circle and the Trilithons (see Figures 1 & 2). Why ignore these features when they would have been “in the way” of those people who were trying to operate the Stonehenge calendar?

Figure 1. The location of the Q and R stone holes at Stonehenge. (Author provided)

Figure 1. The location of the Q and R stone holes at Stonehenge. (Author provided)

Fifthly, Stonehenge is a unique Neolithic structure. There is no other prehistoric monument like it throughout the British Isles (or Europe). My concern about Darvill’s hypothesis is that if Stonehenge was built purely to function as a time-keeping device then why does it stand alone? Its architecture is not repeated at any of the hundreds of other contemporary British stone circles. My issue here is how did the people maintain their “calendar-time” when they left the locality of the site of Stonehenge. Certainly, there is good archaeological evidence to show that the Neolithic people were visiting Stonehenge from many distant regions of the British Isles, but if you were living in, say, Neolithic North-east Scotland, how would you know what the exact day of the week, month or year it was without having to travel hundreds of miles south to check the date at Stonehenge?

Testing the Calendar

Before testing Darvill’s hypothesis, we will need to build the array upon which the Stonehenge calendar will work. Unfortunately, Darvill does not discuss at all how the sarsen stone features were designed, planned, set out and then raised in the manner where they are at Stonehenge. It is taken as a given that the people somehow managed to build Stonehenge without planning or design. Now, I ask the reader to consider this fact because it implies that before the Stonehenge Calendar was built, somebody had to possess all of this “calendar-knowledge in their head.” That is, that someone had to understand how the physical design of Stonehenge could correspond with the various temporal time periods it could record (i.e., past, present and future), and then that someone had to project all that “technical vision” into physical, architectural form. I do have to ask; how was this achieved with recourse to pen and paper?

An aerial view of Stonehenge on a sunny day in summer suggests it’s a calendar but is it a Stonehenge solar calendar? (anitalvdb / Adobe Stock)

An aerial view of Stonehenge on a sunny day in summer suggests it’s a calendar but is it a Stonehenge solar calendar? (anitalvdb / Adobe Stock)

Making it work

It looks to me that Darvill’s calendar could operate across three temporal “modes”:

  1. Acting as a time-keeping array: recording each successive day, daily.
  2. Acting as a time-planning array: being used to schedule future events.
  3. Acting as a time-recording array: being used to remember past events.

The operation of each temporal mode does indeed have their own difficulties but let us consider the simplest mode, an array for timekeeping. Darvill’s array is based upon using 30 sarsen stones to record the days of a month; five sets of Trilithons to record his additional 5 days (or epagomenal days); and using the four station stones so that a sixth day can be added to his epagomenal days every four years. However, before I set the “wheels of time” in motion and get the calendar working I need to address another factor which Darvill has not covered in his article. That is, how were the days of the calendar recorded?

In the absence of a solution offered by the Professor, I will have to assume that counters (of some description) were rotated from one stone to another, then moved around the calendar-array, as a method of recording the accumulation of days, months, and years. No doubt, these counters would have had to have been quite robust as they would have been exposed to many years of wind, rain and snow.

Figure 2. Plan of Darvill’s Stonehenge solar calendar’s middle area and the numbering for the calendar, not to scale. (Bournemouth University)

Figure 2. Plan of Darvill’s Stonehenge solar calendar’s middle area and the numbering for the calendar, not to scale. (Bournemouth University)

Year Zero - Day Zero

The calendar begins on the day of the winter solstice sunset (21st December) when the sun was seen to set along a north-east / south-west axis which, according to Darvill, is the only astronomical alignment needed at Stonehenge. The next day is when the year begins with the placing of a counter at Stone No1. Then, daily, the counter moves clockwise around the circle of sarsen stones until it reaches Stone No 30, which marks the end of the first month, from then on, eleven monthly, rotations of moving the counter past each sarsen stone around the Sarsen Circle culminated with a total of 360 days to which the five epagomenal days are added by moving the counter around each of the five of the Trilithon settings (Figure 2). Finally, a marker is moved around the four station stones to provide a means of keeping tally so that a sixth day could be added to the intercalary month every fourth year.

Overall, the operation of the calendar sounds simple enough but let us look at the detail. The start of the calendar begins when the midwinter sunset was observed at Stonehenge, let us call it zero-day (Figure 3). But what if there was a cloudy sky? This would cause a delay (to “starting the calendar-array) potentially for a full year. Moreover, there is no resilience built into the calendar for error or losing count during its operation. What would happen if, say, the counters marking out year 3 and day 257 suffered an error, miscount or confusion as to where to place a counter? The solution is that the calendar would have to be reset back to zero-day and to do that, we would have to wait for the next winter solstice sunset.

Figure 3. The Winter Solstice sunset at Stonehenge marks the start of the calendar. (Author provided)

Figure 3. The Winter Solstice sunset at Stonehenge marks the start of the calendar. (Author provided)

Besides the problems of resilience, there are also the difficulties of recording the vast number of days which the calendar will accumulate. Given that the calendar was set up to monitor at the very least a period of the four quarter days across four years (which is what the four station stones were used for) then, overall, it would accumulate 1460 days, 48 months and, of the course of four years.

Alternatively, Stonehenge was built to last and given that the sarsen features were raised around 2500 BC, the calendar could have been in operation for at least the 250 years (until, that is, when the incoming European Bronze Age people genetically replaced the indigenous Neolithic people, circa 2250 BC).

Now, we have some monstrous figures to absorb. Over this period, the calendar would record some 91,131.25 days; 3000 months; and of course, 250 years. These numbers are staggering for a Neolithic preliterate culture that has produced no evidence of writing at all (or the ability to record such data). And, if the people were using counters to mark off this long passage of time, then they would have required thousands of them, but no such counters have ever been recovered from Stonehenge.

Having considered how Darvill’s calendar could work, I finally do have to ask is whether a stone-built structure was actually required. Surely, three lines of wooden post, set out in a north-east to south-west direction, would work just as well to building a complex stone structure. Line One could contain 30 posts (in place of the Sarsen Circle); line two could contain 5 posts (in place of the Trilithons) and line three could contain 4 posts (in place of the four station stones). Certainly, this would have avoided the logistics of building those huge sarsen stone features at Stonehenge, which required thousands of people to work as much as 12 years to complete. The big question is why bother employing such human effort into making a calendar when a three lines of timber posts would effectively achieve the same purpose. Even better though, knots in string would provide a simpler solution.

Sunrise at Stonehenge and a new solar day! (Nicholas / Adobe Stock)

Sunrise at Stonehenge and a new solar day! (Nicholas / Adobe Stock)

The Stonehenge We Deserve?

For all the reasons I have discussed throughout this article, I doubt that Darvill’s Stonehenge solar calendar will progress beyond a hypothesis. More so because it is so easy to project numbers onto the architecture of Stonehenge. Let me provide an example to show just how easy it is. Now, I must stress that this example is very much my own “silly” proposal but the more you consider it, the more believable it becomes:

Let us take the word Stonehenge itself and substitute its letters for their equivalent place-numbers as they appear in the alphabet. Thus,

S = 19; T = 20; O = 15; N = 14; E = 5; H = 8; E = 5; N = 14; G = 7; E = 5.

When we add up all the numbers, we get a total of 112. Now, this total matches the 112 ft distance for the shorter sides of Stonehenge’s Station Stones rectangle. Divide 112 by two and the answer is 56, which matches the 56 Aubrey Holes at Stonehenge. Multiply 112 days by 3 ¾ (the ancient equivalent for the nearest calculation for pi) and the answer is 364 days, which is just one day short of Darvill’s solar year.

Take the letters E (5) T (20) E (5) and we have the 30 the thirty stones of the Sarsen Circle. A single letter E (or number 5) equates to the five Trilithons. Let us consider the letter S which equals the number 19 or the 19 years nodal cycle of the Moon as it orbits the earth. It also corresponds to the average 19 ft width of Stonehenge’s inner bank.

I could go on. But, as you can see, there are so many ways to play around with the numbers at Stonehenge, so it does not surprise me that researchers from time to time will be able to produce serendipitous ideas.

Dr. Hill’s book, ‘ The Recumbent Stone Circles of Aberdeenshire: Archaeology, Design, Astronomy and Methods’  is available at:

Top image: Darvill’s Stonehenge solar calendar theory is fascinating and the author of this article put it to the test! Source: Author provided

By Dr John Hill


Darvill, T. 2022. Keeping time at Stonehenge. Available at:

Hill, J. 2009. Design your own Stonehenge using the Occam’s Razor Solution. Trafford Publishing.



and still I believe that Darvill has a hypothesis that needs a non antagonistic review. John Hill simply rips Darvill’s approach apart, In my view in an unfair manner as Darvill is not here to defend his position of which he may well be able to do so. We have no evidence of the builders literacy or numeracy but that does not mean to say they weren’t. 

Dr. John Hill's picture


Dr John Hill is an experimental archaeologist who investigates the architectural designs of British Neolithic structures - domestic and ritual monuments.  He uses his experimental methods to determine how the Neolithic communities could have constructed complex architecture using both rudimentary... Read More

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