Thoughts on Bluestone Trilithons

Within the collection of bluestones at Stonehenge are several interesting examples that show distinct signs of having been part of independent, tooled, structures.

Stone 36 and Stone 150 are clearly lintels having mortise holes worked into one of each of their faces, in much the same way that the lintels of the outer sarsen circle and inner horseshoe of sarsen trilithons do.

Stone 150 is quite rounded, and lies prone in the turf in the NE quadrant of the bluestone circle but Stone 36 is far more elegant and is almost entirely buried in the southern quadrant - in fact 36 is arguably the finest dressed stone on the site.

Stone 150

Stone 36

Stone 36, having been lifted for inspection during the excavations of 1954

Stonehenge plan showing the positions of Stones 36 and 150
© Anthony Johnson, annotations by Simon Banton
https://creativecommons.org/licenses/by/3.0/deed.en

As Julian Richards writes, in "Stonehenge - The Story So Far (2nd ed.)", referring to Atkinson's lifting of Stone 36 in 1954:

Apart from its sheer aesthetic qualities, Stone 36 posed some interesting questions. Along with stone 150 it was the second bluestone lintel to be identified and there were the uprights to go with them, pillars in the bluestone horseshoe that showed signs of having originally had tenons. So Atkinson could suggest a phase of ‘tooled bluestones’ which must, as there were now two lintels, have included at least two miniature trilithons. These, on the evidence of the mortice holes in the lintels would have looked very different from the much larger sarsen examples. The lintels would have extended beyond the edges of the slender pillars on which they perched, the space between the pillars and the height of the lintel sufficient to allow people to pass through.  The remarkable Stone 36 also provided evidence that this was not a short-lived structure. One of its mortice holes was surrounded by a shallow depression, presumably a carefully worked seating for the upright on which it sat, and within this hollow the surface of the stone appeared worn, even polished. This did not appear to be deliberate but more the result of friction, perhaps caused by the expansion and contraction of the touching stones. But such a polish would only develop very slowly, suggesting that these stones must have stood as trilithons for many years.

Could these two bluestone miniature trilithons have been the archetypes that eventually gave rise to much larger echoes of similar design in the enormous sarsen trilithons?

If so, then what could have been the intent behind the original creation of the bluestone versions? And where were they erected? Clearly not close to the current positions of 36 and 150 since they are remote from their supposed companion uprights which are components of the inner bluestone horseshoe arrangement and which carry the battered down remnants of tenons on their upper surfaces.

These are all repurposed stones - the bluestones have been rearranged a number of times in prehistory - and 150 in particular has been used, finally, as a pillar of the bluestone circle which was oriented so that its mortise holes would not be visible from the interior of the monument.

Bluestones have a remarkable capacity for being used as lithophones - "rock gongs" if you like. When found at their outcrops in the Preseli Hills in South West Wales, experimentally striking them with a rubber mallet or a deer antler will soon discover that certain ones that will "ring" like a bell.

They have to be positioned just right - balanced without being buried in the ground so that they can resonate when struck. The following video shows my attempts at getting a note out of a number of examples in 2023.

If there were two bluestone trilithons at some point in Stonehenge (transported there having been dismantled from an earlier monument in Preseli, perhaps), could the design have been in an effort to support two appropriate stones above the ground so that they could be easily "rung"?

What are the implications of such a suggestion? Is there an acoustic aspect to the use of Stonehenge that has been hinted at by a number of other researchers? One which employed the bluestones?

Are the bluestone trilithons in fact engineered sound sources? Maybe the "voices" of the stones were thought to have been in some way special in their own right, and bringing them to sing at the site of the future Stonehenge was important for an unknowable (to us) reason.

Given that the final arrangement of the bluestones at Stonehenge has them all either fallen, half-buried, or deeply embedded in the chalk (in the case of the upright ones) it seems that if they did have an original acoustic purpose then this was subsequently either forgotten or discounted by the people who incorporated them into the much later monument - even if they did echo their form in the horseshoe of enormous sarsen trilithons.

Stone 11 Shadow Effect

Stone 11 is the mysteriously half-height, half-width upright in the southern quadrant of the outer sarsen circle at Stonehenge.

Plan of Stonehenge indicating position of Stone 11

Stone 11 seen from the south

Several suggestions have been made to explain its curious dimensions - that the builders ran out of bigger stones, that it's a reused lintel, that it marks a division of the 30 uprights into three groups of 10 (the other marker being Stone 21) for calendrical reasons...

The 2012 Antiquity paper "Stonehenge Remodelled" (Darvill, T. et al. (2012) ‘Stonehenge remodelled’, Antiquity, 86(334), pp. 1021–1040. doi:10.1017/S0003598X00048225) offers:

...stone 11 (south) is narrower and shorter than the others perhaps to somehow mark the southern entrance (or it may even have been a later replacement).

None of those explanations have ever felt entirely satisfactory to me.

Recently I was watching Dr. Terence Meaden's video presentation to the 2024 Megalithomania Conference, on the topic of Pytheas the Greek's voyage to Britain and Thule.

Terence is always interesting and has had enlightening things to say about megalithic structures for decades. It was he that pointed out, for instance, that the Heelstone casts a shadow that penetrates into the centre of Stonehenge on the Summer Solstice (see "The Shadow of the Heelstone" on this site for more info).

While he was explaining his hypothesis that Stone 11 is of reduced height to represent "half" in the count of sarsens in the outer circle - ie that the circle conceptually held 29.5 stones rather than 30, and so could be used as a lunar calendar count, twelve times round it making 354 days then continuing the count on to Stone 11 would bring the day tally up to 365 and hence one solar year - he put up this diagram from his 2017 paper "Stonehenge and Avebury: Megalithic shadow casting at the solstices at sunrise":

Fig. 7 from "Stonehenge and Avebury: Megalithic shadow casting at the solstices at sunrise"
Journal of Lithic Studies (2017) vol. 4, nr. 4, p. 39-66 doi:10.2218/jls.v4i4.1920

Terence points out that the shadow of Stone 11 falls on Stone 40 at Winter Solstice Sunrise, and suggests that the male Stone 11 deliberately interacts with the female Stone 40 in this way.

Those familiar with his work will recognise this as a common theme in his research - phallic upright stones casting shadows onto recumbent receiving stones at key times in the year.

The next image in his presentation gave me goosebumps.

Stone 11 just after sunrise near Winter Solstice with the Sun at its rising azimuth of 2500 BCE

The shadow of Stone 11 can clearly be seen clipping the fallen Stone 14's right hand end (its upper end when erect), and Stone 40 (a bluestone) is directly behind this fallen sarsen lying prone in the turf - not visible in this shot, exactly under Stone 11's shadow. But that's not what grabbed me.

The shadow of Stone 11 continues across the ground and directly intersects with Station Stone 93! This contrast-enhanced closeup of Terence's image shows it well.

Stone 11's shadow hitting Station Stone 93

For this to happen, Stone 11 has to be a very particular height and width - any wider and its shadow will not match the width of Station Stone 93, any taller and the shadow will extend well beyond 93's peak.

We have to remember to account for the shift in the Earth's axial tilt from 24° to 23.5° since 2500 BCE. 

At winter solstice 2500 BCE, the Sun reached "full orb" over Coneybury Hill at an azimuth of 130° 20':

Full orb winter solstice Sun position, 2500 BCE

In our era, on the 27th December 2014 (when Terence's photo was taken), the Sun is at a higher altitude when it reaches this azimuth:

Sun's position on 27th December 2014 when it reaches azimuth 130° 20'

Its altitude in our era is 1° 6', back in 2500 BCE it was 0° 26' - a difference of 40' of arc. This difference puts the tip of Stone 11's shadow fractionally lower on Stone 93 now than it would have been then.

It seems likely that Station Stone 93 would have been completely and exactly engulfed by the shadow of Stone 11 cast by the full orb risen Sun at winter solstice in 2500 BCE.

Drawing this shadow line on the reference plan of Stonehenge from "Stonehenge in its Landscape" (Cleal et al, 1995), along with the secondary solstice axis identified originally by Gordon Freeman (see "The Secondary Solstice Axis" on this site) highlights their parallel nature.

Stone 11 shadow (black line) and the secondary solstice alignment (red line)

Zooming in on this, and incorporating the plan of the parchmarks for the missing stones 17, 18, 19 and 20 from "Parchmarks at Stonehenge, July 2013" (Banton, S., Bowden, M., Daw, T., Grady, D., & Soutar, S. (2014) Antiquity, 88(341), 733-739 https://doi.org/10.1017/S0003598X00050651) reveals an elegant aspect to this shadow line.

Closeup incorporating the plan of the parchmarks identifying the positions of Stones 17, 18, 19 and 20

... the shadow of Stone 11 (the black line) passes exactly through the gap where missing stone 18 and 19 would have stood (if indeed, they'd ever been erected - the jury's out on that one) - so it would not have been blocked by them.

In the end what does this mean?

It appears possible that Stone 11 was positioned and shaped to create a shadowplay effect at winter solstice when Stonehenge was built, one that targeted Station Stone 93 very precisely both in position and size.

If Stone 11 was fatter and taller, this wouldn't have worked so neatly.

All that remains to be explained is the leaning nature of Stone 11, because it is not perfectly upright.

Stone 11 leaning towards the south

... how does this affect things? Is it intentional? I'm looking at this picture and noticing that the right hand edge of the stone is almost perfectly vertical, compensating for the lean.

The investigation into that is a story for another day.

Many thanks to Terence for giving me permission to use his images.