Thursday, 20 October 2016

The strange case of the dig for the Stonehenge tunnel

Following my concerns about the exploratory excavations for the Stonehenge Tunnel and how if the tunnel portal was built there and it was floodlit it would impact on the winter sunset solstitial view from Stonehenge  Mike Pitts takes me to task on for saying that position A1 on the plan below (borrowed from his blog posting so we are all using the same plan) is on the Winter Solstice Sunset Alignment.

As he points out it is important to point out that the position of the tunnel portal hasn't been decided but a plan with it at A1 is one of the options and that it "scored highly on its OUV impact"... "OUV. That’s “outstanding universal value”, a concept that is taken very seriously in assessing any changes in the landscape. How would a tunnel portal so close to the stones affect OUV, bearing in mind floodlights at night (if such things were visible, they’d be a problem all year round, not just on midwinter day)? I’d say very badly."

The OUV component that concerns the sightlines is discussed on the UNESCO page

The integrity of sightlines within the Stonehenge WHP

In assessing the integrity of these sightlines today, we make the assumption that they were largely kept clear in the Neolithic and Bronze Ages, so that the monuments could be used in the way in which we presume they were used, with the sun or moon rising or setting behind distant horizons visible from the monuments themselves. The sightlines are shown in (this figure).

Astronomical sightlines at Stonehenge World Heritage Site and the surrounding area, with their end-points on horizons. These should be treated as indicative rather than necessarily exact. The WHS area is shaded in yellow. Produced by Nick Hanks, Historic England, February 2015. © Crown Copyright and database right 2015. All rights reserved. Ordnance Survey Licence number 100024900

Sightline from Stonehenge looking southwest (midwinter sunset)

There is a growing consensus that the midwinter sightline was more important than the midsummer one, as discussed above. Today the integrity of this sightline, and its intermediate ridge lines and final horizon, is marred. Looking out from Stonehenge, the first problem is the A303 (0.5 km), which runs relatively close to the monument, and presents a considerable visual and noise intrusion to this alignment. Moving further south-west, the round barrow known as the Sun Barrow—which is on the alignment and on the Normanton Down ridge line—is intact (0.9 km), but the sightline then quickly runs into the plantation known as Normanton Gorse (1.1 km), which obscures it. Still further south-west is another plantation known as The Diamond (2.2 km), before the alignment continues towards the place that would form the visible horizon from Stonehenge in the absence of intervening vegetation, at Oatlands Hill to the west of the A360 road (and outside the WHP) (4.4 km). This horizon is also obscured by yet another plantation, at The Park. The sightline probably ends at the site of a much later Iron-Age/Romano-British settlement. It is difficult to determine the exact place because the various obstructions mean that we must rely upon computer modelling.

As closely as I can I have overlaid the Ordnance Survey map with position A1 and the UNESCO Southwest Sightline. My calculation is that the centre of the sightline is 60m from the centre of A1. With the margin of error, the width of the sightline and the size of a tunnel portal I would say that is pretty close to the portal being on the sightline, too close for my liking.

Click pictures to enlarge.

It is worth pointing out that it isn't just the central line at Stonehenge. The Station Stones also align to the midwinter sunset so one could fairly consider the solstitial line at the monument to be nearly 100m wide.


  1. As an aside to this, did you ever wonder where the idea of stone circles versus henges came from?

    The pollen records for much of lowland Britain at the time of what Mike Pitts terms the Hengeworld culture/religion was fairly open hazel scrub. However, at this time if we assume that the same religion was current across the whole of the country, we see an interesting set of monuments developing.

    In upland areas, stone circles made of varying sizes of stones were commonplace. In lowland areas, timber circles and henges were the replacement for stone circles.

    From a purely practical point of view, this actually makes sense. If you are interested in marking out astronomical movements and are, as is universal with humans, somewhat lazy then if you can get away with a permanent marker like a stone, then that is what you do.

    In upland areas then, where sightlines to the horizon are clear, you use stones on a levelled surface.

    In lowland areas where scrub obscures the horizon, you use either very tall timber posts that project above the scrubby horizon, or you create your own artificial horizon with a henge bank.

    This, BTW, is why there are different ditch positionings on different henges. The ditch isn't the important bit of a henge, the important bit is the bank top, which when in use probably had some sort of marker system (now long since eroded away) on the top to mark the various sightlines, together with some sort of "Stand here" marker inside the body of the henge.

    1. Interesting, thanks. I have previously refered to the post hole sites on top of the Stonehenge bank that may have been so used. Food for thought.

  2. Hi Dan,
    I have discovered that ditch-and-bank systems are generally level across a henge, regardless of topography, so the 'artificial horizon' idea is a good one, also proposed by several people.

    But at many sites - particularly Stonehenge - very few features have a single purpose, being layered with other meaning as well. This said, I believe that both the ditch and the bank were important to a couple of other concepts, while the painstaking labor of constructing them is not the least rationale.

    Few have taken flora into consideration and I'm pleased that this aspect is coming into its own.

    The locations on the bank that sport postholes certainly appear to indicate a 'Stand Here' motive.