The Bulford posts in 3D

Open this to understand this post: https://timdaw37.github.io/bulford-posts-3d/

Drag to rotate, right-drag to pan, scroll to zoom. Click a pit for its name and coordinates.

Figure: live viewer, along the posts, midsummer, first gleam, 2950 BC.

In PAST 113, Phil Harding, Matt Leivers and Fabio Silva publish two Late Neolithic post-pits at Bulford, about 120 m apart, and argue that they mark the midsummer sunrise and midwinter sunset of around 2950 BC. Harding’s excavation is the reason we have the pits at all. Out of dozens of ordinary scrapes on that hilltop he picked the two that were actually built as structural post-holes — a metre across, thirty inches deep, ash in the fills — and only then asked what they pointed at. That is the right order. The PAST paper is a proper account of a real discovery, and Silva’s insistence that a claimed solstice has to be tested against the local skyline, not a round number from Stonehenge, is the right question.

In June, before PAST was out, I put down some sceptical notes on the news reports: a crowded pit field, a topographic grain that favours certain orientations, and not enough published geometry to tell coincidence from design. The article now gives the plan, the azimuths they used, and the argument. The next thing I wanted was to stand on that plan and look.

So here is a 3D model of the published figure. All 39 pits from the Wessex plan are marked. The two alignment posts stand in their holes, 8647 at 2 m and 9019 at 4 m, as the paper draws them. The ground is OS Terrain 50 with a 1 m LiDAR inner patch; you can switch to map or aerial. The sun sits on Bulford’s own skyline, with first gleam, half orb and full orb as alternatives, at 2950 BC, 2500 BC or today.

Figure: the Terrain 50 landscape with the post-line.

From the plan the posts run 48.12° grid, 48.31° true. On this horizon, midsummer first gleam in 2950 BC comes up at about 48.88°; midwinter last gleam goes down at about 229.5°. Neither sits on the timbers. First gleam is the closer of the two, about half a degree off. Sunset is further. We do not have the Wessex GNSS coordinates of the pit bases — they have not been released — and every position in the model is digitised from the published 1:1000 plan. Two independent readings of 8647 and 9019 agree to 0.2 m, which is good enough to look and not good enough to prosecute a fraction of a degree. The miss may be in the plan, in the skyline, or in my arithmetic. I would rather put the model out than pretend otherwise.  Ruggles’ working rule is that half a degree is as tight as a two-post solar line can be, about a degree is a fair prehistoric axis, and two degrees is the chance envelope

Have a go. Start with Along posts, Midsummer, 2950 BC, first gleam. Then Midwinter. If the sun and the posts do not agree on your screen either, we are looking at the same thing.

Harding, P., Leivers, M. and Silva, F. 2026. A newly discovered solstitial post alignment in the Stonehenge landscape at Bulford. PAST 113, 2–5.

Earlier notes: Bulford: pits, double henges and a claimed solstice alignment. Code: github.com/TimDaw37/bulford-posts-3d.

Terrain: OS Terrain 50 and EA 1 m LiDAR © Crown copyright (Open Government Licence). Map: © OpenStreetMap contributors. Aerial: ESRI World Imagery. Drafting with Grok; the errors are mine.