Saturday, 12 September 2026

Britain, 5000–2000 BC: no ice, no catastrophe, a familiar climate

An interactive, fully referenced viewer of published palaeoclimate proxies for Britain across the Stonehenge-building millennia is now online: 

Climate of Britain, 5000–2000 BC.

It draws on twelve independent proxy records: peat water tables, cave speleothems, lake chironomids, ice cores, ocean sediment, a pollen-based reconstruction and tree rings, each carrying its own citation, archive link and stated uncertainty. Three findings fall out of it directly.


Stonehenge - 2013 - Tim Daw

The Avon would not reliably have frozen thick enough to drag stones over

One proposed route for moving sarsens to Stonehenge has them dragged across the River Avon on a surface of thick winter ice. The pollen-based reconstruction gives a direct check on this: mean January temperature for Wessex across all four millennial slices in the window comes out at 2.7–4.2 °C — above freezing, and close to the modern Boscombe Down January average of 4.0–4.6 °C. A monthly mean sitting a few degrees above 0 °C does not rule out individual cold spells or short-lived ice, but it argues against the sustained, reliable deep freeze that dragging multi-tonne stones across a river would need. On this proxy evidence, an ice-covered Avon load-bearing enough for sarsen transport looks like the exception rather than something that could be counted on.

Glacial transport of the stones themselves is a separate and much earlier question, belonging to the last glaciation many thousands of years before this window opens; it isn't addressed by this dataset one way or the other.

No coherent climate catastrophe, and no population-ending event

The most-cited candidate for a climate-driven population collapse in this period is the "4.2 ka event," dated to around 2200 BC. Roland et al. (2014) tested this directly against the British and Irish peat record and found no regionally coherent, prolonged shift to wetter or colder conditions at that date — the four records that do show any change disagree with each other in timing, duration and structure. The one genuine regional exception is a centennial cold interval in eastern England dated to roughly 4320–4210 cal BP, identified from lake isotopes at Diss Mere and independently from tree-ring isotopes in the Fenland — real, but local to eastern England, about a century long, and not an island-wide catastrophe. Nothing in the compiled proxies supports a climate event severe or widespread enough to end a population.

The climate was not very different from today's

The pollen-based reconstruction (Mauri et al. 2015) gives four millennial temperature and rainfall estimates for the Wessex grid cell containing Stonehenge, referenced against the Boscombe Down climate normals — the nearest long Met Office record. The central estimates:

SliceAnnual mean °CJuly °CJanuary °CAnnual rainfall mm
5050 BC9.617.42.7~730
4050 BC10.116.74.2~815
3050 BC9.616.73.8~870
2050 BC9.616.54.0~840
Boscombe Down, 1971–20009.8516.754.0736
Boscombe Down, 1991–202010.4217.14.6783

Every one of the four central annual-mean estimates sits within half a degree of the modern 1971–2000 average, and all are a little cooler than the current (1991–2020) average — Wessex has warmed slightly since, rather than the Neolithic and Bronze Age being markedly colder than today. Including the full published uncertainty (±1σ, propagated across the window), the plausible annual-mean band is roughly 8.6–11.1 °C: comfortably straddling both modern baselines. Winters may have run a little cooler in the earliest slice (5050 BC: ~2.7 °C January vs 4.0–4.6 °C today), but by the Beaker period the estimate is close to indistinguishable from now. Rainfall is centrally similar to modestly wetter than today, with an uncertainty band wide enough to include "about the same." None of this supports either an unusually harsh or an unusually benign climate: mid-Holocene Wessex was, within the resolution these proxies allow, a maritime temperate climate much like the one standing at Stonehenge today.

Full series, citations, archive links and uncertainty notes for every proxy are in the interactive viewer.

Friday, 11 September 2026

The Devil Is In the Detail

A new paper sources Yorkshire's Devil's Arrows to Brimham Rocks, 18 km west. The zircon evidence for that is sound, but the stratigraphy behind it needs a correction, and the case against glacial transport is stronger than the paper itself makes it.


Clarke, Leary and Kirkland have a new paper in Proc. R. Soc. A (20260504). Peel samples were taken from the three standing stones at Boroughbridge, and roughly a kilogram of rock each from Brimham Rocks and Plumpton Rocks. Detrital zircon U–Pb ages from the Arrows match Brimham (Kolmogorov–Smirnov p = 0.77) and do not match Plumpton (p = 6.7 × 10–5). Historic England's long-standing attribution to Plumpton is the wrong outcrop.

That result stands. The stratigraphic framing around it does not. The paper describes Brimham and Plumpton as "both Upper Plumpton Grit outcrops... the same Namurian stratigraphic interval." The British Geological Survey's own lexicon says otherwise, and checking it against the 1:50k mapping changes what the zircon match is actually evidence for.

What they actually dated

The Devil's Arrows stand on Triassic Sherwood Sandstone and are not made of it — the paper establishes this cleanly, on both lithology and zircon spectrum, and it isn't in dispute. What they are made of is Kinderscoutian Millstone Grit, deposited around 318 Ma by the Pennine river system. The paper states that its two comparison outcrops, Brimham Rocks and Plumpton Rocks, "are both Upper Plumpton Grit outcrops... the same Namurian stratigraphic interval." Checked against the field literature for each site individually, that statement is wrong, and it's wrong for reasons independent of each other — the two outcrops aren't misidentified by the same error, they're simply two different units.

Brimham. BGS's own excursion guide to the site, describing the rock as sampled in the field rather than as read off a map, states that "the spectacular natural cliffs and tors of Brimham Rocks are carved out of a plateau of Lower Brimham Grit (mid-Namurian)." Soltan and Mountney's 2016 study of the outcrop's channel architecture — a paper Clarke, Leary and Kirkland themselves cite, for basin-scale heterogeneity — captions their own photograph of the site the same way: "Lower Brimham Grit succession exposed at Brimham Rocks." The BGS lexicon records Lower Brimham Grit under the alternative name Lower Plompton Grit (LPG), part of the Hebden Formation, sitting above the Ure Shell Bed and below the Eccup measures. Three independent descriptions, converging on the same unit: Brimham Rocks is the Lower leaf.

Plumpton. The BGS memoir for the Harrogate sheet (62) puts its cover photograph exactly where the dispute sits: Lover's Leap, Plumpton Rocks, captioned as "naturally sculptured crags of Upper Plompton Grit at its type locality." Plumpton Rocks isn't merely similar to the Upper leaf — it's the section BGS uses to define it. Cooper's Knaresborough Gorge excursion notes, and the Denys Smith memorial trip report covering the same ground, both describe the Lower Plompton Grit as exposed separately, a few kilometres away at Knaresborough Gorge, beneath the Upper leaf in the local succession, not at Plumpton Rocks itself.

So the two outcrops the paper compares are the lower and upper leaves of the Plompton Grit, divided by the Eccup Marine Band — not, as stated, the same stratigraphic interval. This isn't a map-reading disagreement over which of two adjacent colours a dot falls in; it's the paper's named comparison localities being described, independently and repeatedly, as different units in the literature it already draws on for other purposes. It also isn't an incidental distinction. The Hebden Formation's lower part is "a turbiditic facies... with laterally impersistent and locally thick, massive, coarse to very coarse-grained sandstones" — channelised, not a blanket sand — while the upper part is "sheet-like, laterally persistent." Individual channel bodies of that kind can carry genuinely distinct detrital zircon signatures, which is the mechanism the paper needs for Brimham and Plumpton to differ in the first place. Correcting the stratigraphy doesn't weaken the zircon result — Arrows vs Brimham, KS p = 0.77; Arrows vs Plumpton, p = 6.7 × 10–5 — it explains it.

Plumpton Rocks — the outcrop the paper samples and compares against — is consistently described in BGS excursion literature (Cooper and Burgess's 1993 Harrogate memoir, and the published Knaresborough Gorge excursion guides) as the Upper Plompton Grit. So the two sampled outcrops are not "the same Namurian interval": they are the lower and upper leaves of the Plompton Grit, separated by the Eccup Marine Band. The paper's own Kolmogorov–Smirnov numbers already say this — Arrows vs Brimham not significantly different, Arrows vs Plumpton clearly different — the caption just doesn't correctly name why.

The place is Plumpton Rocks, with a U, used throughout the paper and by Historic England. The adjacent park and houses are Plompton as is the geological unit Plompton Grit, with an O, Both the Lower and Upper leaves carry it: LPG and UPG. Reading "Plumpton Rocks" against "Plompton Grit" without noticing the two are spelled differently makes it easy to miss that the lexicon is also carrying two separate codes under that name, not one.

It also isn't an incidental distinction. The BGS lexicon's lithological description of the Hebden Formation splits it into a lower part — "a turbiditic facies... with laterally impersistent and locally thick, massive, coarse to very coarse-grained sandstones" — and an upper part of "sheet-like, laterally persistent" sandstone. The Lower Brimham/Plompton Grit is channelised, not a blanket sand. Individual channel bodies of that kind can carry genuinely distinct detrital zircon signatures, which is the mechanism the paper needs for Brimham and Plumpton to differ in the first place. Correcting the stratigraphy doesn't weaken the zircon result; it explains it.

Click to enlarge
 BGS Geology 50k bedrock + superficial, © UKRI 2026. Frame BNG 415–445 E, 448–500 N km.

The map

The 50k sheet covering Brimham, Boroughbridge and Plumpton (dots are GetFeatureInfo point samples, not filled polygons) shows the Lower Brimham/Plompton Grit at outcrop in one cluster: the Brimham Moor tor field and the ground immediately west of it. The same leaf reappears elsewhere on the sheet, but under cover — beneath Devensian till north of Hack Fall, and beneath Vale of York Formation roughly 12 km west of the Arrows — rather than exposed. The Upper leaf is a separate storey above it.

A closer inset around Plumpton shows both leaves printed in the same yellow on the standard 50k colour scheme, distinguished only by lexicon code: Lover's Leap itself sits on Upper Plompton Grit (UPG), with a strip of Lower Plompton Grit (LPG) — the same unit as Brimham and the Arrows — running immediately to its west, separated by thin intervening measures. That strip was not sampled.


6 × 6 km, BNG 432–438 E, 450.5–456.5 N. Same WMS yellow, two lexicon codes.

What the air photos add

Brimham Moor is an open plateau of exposed stacks — individual joint blocks, already the size of pillars, visible from the path and from the air (Geograph squares SE2064 and SE2065). Plumpton, by contrast, is a lake set in woodland with a single crag along one shore — Lion's Den, Lover's Leap, Needle's Eye — roughly 10–12 m above the water, part natural and part quarried, matching Historic England's listing description. The fields west of the lake, where the 50k map places the Lower Plompton Grit at outcrop, are smooth pasture with no visible scatter of grit blocks.

PlaceWhat the air photo showsLeafPlausible as a stone source
Brimham MoorOpen plateau of stacksLower (LOBM/LPG)Yes — blocks already detached along natural joints
Plumpton lake cragOne wooded cliff, 10–12 m, part quarriedUpper (UPG)Wrong leaf on the zircon evidence; already excluded
Fields west of the lakeSmooth farmlandLower (LPG), per the mapNot visible as exposed rock from the air


Brimham Rocks, "Idol Rock" — Penny Mayes, Geograph 1184, CC-BY-SA 2.0.

Against glacial transport

Late Devensian ice in the Vale of York moved NNW to SSE, down-valley — the wrong direction to have carried anything off the Pennine edge onto the Boroughbridge ridge, and no reconstruction maps a westerly conveyor off Brimham Moor at all. The excavated stone sockets — 1.5 m deep, flat-bottomed, and of matching dimensions at all three stones — already show the row was set by hand, not left in place by melting ice. Two further lines point the same way: the Arrows carry deep, weathering-fluted grooves and an elongate, naturally joint-bounded shape matching Brimham's own fracture pattern (fig. 6B), not the rounding expected of a boulder that has travelled inside moving ice; and all three stones share a single, statistically indistinguishable zircon population (table 1), closer to what one quarried outcrop produces than to the mixed assemblage typical of glacial till.

Once human erection is established — and the sockets establish it regardless of source — the question of transport is no longer whether people moved the stones, only how far. A group that can lever a pillar off a joint face and walk it into a socket a hundred metres away has already demonstrated the method; eighteen kilometres from Brimham is a longer version of the same task, not a different one. Glaciation, by contrast, still needs an ice path the reconstructions don't map, and still leaves the fluting, the jointing and the single-source signature unexplained. What the ice-flow reconstructions cannot do, and the paper's own discussion concedes, is resolve or exclude a specific 18 km path between Brimham and Boroughbridge at the resolution the abstract implies — but by that point glaciation has already lost the argument on capability, and an unresolved ice model doesn't reopen it.

What still needs checking

Three things follow directly from the mapping and are not addressed in the paper:

  1. The Lower Plompton Grit strip immediately west of Lover's Leap — the same unit as the Arrows on the 50k map, closer to Boroughbridge than Brimham, and neither dated nor visibly exposed as a tor field from the air.
  2. Whatever Carboniferous sandstone actually lies at or near surface roughly 12 km west of the monument, under the Vale of York Formation.
  3. A second storey at Brimham itself — Soltan and Mountney (2016) already log two distinct channel systems within the tor field, which the single 1 kg sample cannot distinguish between.

Until those are checked, Brimham is the best-supported source among the outcrops that have actually been dated, not a uniquely identified quarry. The zircon evidence is good enough to rule out Plumpton and rule out the local Sherwood Sandstone; it is not yet enough, on its own, to rule out the other exposures of the same facies belt that lie closer to the monument and were never sampled.

References

  1. Clarke, A.J., Leary, J. & Kirkland, C.L. 2026. Deliberate prehistoric sourcing of the Devil's Arrows, Britain's tallest stone row. Proc. R. Soc. A 482, 20260504. doi.org/10.1098/rspa.2026.0504
  2. BGS Lexicon of Named Rock Units: Hebden Formation (HEBD); Millstone Grit Group (MG).
  3. BGS Lexicon: Lower Brimham Grit (LOBM) / Lower Plompton Grit (LPG).
  4. BGS Earthwise. Carboniferous rocks of upper Nidderdale — an excursion, Locality 1, Brimham [SE 212 670].
  5. Cooper, A.H. 2008. Permian and Carboniferous, Knaresborough — excursion notes. Denys Smith Memorial Trip, BGS Open Report OR/08/044.
  6. Soltan, R. & Mountney, N.P. 2016. Interpreting complex fluvial channel and barform architecture: Carboniferous Central Pennine Province, northern England. Sedimentology 63, 207–252.
  7. Cooper, A.H. & Burgess, I.C. 1993. Geology of the country around Harrogate. Memoir, sheet 62.
  8. Wilson, A.A. & Thompson, A.T. 1965. The Carboniferous succession in the Kirkby Malzeard area. Proc. Yorkshire Geol. Soc. 35, 203–227.
  9. Bateman, M.D. et al. 2015. Last glacial dynamics of the Vale of York and North Sea lobes.
  10. Clark, C.D. et al. 2022. The BRITICE-CHRONO reconstruction. Boreas.
  11. Historic England NHLE 1014705, Devil's Arrows.
  12. Historic England NHLE 1000535, Plumpton Rocks.

Contains British Geological Survey materials © UKRI 2026. Geograph photographs CC-BY-SA as credited on source pages.

Thursday, 10 September 2026

An Interactive model of the Stonehenge Landscape

 


A fully interactive virtual landscape of the Stonehenge area 

https://stonehenge-3d-flythru.netlify.app/

The latest Julian Richards video needed some graphics, which I was happy to help out with. As well as the maps I also produced this interactive Stonehenge landscape. There's a lot in it. 
I'm very proud of this one and my particular little favourite is looking underneath for the Wilsford Shaft. 

And there is a 3D topographical fly through of the Avebury Landscape -

https://avebury-3d-flythru.netlify.app/

Secrets of Stonehenge’s Hidden Landscapes | Stonehenge Access All Areas, Ep 10

Wednesday, 9 September 2026

The Wiltshire Long Barrow Gazetteer

The Wiltshire Long Barrow Gazetteer - https://timdaw37.github.io/wiltshire-long-barrows/

A hundred and twenty-nine Neolithic long barrows on the Wiltshire chalk — HER certain and possible, plus one modern mound at All Cannings that is mine. Gold markers you can trust; grey ones you should treat as possible. Where the earthwork still shows on the LiDAR chip, a rim arrow marks the long axis of the mound: the line of the bank, not the way a façade “faces”. Eighty-six arrows. Forty-three sites with no arrow, because nothing usable is there to measure.

People have always wanted a sentence for the set. They face the rising sun. They run along the ridges. They stand on the skyline, landscape controllers, meant to be seen from below.

We measured all three.

They do not face the sun as a shared design. The eighty-six axes spread. There is a gentle east–west smear and no spike at midsummer or midwinter. Give a random set of arrows the same two solstice targets and chance is as close as the real mounds. They sit nearer the contour than luck would put them. They do not glue themselves to the ridge. Half the sample is still more than thirty degrees off the local ground. West Kennet rides the nose of its spur. East Kennet, a mile away and the same tradition, cuts across it.

They do not stand on the skyline always either. Adam’s Grave does, and West Kennet, and a handful of others.  South Street and Lanhill, good surviving mounds, fail the test: often visible, almost never the crest against the sky.

Field, McOmish, Ruggles and Roberts already said so in other words. The map and the two notes are that argument with arrows on it.

Eighty-six Wiltshire long-barrow axes, each drawn both ways. The dashed lines are sunrise on a flat horizon at this latitude: midsummer, equinox, midwinter. They are drawn so you can see them. They are not a finding.

The longer notes:

Do Wiltshire’s long barrows stand on the skyline?

The short answer is no as a shared design — same family as the solar result. Some do (Adam’s Grave class). Many famous ones do not. Being visible on a ridge is not the rule.

Every arrow is on the map:

The Wiltshire Long Barrow Gazetteer

What follows is a first cut at a different question from the ridge-axis work: not whether the mound runs along high ground, but whether it was meant to stand on the skyline from approaches where you can see its length.


Standing on other people’s work

None of this starts from a blank field.

David Field and David McOmish, walking the chalk, kept saying the same thing in different words: long barrows sit with care in local ground; there is no single shared recipe. Clive Ruggles insisted prehistoric “display” claims have to survive a proper test, not a pretty photograph. Dave Roberts and colleagues, around Stonehenge, put local topography first and published the table. David Wheatley’s HER recreation and the Environment Agency county DTM are what let a county-scale check exist at all.

We add a systematic skyline-from-below sample on top of that work, not instead of it. If this note is useful, it is because those people already did the hard looking.


NOTE - Click photos to embiggen, and use The Wiltshire Long Barrow Gazetteer


Two sentences that get stuck together

People say long barrows “sit on the ridge” and mean two different things.

One is siting: the mound is on high ground. West Kennet is. Many others are. That is true and not the test here. The companion note already showed that long axes sit nearer the contour than chance, without gluing themselves to it. East Kennet, a mile from West Kennet and the same Cotswold–Severn tradition, cuts across the ridge. Same downs, two recipes.

The other is design as a skyline marker — a landscape controller — from approaches where the length of the mound shows: broadside views, not end-on. Does the crest sit against sky, silhouetted, from those wedges? Or is it only visible against rising ground beyond?

That is the question I wanted answered. “Along the ridge” was the wrong sentence.

Two photographs show the phenomenon the maps are trying to score. They are ground truth for those viewpoints. They are not a county rule.

Figure 1. Kitchen Barrow from a lower southern approach, 9 September 2026. The mound is the bump on the distant ridge, silhouetted against sky. That is a skyline-from-below catch.

Figure 2. West Kennet from the north, 22 October 2021. The long mound sits on the ridge skyline; people on the crest give the scale. 

Kitchen’s southern silhouette is what an Adam’s-class neighbour looks like in a photograph: a distant ridge bump, length showing, sky behind it. West Kennet from the north can do the same. The rest of this note asks whether those catches are typical of the defined approaches, or rare sweet spots.


What was measured

Take each barrow’s trusted long axis (the undirected bearing already on the gazetteer).

From that axis, open two perpendicular wedges — the bearings where the length is visible, about ±32° either side of broadside. Inside those wedges only, drop observers on a dense grid at road-to-ridge scale (roughly 0.3–2.5 km). For each cell, ask whether a line of sight to the crest is clear on the county Environment Agency DTM, and whether ground beyond the crest rises above that line. If it does not, the mound is the local horizon peak: skyline from below.

Maps are contour fields of that clearance, not a single corridor percentage. Green (positive clearance) means the crest sits above the far horizon. Red means you can often still see the mound, but against higher chalk beyond. Percentages are a blunt summary of the green.

Figure 3. The local four on the same frame. Blue dashed wedges are the length-shows approaches; yellow tick is the long axis; red dots are skyline hits. Green is silhouette; red is crest against rising far ground. Adam’s Grave is almost all green. Kitchen has a coherent southern catchment. West and East Kennet are mostly red, with small green pockets near the mound.

Ground truth before the computer: Kitchen’s southern silhouette (Figure 1); West Kennet from the north (Figure 2); Adam’s Grave from the Lockeridge approach; East Kennet from the nearer road. Pins and photos check that the model can catch real views when they exist.

Crest height is the 1 m LiDAR chip plus a modest reconstruction stick-up of 2 m. Eye height is standing height (1.7 m). Mild earth curvature and refraction are on. Contour-band nulls — random points on the same height band — are secondary. Named barrows should beat them if “designed skyline marker” is the claim.

This is not a ridge-axis test, not a Tilley-style walk, and not the Bulford solstitial horizon-altitude protocol. Do not mix the three.


The local four

Adam’s Grave, Kitchen, West Kennet, East Kennet. Same stretch of down. Same method.

Adam’s Grave

Figure 4. Adam’s Grave. About 88% of the broadside sample puts the mound on the skyline. The cyan X is the Lockeridge pin (~593 m north of the crest): clearance ≈ +5.4°. That is what an Adam’s-class silhouette looks like in these scores.

From Pewsey Vale to the south, and from the Lockeridge approach to the north, the scarp-edge mound is almost always the horizon peak when it is visible at all. Contour-band nulls average ~14%. A fake crest shoved 200 m downslope, in the earlier corridor run, collapsed to 0%. The Lockeridge pin sits squarely in the green.

Kitchen



Figure 5. Kitchen Barrow. About 32% skyline in the same frame, beating local nulls (~8%) by roughly four times. The southern wedge is the catchment that matches Figure 1.

Kitchen lands lower than Adam’s Grave but still real. The map shows a coherent southern / vale catchment and a thinner northern one. That is the photograph: a distant ridge bump from below, length showing. Not as dominant as Adam’s Grave. The named site outperforms random same-height ground.

West Kennet

Figure 6. West Kennet. About 60% of the broadside cells can see the mound; only 19% put it on the skyline. Median clearance is slightly negative. The green pockets sit close in, north and south of the crest. Most of both wedges are red: the ray through the mound continues onto higher chalk beyond.

West Kennet is the awkward one relative to reputation, and relative to Figure 2.

Corridor-style sampling — vale cells 1–5 km out, not restricted to broadside — made it look almost absent as a true skyline peak (~1%). Restricting to length-shows wedges at nearer range improves it to ~19%, and beats the local contour null (~6%). So there are pockets of silhouette, including from the north. Figure 2 is real. The model finds them.

Typical cells in the defined approaches still see the mound against higher chalk beyond more often than against sky. Geometry says why: from much of the northern Kennet valley the ray through West Kennet continues onto the East Kennet ridge and related ground. Raising the target (a taller reconstructed mound) barely moved the corridor skyline percentage. WK can silhouette from the north. As a fraction of the defined approaches it is not Adam’s Grave.

East Kennet

Figure 7. East Kennet. About 19% skyline, similar to its neighbour. The cyan X is the nearer road pin (~678 m north-east of the crest): clearance ≈ +1.2°, a genuine high-contour catch. The south-west wedge is almost entirely red.

East Kennet’s road pin sits in a coherent positive-clearance pocket on the north-east side. The earlier sample was too far; at ~0.7 km the mound does silhouette broadside. That does not make the rest of the approach an Adam’s-class catchment. Most of the south-west wedge sees the crest against rising far ground.

So: two strong local markers, two famous neighbours that do not carry the same score. Same downs, different recipes — again.

SiteAxisn% visible% skylineMedian clrvs null
Adam’s Grave136.0°22487.587.5+2.66°6.1×
Kitchen43.5°23039.131.7+0.59°3.9×
West Kennet84.5°22659.719.0−0.29°3.1×
East Kennet139.0°22644.718.6−0.13°2.4×

Ten more, same test

I flagged prominent and good-survival sites, same perp-wedge method: Winterbourne Stoke Crossroads (WS1), Whitebarrow, Giants Grave, Cold Kitchen Hill, Tinhead Hill, South Street, Horton Down, Lanhill, King Barrow, Amesbury 42. (Cold Kitchen Hill is not Kitchen.)

Winterbourne Stoke 1


Figure 8. Winterbourne Stoke 1, the great surviving mound at Longbarrow Crossroads. About 66% skyline — every visible cell in this sample is also a skyline hit. Median clearance +0.53°. The ratio versus null is only 2.6× because ridge nulls on this ground are high (~25%). Still the standout of the second batch.

WS1 is the pilot-2 headline. Field already flagged the mound as a topographic object first. The skyline maps agree: from the length-shows wedges at road-to-ridge scale, it behaves like an Adam’s-class catchment, not a solar instrument and not a coincidence of a pretty photograph.

The rest of the ten

Figure 9. Ten prominent / good-survival mounds on the same frame as Figure 3. Green catchments at WS1, Giants Grave, Amesbury 42, Cold Kitchen Hill and Tinhead Hill. South Street and Lanhill are dark red throughout.

Giants Grave and Amesbury 42 sit in a second tier near 42% skyline, both with slightly positive median clearance.

Figure 10. Giants Grave, above the Wylye. One wedge is a coherent skyline catchment; the other is almost empty. About 42% skyline overall — Kitchen-class coverage, strongly one-sided.

Cold Kitchen Hill and Tinhead Hill land around 30%, Kitchen-class coverage with the strongest positive clearance cores in the batch (about +1.2° and +1.1°). Cold Kitchen Hill is a separate monument from Kitchen; it happens to score in the same band.

Figure 11. Cold Kitchen Hill (ST83NW101), not Kitchen. About 30% skyline; median clearance +1.21°, the strongest angular core in this batch. The north-east wedge carries the catchment; the south-west wedge does not.

Horton Down and King Barrow beat their local nulls but are weaker in absolute skyline cover (~23% and ~20%).

Whitebarrow is often visible and rarely the true crest-against-sky silhouette (~14%).

The fails

Survival and fame are not the same as skyline design.

Figure 12. South Street. About 55% of the broadside sample can see the mound. Skyline hits: 0.4%. Median clearance −0.53°. The crest sits against rising far ground from almost every length-shows cell.

Figure 13. Lanhill. About 51% visible; 0% skyline. A well-known surviving mound, length showing from the sides, never the local horizon peak in this frame.

South Street sits in the Avebury landscape, a short walk from West Kennet. Lanhill is a Cotswold–Severn chambered long barrow with a good earthwork. Neither behaves as a skyline marker from the approaches where the length shows. That is the point of doing the work this way: the method that lights up Adam’s Grave leaves these two dark.

SiteAxis% visible% skylineMedian clrvs null
Winterbourne Stoke 135.0°66.266.2+0.53°2.6×
Amesbury 425.0°50.542.4+0.24°1.9×
Giants Grave9.0°46.542.0+0.25°2.2×
Tinhead Hill64.3°31.731.7+1.05°1.4×
Cold Kitchen Hill148.5°29.729.7+1.21°1.9×
Horton Down97.7°48.723.4−0.14°3.9×
King Barrow161.5°69.819.8−0.51°3.6×
Whitebarrow91.7°44.614.4−0.14°2.0×
South Street68.9°55.30.4−0.53°0.2×
Lanhill90.5°51.40.0−0.29°0.0×

Combined ranking (blunt)

Fourteen mounds. Rank by skyline fraction in the length-shows wedges. Numbers will move if the distance band, wedge width or vegetation model moves. The rank order is what I trust for now.

ClassSites (approx. % skyline)
StrongAdam’s Grave (~88%); WS1 (~66%); Giants Grave / Amesbury 42 (~42%); Kitchen (~32%); Cold Kitchen / Tinhead (~30%)
MidHorton Down (~23%); King Barrow / West Kennet / East Kennet (~19–20%); Whitebarrow (~14%)
FailSouth Street (~0%); Lanhill (0%)

A few mounds behave like length-on-skyline markers. A larger set of well-known names do not. West and East Kennet sit in the middle once you stop scoring them as corridor percentages and stop cherry-picking the sweet-spot photograph. The photograph remains true. It is not typical.


What that means

Visible on the ridge, like sunrise alignment, does not seem to be a factor — not a shared design rule for Wiltshire’s long barrows.

Local effects exist. Adam’s Grave and WS1 are not accidents in these maps. Kitchen, Giants Grave, Amesbury 42, Cold Kitchen and Tinhead show real catchments. That is careful siting and, in places, effective display.

There is no county recipe. The same method that lights up Adam’s Grave leaves South Street and Lanhill dark as silhouettes, and leaves West and East Kennet looking ordinary once you stop at the viewpoint that makes the postcard. Field, McOmish, Ruggles and Roberts already told us to expect local topography without a single bearing or a single display trick. The skyline scores say the same in a different dialect.

The two photographs at the top of this note are doing honest work. Figure 1 is what Kitchen’s southern catchment looks like from a real vale. Figure 2 is what West Kennet’s northern pocket looks like on a clear October afternoon. The maps are there so that neither picture has to carry a theory by itself.


Caveats (keep these next to the maps)

  • Bare-earth DTM — Environment Agency terrain without trees. Real woodland on approaches or crests would shrink catchments. Treat percentages as an upper bound.
  • Trees and chalk brightness — a fresh chalk mound would have been a louder signal than a green DTM bump; vegetation would have muffled it. Neither is modelled.
  • Chronology — Neolithic land cover and original mound height are not in the machine.
  • Nulls — raw skyline % on chalk scarps can flatter any high point. Contour-band and downslope checks matter when claiming “designed marker.”
  • Approach definition — results are conditional on the perp wedges and the 0.3–2.5 km band. A different sampling frame changes the percentages; the photo and pin ground truths remain valid for their viewpoints.
  • 20 m county DTM — fine for vale→ridge lines of sight; crest detail comes from the 1 m chips. Coarse cells near the crest can smear local ridge texture.
  • This is not a ridge-axis test and not a solstitial horizon-altitude protocol. Do not mix the three.

What we are not saying

We are not saying no long barrow was ever seen on a skyline. Some clearly were, and still are. Figures 1 and 2 are two of them.

We are not saying topography did not matter. We are saying skyline display from length-shows approaches mattered locally and variously, when it mattered at all.


Orientation / ridge companion: Do Wiltshire’s long barrows face the sun?

Compilation © Tim Daw / sarsen.org · CC BY-SA 4.0.
Photographs © Tim Daw.
NHLE © Historic England / OGL · EA LiDAR © Environment Agency / OGL.
Roberts et al. 2018, Internet Archaeology 47, CC BY.
HER seed: Wheatley recreation 10.5281/zenodo.11005373.

With thanks

Field, McOmish and Brown; Ruggles; Roberts and the Historic England Stonehenge landscape team; Wheatley; the Wiltshire and Swindon HER; Historic England NHLE; Environment Agency LiDAR. The mistakes are ours.