The Boles Barrow bluestone

This post is the companion to the short film The Boles Barrow bluestone: a 400 kg exotic in Salisbury Museum, the claim that it came from a long barrow older than Stonehenge, and why every link in that claim breaks.

An exotic, not an erratic

The stone at the British Museum, 2022 · T. Daw

The boulder is Preseli spotted dolerite (Thomas, in WAM 1924; Thorpe et al. 1991), now Salisbury Museum SBYWM:1934.68. On Salisbury Plain it is an exotic: a rock lying far from its geological source, however it got there. An erratic is an exotic moved by a natural agent, usually glacial ice; every erratic is an exotic, but not every exotic is an erratic. Whether this one is an erratic depends on how it reached the Plain, and the evidence for that is where it was first found: in a long barrow older than Stonehenge, or at Stonehenge itself.

Why it matters

Boles Barrow, Environment Agency LiDAR 1 m (2022), silver hillshade, low sun from the north-west · OGL v3.0

Boles (Bowls) Barrow, ST 94204 46771, is a long barrow 18.6 km west of Stonehenge. Five of its thirteen primary burials have been dated, the latest to 3760–3630 cal BC (Parker Pearson et al. 2015). Stonehenge's first bluestones were set up about 3000 BC. A bluestone buried in the barrow would put bluestone on the Plain centuries before Stonehenge, and since Thorpe et al. (1991) the stone has been cited as evidence that glaciers, not people, carried the bluestones east. In 2015 Parker Pearson and colleagues thought a Boles Barrow origin "highly probable"; in 2020 Parker Pearson and Richards concluded it "cannot be the Boles Barrow stone". The British Museum's 2022 label hedged: "Boles Barrow or Stonehenge".

The dig is in the archive

Colt Hoare, Ancient Wiltshire I (1812), Heytesbury Station III · photo T. Daw

William Cunnington opened the barrow in 1801. His letter to H. P. Wyndham of 18 July 1801, known from a copy in his daughter Elizabeth's hand, describes "a ridge of large stones and flints" over the burials; a footnote in his own hand gives their weight: "from about 28lbs. to 200 lbs." The letter calls them "of the same species of Stone as the very large Stones at Stonehenge … what the Country people call Sarsens". No bluestone is mentioned, and Colt Hoare's account (1812, pp. 87–88) has none either. The digs of 2023 and 2024 found no bluestone (The Past, 27 May 2023).

Too big

Salisbury Museum, 2012 · T. Daw

Wyndham, writing to Colt Hoare in 1802, described the same stones as "from 28lbs. to 200lbs. in weight", "similar in substance to many at Stonehenge and … often found peeping out from the turf or just under it, in the vallies of our downs like those near Abury". These are local sarsens of 13 to 91 kg. Published weights for the bluestone boulder run from 340 kg (Williams-Thorpe & Thorpe 1992) to 611.64 kg (Salisbury Museum label, 2012); the film says "around 400 kg".

An undated note

The only link is a second footnote in Cunnington's hand on the copy of the letter. As printed in 1924: "Since writing the above I discover among them the Blue hard Stone also, ye same to some of the upright Stones in ye inner Circle at Stonehenge." The first printing, in 1922, reads "I discovered amongst them the Blue hard Stone, ye same as the upright Stones in ye inner Circle at Stonehenge", and its editor, B. Howard Cunnington, thought it "possible that after the letter to Mr. Wyndham was sent, the foregoing note was added as a memorandum". A second copy of the letter carries the footnote mark but no note. The note gives no date and no size.

Matched in 1923

Salisbury Museum, 2016 · T. Daw

The boulder was connected to the note 122 years after the dig. In 1923 B. Howard Cunnington searched William Cunnington's old garden in Heytesbury and found three sarsens and a Dartmoor granite block, "but no 'Blue Stone'". Lord Heytesbury then found a bluestone under a beech tree at Heytesbury House. His aunt, the Hon. Mrs Hamersley, recalled that "the stone was removed from the late Mr. Wm. Cunnington's garden at Heytesbury to its present site at Heytesbury House before 1860. It was called the 'Stonehenge Stone'." On that account and Dr H. H. Thomas's identification of the rock, B. Howard Cunnington concluded that "there can be little doubt" it was the Boles Barrow stone, explaining its name as arising "from its similarity to the Blue Stones". An 1864 family letter records that another stone in the same garden had been wrongly "supposed … a stone brought from Stonehenge".

Where Colt Hoare did find bluestone

Colt Hoare (1812), p. 127

Colt Hoare did record bluestone when he found it. Amesbury No. 16, near Stonehenge, was "a mutilated flat barrow, 76 feet in diameter", a round barrow whose primary burial was a cremation in a cist with "a spear head of brass in fine preservation, and a pin of the same metal": a Bronze Age burial, later than Stonehenge. Over the cist "we found a large piece of one of the blue stones of STONEHENGE", which, he wrote, "decidedly proves that the adjoining temple was erected previous to the tumulus". On the same page he noted that the sarsen pieces in the barrow were "chipped off, (I am sorry to say) like those now daily knocked off from the great fallen trilithon".

Notes on the film

Every link between the boulder and Boles Barrow breaks: it was not recorded at the dig; it is several times heavier than the stones that were; the note that mentions a "Blue hard Stone" is undated and gives no size; and the boulder was matched to the note only in 1923, at another house, where it was known as the Stonehenge Stone. It is much more likely to have been obtained from Stonehenge, by whom and when is not known: it may have left the monument centuries before Cunnington, when stone was being taken from it. If so, it is no evidence for glacial transport of bluestones to Salisbury Plain. Accounts of its surface differ: "certainly has been dressed" (1924), "appears unworked" (1992), parts "worked down with metal tools" (Parker Pearson & Richards 2020). The note is quoted from its printed versions; the manuscript has not been re-examined. Photographs: T. Daw. Map: contains OS data © Crown copyright and database right 2026 (OS Terrain 50, Open Rivers, Open Names). LiDAR: contains Environment Agency data, © Environment Agency copyright and/or database right 2022, Open Government Licence v3.0. Music: original. Earlier posts: The Bowls Barrow Bluestone in Salisbury Museum (2012), The Bowls or Boles Barrow Bluestone – a Red Herring (2016), The Boles Barrow Bluestone (2022), Colt Hoare's description (2022), Did Cunnington find any bluestone in Boles Barrow? (2024).

Sources

British Museum 2022. The world of Stonehenge, exhibition label and large-print guide, p. 38.

Colt Hoare, R. 1812. The Ancient History of Wiltshire, vol. I, pp. 87–88, 127.

Cunnington, B. H. 1922. "Blue hard stone, ye same as at Stonehenge," found in Boles [Bowles] Barrow (Heytesbury, I.). Wiltshire Archaeological and Natural History Magazine 41, 172–174.

Cunnington, B. H. 1924. The "Blue Stone" from Boles Barrow. Wiltshire Archaeological and Natural History Magazine 42, 431–437.

Parker Pearson, M. et al. 2015. Antiquity 89.

Parker Pearson, M. and Richards, C. 2020. The Stonehenge bluestones. In M. Parker Pearson et al., Stonehenge for the Ancestors, Part 1. Leiden: Sidestone, p. 174. doi:10.59641/x8a4u5v6w7

The Past 2023. The latest from the past: Re-excavating Boles Barrow. 27 May. the-past.com

Thorpe, R. S. et al. 1991. Proceedings of the Prehistoric Society 57.

Williams-Thorpe, O. and Thorpe, R. S. 1992. Geochemistry, sources and transport of the Stonehenge bluestones. Proceedings of the British Academy 77, 133–161.

Is Stonehenge a henge?

"Did you know Stonehenge isn't actually a henge?" By the archaeological definition, that's correct. The more interesting question is where the word came from. This page is the companion to the short film Is Stonehenge a henge?

The definition

T. D. Kendrick coined "henge" in 1932 as a class name, taken from Stonehenge. As an archaeological type, a henge is a round earthwork "in which a ditch was dug to make a bank, which was thrown up on the outside edge of the ditch" (Pitts 2001, 26–28): ditch inside, bank outside. Stonehenge's own neighbours fit it. Durrington Walls is "surrounded by a ditch up to 17.6m wide and an outer bank", and Woodhenge has an outer bank "up to 10m wide" (Historic England, List entry 1009133).

Stonehenge reverses it. "The ditch of the enclosure is flanked on the inside by a high bank and on the outside by a low bank, or counterscarp" (Encyclopaedia Britannica). The monument that gave the class its name fails the class's test.

A henge: ditch inside, bank outside. Diagram, not to scale. 

Click pictures to embiggen

Stonehenge: main bank inside the ditch, low bank outside. Diagram, not to scale.

The name

The earliest record is Henry of Huntingdon's, c. 1130, listing the wonders of England: "Secundum est apud Stanenges; ubi lapides mirae magnitudinis in modum portarum elevati sunt, ita ut portae portis superpositae videantur". In translation: "The second is at Stanenges, where stones of wonderful size are raised like doorways, so that doorways seem set on doorways."

The usual reading splits the name into Old English stān, "stone", and hengen, "something hung": a gallows, or stones hung in the air. Stukeley (1740, ch. II) took both views: "Stonehenge is a stone gallows, called so from the hanging parts, architraves, or rather imposts", and "pendulous rocks are now called henges in Yorkshire… Stonehenge in Saxon signifies the hanging stones."

John Hines (2025) takes hengen in its dominant Old English sense. The Dictionary of Old English records one instance meaning "hanging"; the rest refer to "the cross or rack used for torture", and the word glosses ergastulum, a house of correction. He reads the name as "stone prison".

A hanger?

A third candidate is the downland word for a wood on a slope. Old English hangra is "a wood on a hill-side" (Bosworth–Toller), and it survives as hanger. Gilbert White's Selborne had "a long hanging wood called the Hanger. The covert of this eminence is altogether beech" (White 1789, Letter I). The same word gives Hanger Hill and Hanger Lane in Ealing. Related words across the North Sea mean "slope": Middle Low German hanc and Middle Dutch hangende.

The obvious objection is spelling. The early forms (Stanenges, Stanheng, Stanhenge) have no r. But Old English also had henge-clif, "a steep, precipitous cliff; præruptum" (Ælfric's Glossary; Bosworth–Toller), a henge- word for steep ground with no r at all.

Stonehenge sits on the brow of a gentle slope, with the hanger wood of Luxenborough plantation beside it. Read as a "stone hanger", the name describes where it stands, as the hanger woods of the Downs are named for where they grow (Daw 2016). That remains a suggestion. Hengen, in one sense or another, is the usual reading.

Stonehenge with the hanger wood behind.

Caveats

• "Henge" as a class is a 20th-century convention; the builders did not share it.
• The film's section diagrams are schematic and not to scale.
• The cognates come from Wiktionary's etymology for hangra and still need checking against a printed etymological dictionary.
• Music: original.

Sources

• Bosworth, J. & Toller, T. N. An Anglo-Saxon Dictionary: hangra; henge-clif.
• Henry of Huntingdon, Historia Anglorum (c. 1130). Latin as quoted in S. Ferguson, "On a passage in the Historia Anglorum of Henry of Huntingdon relative to Stonehenge", Proceedings of the Royal Irish Academy 9.
• Hines, J. 2025. Anglo-Saxon Stonehenge. Early Medieval England and its Neighbours 51. Cambridge Core
• Historic England, List entry 1009133: Henge monuments at Durrington Walls and Woodhenge.
• Kendrick, T. D. & Hawkes, C. F. C. 1932. Archaeology in England and Wales 1914–1931. London: Methuen.
• Pitts, M. 2001. Hengeworld. London: Arrow.
• Stukeley, W. 1740. Stonehenge, a Temple Restor'd to the British Druids. London.
• White, G. 1789. The Natural History and Antiquities of Selborne. London.
• Encyclopaedia Britannica, "Stonehenge".

Earlier post: Stonehenge – What does "Henge" mean, why is it a "Henge"? (9 December 2016)

The road under the rampart: a Roman road, Bokerley Dyke and Pitt-Rivers' Section 5

This post is the companion to the short film The road under the rampart. A recent claim holds that the Roman road across Cranborne Chase, locally called Ackling Dyke, began as a prehistoric route. Despite the name it is a road on a raised bank, not a boundary dyke; the dyke in this story is Bokerley Dyke, which cuts across it. The film tests that against the 1 m LiDAR and against the section General Pitt-Rivers cut where the road meets Bokerley Dyke in 1888–90. The evidence, with the quotations in full, follows.

The claim

In a series of 2026 posts on prehistoric-britain.co.uk, R. J. Langdon argues that Ackling Dyke, as the road is locally called, is "a multi-phase transport network rather than a single Roman construction", possibly a water-assisted corridor from a time of higher prehistoric water levels, which the Romans rebuilt and resurfaced. He accepts that "we cannot yet say that the earliest Ackling feature was definitely a prehistoric canal". The argument rests on changes in the size and form of the bank along its length, on its relation to palaeochannels and pits, and on a reading of Pitt-Rivers. A second post, on Puddletown Forest north-east of Dorchester, makes the general point that "metalling is a construction technique, not a chronological marker", and that "the Roman-road interpretation still needs proof".

The road on the downs

The road from Old Sarum to Badbury Rings runs on a raised bank, the agger, which the RCHME recorded as 40 to 50 ft wide and 4 to 6 ft high where best preserved (RCHME 1975). On the Environment Agency 1 m terrain model, north-east of the Dorset Cursus, the bank stands 0.4 to 1.25 m above the ground beside it along 93% of a 4.1 km trace.

The Roman road (Ackling Dyke) north-east of the Dorset Cursus. EA LIDAR Composite DTM 1 m, silver-sun shading. 

Click pictures to embiggen

The bank goes up and over the chalk. Traced along its crest from the point where it crosses the Dorset Cursus, it rises from 77.6 m OD to 115.4 m on Bottlebush Down within 1.1 km, falls to 87.1 m at 2.35 km and climbs again to 117.4 m at 4.1 km. A bank that rises and falls by 30 to 38 m across interfluves cannot have carried water along its length.

Crest of the road bank from the Dorset Cursus north-east for 4.1 km. Height exaggerated as marked.

The road is younger than the barrows it crosses. On Oakley Down the agger "cuts two disc barrows (Wimborne St. Giles (106) and (111)) on the edge of a large group there" (RCHME 1975). On the LiDAR the ring ditch of one stops at the bank, which runs on unbroken. That places the road after the Early Bronze Age, which is a weak bound on its own, but it is the clearest superposition visible from the air.

Oakley Down: the road bank and the edge of the barrow cemetery. Ringed: a disc barrow whose ditch stops at the bank.

Pitt-Rivers at Bokerley

Between 1888 and 1890 Pitt-Rivers cut a series of sections at Bokerly Junction, where the road meets Bokerley Dyke, and published them in the third volume of Excavations in Cranborne Chase (1892). The key to his plates states that "the position of each object was fixed with a spirit-level". He dated the dyke by the coins in and under it, and concluded that it was "thrown up no earlier than the reign of Honorius, a.d. 395-423" (p. 20).

View of Section 1, Bokerly Dyke, looking south-west towards Woodyates. Pitt-Rivers 1892, p. 73.

His Section 4 across the road, away from the Romano-British settlement at Woodyates, shows the road "in its most perfect state": six courses on the old ground surface, "(1) surface mould, 5 inches; (2), gravel with rounded pebbles … 6 inches; (3), rammed chalk rubble, 6 inches; (4), tertiary gravel again, 10 inches; (5), rammed chalk, 6 inches; (6), a single layer of nodular flints, laying on the old surface line. The total height from the old surface line, to the top of the road was 3 feet" (p. 74).

The six courses of Section 4. Diagram from Pitt-Rivers 1892, p. 74.

Section 3, beside the settlement, is different: "The fragments of New Forest ware, and of nails, and a glass bead in the bank of Section 3, shows that the ground must have been occupied to some extent before the road was made" (p. 74). New Forest ware is late Roman. On Pitt-Rivers' own reading, the road bank there was built, or rebuilt, late in the Roman period.

Section 5

Section 5 was cut "across Bokerly Fore and Rear Dykes, along the line of the centre of the Roman Road" (Plate CLXXI). Read from the bottom up:

1. An earlier line of the dyke, the Rear Dyke, was dug and then filled in. In the filling, below the road, lie a coin of Carausius (AD 287–293), a coin of Valens (AD 364–378) and red Samian ware.
2. "The lowest strata, consisting of a pavement of nodular flints, is shown overlaying the filling of the Rear Dyke behind" (p. 91). The road surface here was laid after AD 364. In Pitt-Rivers' words, this was "proving that the Roman Road was used after the Rear Dyke was filled in" (p. 21).
3. Above the road lies a layer of black mould with coins of Helena, Constantius II, Septimius Severus and Gratian (AD 375–383).
4. The later Fore Dyke, the second line of Bokerley Dyke, cut the road, and its rampart was thrown over the road's three lowest courses: "The Roman Road must have existed before the Dyke was made, and must have been cut through to form the ditch of the Dyke, and the earth thrown up over the road to form the rampart" (p. 70).

Section 5 across Bokerly Fore and Rear Dykes, along the line of the centre of the Roman road. Pitt-Rivers 1892, Plate CLXXI (University of Michigan copy).

Langdon quotes Pitt-Rivers' caution that "it does not follow that the Roman Road was made after the Rear Dyke was filled in, as it may have been dug across, and the road afterwards laid again over the filling of the ditch" (p. 21). In context the sentence allows the road to be older than the Rear Dyke, itself a late Roman work. It says nothing about a road before the Roman period.

The order of events

Pitt-Rivers called the two lines of Bokerley Dyke at the junction the Rear Dyke (the first) and the Fore Dyke (the later). Read from the oldest:

1. Bronze Age disc barrows on Oakley Down: the road bank cuts two of them (RCHME 1975).
2. The Roman road: built after the barrows; when is not tested by these sections.
3. The first line of Bokerley Dyke (Rear Dyke): dug and later filled in; the latest coin in the filling is of Valens, AD 364–378. Whether its ditch cut an existing road is left open by Pitt-Rivers ("it may have been dug across", p. 21).
4. The road resurfaced: its flints laid over the filled ditch, after AD 364.
5. The later line of Bokerley Dyke (Fore Dyke): its ditch cuts the road and its bank covers the road's lower courses; Pitt-Rivers dates the dyke no earlier than Honorius, AD 395–423 (p. 20).

The Dorset HER's later phasing of Bokerley Dyke (after Rahtz 1961) appears to describe the same sequence: a "B" Dyke, shortly after AD 364, "cuts through the Badbury–Old Sarum Road" and "the road was restored over it very soon afterwards"; a "C" Dyke, after AD 393–5, cut the road again, "and this time remained cut" (MDO5932).

Conclusion

Every dated relationship puts the road in the Roman period: it cuts Early Bronze Age barrows; beside the Woodyates settlement its bank contains late Roman pottery; at Bokerly Junction it was resurfaced across a ditch filled after AD 364 and then cut by a dyke later still. No dated layer places any phase of the road before Rome. The sections date the road's use and repair, not its first construction, and they come from the Bokerley end; the LiDAR trace covers 4.1 km of the downs. A prehistoric origin would need a dated deposit sealed beneath the primary agger. None has been reported.

Langdon is right that metalling alone dates nothing. Section 5 is the kind of evidence his argument asks for: road metalling with coins sealed beneath it. It answers for the Old Sarum–Badbury road at Bokerley. The stretch he examines in Puddletown Forest, on the road from Badbury Rings to Dorchester, has no dated finds in the Dorset HER (MDO47865): a section at Thorncombe Wood found gravel laid on the old ground surface, wheel ruts and no side ditches. There the road's date rests on its line and form, and dated sections would settle it.

Notes on the film. The LiDAR images use the Environment Agency LIDAR Composite DTM at 1 m (2022), shaded with a low north-west sun. The profile is traced along the crest of the bank on the same data. The diagrams of Section 5 and of the road's courses are redrawn and simplified from Pitt-Rivers' Plates CLXXI and CLXIII and p. 74, with heights exaggerated as marked. Plates from the University of Michigan copy of the 1892 volume. The code is in the film's folder on GitHub (make_assets.py). Music: original.

Sources

• Langdon, R. J. 2026. Ackling Dyke Part II: Puddletown Forest; Ackling Dyke at Woodyates: Part III; Ackling Dyke – Facts and the Archaeological Fiction. prehistoric-britain.co.uk.
• Pitt-Rivers, A. H. L. F. 1892. Excavations in Cranborne Chase, near Rushmore, on the borders of Dorset and Wilts, vol. III: Excavations in Bokerly and Wansdyke, Dorset and Wilts, 1888–1891. Privately printed. archive.org.
• Rahtz, P. A. 1961. Excavations on Bokerley Dyke in 1958, in advance of road widening. Archaeological Journal 118, 65–99 (as cited by the Dorset HER; title not checked).
• RCHME 1975. An Inventory of Historical Monuments in the County of Dorset, Volume V: East Dorset. HMSO.
• Dorset Historic Environment Record: MDO5932 Bokerley Dyke; MDO5591 Ackling Dyke, Gussage All Saints; MDO5640 Ackling Dyke, Gussage St Michael; MDO47865 Roman road from Badbury Rings to Dorchester.

LiDAR: Environment Agency LIDAR Composite DTM 1 m, 2022. © Environment Agency copyright and/or database right 2022. Open Government Licence v3.0.

Sea or land? Calculating the bluestone route

This post goes with the short film Sea or land? and with a model anyone can run in a browser:

Calculating the bluestone route. (click to go to the model)

The intro film on YouTube

In short

Did the bluestones travel from the Preseli hills to Stonehenge by sea or over land? The model weighs the hard parts of the journey: distance, hills, time on the water, and lifting stones of several tonnes into and out of boats. Each can be turned up or down. For every setting, the model searches the ground for the easiest route; no route is drawn in advance and then fitted to the settings.

• If boats are easy, the sea wins: down to Carmarthen Bay, then up the Bristol Channel to Avonmouth.
• If loading and landing are hard work, the land wins, along the line of today's A40 through Llandovery, Brecon and Monmouth. On the most reasonable settings, this is the answer.
• Many land routes are almost as easy, and all of them cross the Severn at one place: Newnham, below Gloucester.
• The two Preseli outcrops, one high on the ridge and one lower down, give the same answer almost every time.
• Keeping boats in sight of land, as Atkinson assumed, makes no difference.

None of this says where the stones actually went. Tides, weather, boats, crews and much else are left out. The model puts numbers on the argument, so that anyone can see what each assumption implies.

The question

Bluestone dolerites and rhyolites at Stonehenge have been matched to outcrops on the north side of Mynydd Preseli, among them Carn Goedog (Bevins, Ixer & Pearce 2014) and Craig Rhos-y-felin (Parker Pearson et al. 2015). Carn Goedog is 219 km from Stonehenge in a straight line. Proposed routes fall into two groups: by sea along the south Wales coast and up the Bristol Channel, as Atkinson proposed, or overland through south Wales and across the Severn. The overland case has been made here before, in The natural corridor for bluestones and Natural route analysis.

A least-cost model can compare the two only if water has a price. Make the sea free and the answer is the sea; make it a wall and the answer is the land. Published corridor work does the second: in Lewis (2024) the sea lies outside the cost surface. The question here is therefore: how cheap must water travel be, relative to hauling over land, before the cheapest route takes to the sea?

The model

The ground is OS Terrain 50, averaged onto a 200 m grid from Pembrokeshire to Hampshire and south to Land's End. Each step to a neighbouring cell is costed in metres of flat-ground hauling:

• Overland: distance, plus 4 × metres climbed, plus 2.6 × metres descended.
• On water: distance × m, the water cost. At m = 1 a kilometre on water costs the same as a kilometre on the flat; at 0.5, half as much.
• Loading: an optional fixed charge T each time the load goes onto or off the water.

The climb weight of 4 corresponds to hauling against a friction coefficient of 0.25: if the force required scales as μ + gradient, the cost per metre scales as 1 + gradient/μ. Sea is any cell where most Terrain 50 posts lie below 0 m OD or where there are no posts offshore. Dijkstra's algorithm finds the cheapest route. A route counts as seaborne when at least 25% of it is on water, and as overland when no more than 10% is.

The order of work matters. First the settings were fixed: two outcrops, thirteen water costs, four loading charges, three climb weights and three rules for keeping to the coast, 936 combinations in all (468 from each outcrop). Then, for each combination, the model searched the whole cost surface and kept the cheapest route it found. No route was chosen or drawn beforehand: each one is simply the output for its settings, and different settings often return the same route. Because the full set is too slow to run in a browser, it was run in advance, and the model page looks up the stored result for whatever settings are selected. Scripts and full results are in the project repository.

Several other settings were tested and left off the page because they barely move the result. A climb weight anywhere from 1 to 16 puts the sea–land switch at m = 1.01–1.12. Closing slopes steeper than 1 in 10, or treating the main rivers as barriers or as waterways, leaves it at 1.03. Grids of 400, 200 and 100 m give 1.027, 1.030 and 1.037. Allowing 16 moves per cell instead of 8 raises it to 1.05–1.08.

The cheapest route: the A40

The cheapest route with water at 1 × flat ground and a charge of 25 km of hauling for each loading and each landing: Llandovery, Brecon, Monmouth, round the head of the Severn estuary. Model run, 200 m grid.

The model page opens with water at the same cost as the flat, a charge of 25 km of hauling for each loading and each landing, the standard climb weight, and boats kept in sight of land. On these settings the cheapest route never touches water. It runs from Carn Goedog up the Tywi to Llandovery, on to Brecon and Monmouth, and round the head of the Severn estuary: 256.5 km, the line of the A40. For the sea to win, water must be about 20% cheaper per kilometre than the flat (the switch lies between m = 0.79 and 0.81).

The loading charge decides this. Lifting a stone of several tonnes onto a boat and off again is not free, and without a charge the model lets a load hop on and off the water at no cost. With the charge, the land route avoids even a short ferry across the Severn. The right size of charge is open. Of the 117 settings per outcrop at each charge, the A40 is the answer in 9 with no charge, 24 at 10 km, 66 at 25 km and 80 at 50 km.

One crossing

Ground lying on some route within 1% (dark red), 2% (orange) or 5% (yellow) of the cheapest, from Carn Goedog, on the model page's default settings.

A single cheapest line overstates what the ground decides. A better measure is the band of near-cheapest routes: every cell on some route costing no more than 1%, 2% or 5% above the cheapest. For a 256 km route, 1% is about 2.5 km of hauling.

On the default settings the 1% band is 15–20 km wide from Preseli to Brecon and splits round the hills into a Teifi side and a Tywi side. The ground does not pick one valley. It does pick one crossing: every near-cheapest land route crosses the Severn at Newnham, about 12 km below Gloucester, where on a 200 m grid the estuary has narrowed to river width. The model charges nothing for crossing a river, so this marks where the estuary stops being sea in the terrain data, not a known ford or ferry. The historic lowest bridge was at Gloucester. East of the Severn the band widens again towards Stonehenge.

Near-cheapest band with water at 2 × flat ground and no loading charge. Bands as above.

With water at twice the cost of the flat and no loading charge, the band runs straighter and funnels instead to the short crossing at Beachley–Aust. Either way the model identifies a crossing place, not a single line through Wales.

The sea's case

Share of the cheapest route on water as the water cost changes (Carn Goedog, 200 m grid, no loading charge). The route flips at m = 1.03.

Without a loading charge the balance is almost exactly even. The route switches from sea to land at m = 1.03 for both outcrops: the sea wins whenever a kilometre on water costs no more than about a kilometre on the flat.

The reason is geography. The Bristol Channel lies almost on the straight line from Preseli to Stonehenge, and at the switch the last sea route and the first land route are both 238.9 km long. Climbing adds about 2% to the sea route and about 9% to an all-land route, so the hills of south Wales hardly count. What decides the outcome is the cost of water relative to the flat, and a terrain model cannot supply that.

Water at half the cost of the flat, no loading charge: the route boards in Carmarthen Bay and lands at Avonmouth. Model run, 200 m grid.

With water at half the cost of the flat and no loading charge, the route from Carn Goedog walks 15–20 km to Carmarthen Bay, boards near Pendine, sails up the Bristol Channel and lands at Avonmouth: 259 km, 61% on water.

Water at twice the cost of the flat, no loading charge: the route walks and crosses the Severn at Beachley–Aust. Model run, 200 m grid.

At twice the cost it walks: up the Tywi, across the coalfield valleys towards Newport, over the shortest Severn crossing (3.5 km, Beachley to Aust) and on through Bath: 238 km, 1.5% on water. That route holds up to water at ten times the cost of the flat. The A40 line takes over only when loading is charged or water is very dear.

Two outcrops

Carn Goedog sits on the ridge at about 290 m OD, 9 km from the sea at Newport Bay. Craig Rhos-y-felin lies in the valley below at about 80 m, 6 km from the same bay. Across 468 combinations of settings the two agree on sea or land in all but two, and the switch is the same. They differ when water is cheap. At a fifth of the cost of the flat, the route from Craig Rhos-y-felin goes north to Newport Bay and round St David's Head (345 km), while the route from Carn Goedog walks south to Carmarthen Bay (260 km). Over the whole set, Craig Rhos-y-felin goes round the north 100 times and Carn Goedog 80.

Keeping to the coast

Atkinson's sea route assumed boats kept close inshore, in sight of land. The model tests this by closing sea cells. Under the in-sight rule a sea cell stays open only if land shows above the horizon from a boat with an eye height of 2 m, that is, within 3.57 × (√2 + √H) km of land H metres high. A stricter rule closes all sea more than 2 km from land.

Staying in sight of land changes nothing: from every stretch of sea these routes use, land is above the horizon, even round Land's End. Limits of 20 and 10 km also leave the switch unchanged, and 5 km moves it slightly, only with a loading charge (to 0.77–0.78). The 2 km limit lowers it to 0.94–0.97 without a charge and 0.67–0.68 with one, because a voyage hugging the shore is longer. In the Bristol Channel land is never far away, so keeping to the coast hardly affects the choice.

Round Land's End?

With the whole coast open, a route north to Newport Bay and round St David's Head and Land's End wins only when water costs about a tenth of the flat or less. At a twentieth it sails 685 km and lands at Southampton Water. Within 2 km of land it is never the cheapest route.

What the model leaves out

• Tides, currents, weather, seasons, and the risk of losing a stone at sea or on land.
• How the stones were moved: no boats, rafts, sledges, rollers or crew sizes are modelled.
• Vegetation, woodland and wetland. OS Terrain 50 is today's land surface.
• Soft or flooded valley floors, and the cost of crossing rivers. Valleys still attract routes because they are flat: 15.6% of the default land route lies in the main river corridors, which cover 2.2% of the land in the frame.
• Mid-Holocene sea level. By then relative sea level around the Bristol Channel was within a few metres of today's (Shennan, Bradley & Edwards 2018), not tens of metres lower as in the early Holocene. Most of these coasts are steep, so a few metres barely moves the shoreline on a 200 m grid. The Severn levels near Avonmouth and Weston-super-Mare are the exception, where the tidal edge may have lain some way inland. That changes where a stone could come ashore, not whether water beats land.
• Any claim that the cheapest route is the one used.

What follows

Once loading and landing cost something, the cheapest way from Preseli to Stonehenge is overland on the A40 line, through a broad band across Wales and a single crossing of the Severn at Newnham. Without that cost the ground cannot choose: sea and land routes are almost the same length, and the break-even sits at water costing about the same as the flat. Whether Neolithic water transport of a multi-tonne stone, loading and landing included, was cheaper than that is a question for experiment and for the archaeology of boats and landing places, not for elevation data. The model makes the price explicit and lets anyone change it: try the model.

Notes on the film

Every route in the film is a model run on the 200 m grid with 8 moves per cell, drawn as the model gives it, over an OS Terrain 50 hillshade. The near-cheapest band uses the model page's default settings. The switch chart shows the share of each cheapest route on water for 22 water costs. In the film, "boat 2× easier" means m = 0.5, "same effort" means m = 1, and "if loading boats is hard" means a charge of 25 km of hauling for each loading and each landing. The music is original, generated for the film.

Sources

• Bevins, R.E., Ixer, R.A. & Pearce, N.J.G. (2014). Carn Goedog is the likely major source of Stonehenge doleritic bluestones: evidence based on compatible element geochemistry and principal component analysis. Journal of Archaeological Science 42, 179–193. doi:10.1016/j.jas.2013.11.009
• Daw, T. (2024). The natural corridor for bluestones. sarsen.org.
• Daw, T. (2025). Natural route analysis of possible bluestone routes. sarsen.org.
• Daw, T. (2026). Calculating the bluestone route: scripts, results and method review. GitHub. Model page: timdaw37.github.io/bluestone-sea-dial.
• Lewis, J. (2024). Estimating the scale-dependent influence of natural terrestrial corridors on the positioning of settlements: a multi-scale study of Roman forts in Wales. Journal of Archaeological Science 170, 106055. doi:10.1016/j.jas.2024.106055
• Ordnance Survey. OS Terrain 50 and OS Open Rivers. Open Government Licence v3.0. Contains OS data © Crown copyright and database right 2026.
• Parker Pearson, M. et al. (2015). Craig Rhos-y-felin: a Welsh bluestone megalith quarry for Stonehenge. Antiquity 89, 1331–1352. doi:10.15184/aqy.2015.177
• Shennan, I., Bradley, S.L. & Edwards, R. (2018). Relative sea-level changes and crustal movements in Britain and Ireland since the Last Glacial Maximum. Quaternary Science Reviews 188, 143–159. doi:10.1016/j.quascirev.2018.03.031

Aurochs and Aurochsen - a short cartoon reminder

Stones followed people

The previous post (Metal Followed People?) found that Britain's Beaker-period incomers came from the Rhine while its first copper came up the Atlantic. A new preprint (McColl, Schulz Paulsson et al. 2026) asks the same question two thousand years earlier, of megaliths. It models the ancestry of 2,963 ancient Europeans, including 46 new genomes from megalithic and related burials in Portugal and Sardinia, against the radiocarbon chronology for megalith emergence. The test is simple: if megaliths spread with migrants, their appearance in a region should coincide with an influx of ancestry from a region already building them.

Click to enlarge

Britain: the monuments came with the people

Northern France, where the earliest megaliths appear around 4750 BC, carried a distinctive admixed ancestry, mostly of Western Mediterranean (Cardial) origin with a minor Central European (LBK) component. Every Neolithic individual sampled from Britain and Ireland models as that northern French ancestry plus a little local hunter-gatherer input, with almost none of the Iberian Cardial signal. The migration dates to about 4150–4050 BC and megaliths follow by about 3950 BC. Of the regions tested, only Britain and Ireland meet the migration expectation. The precise source remains open: no genomes survive from Brittany between about 4950 and 3850 BC. The earthen Passy monuments of the Paris Basin, built by people of the same ancestry from about 4750 BC, make the British earthen long barrow a plausible inheritance rather than a stoneless substitute.

Elsewhere, the monuments travelled without them

Western Iberia acquired passage graves indistinguishable from Britain's at the same date, yet the new Portuguese megalith burials are of local Iberian ancestry, with no rise in the northern French component in either phase of expansion. In Scandinavia, farmers carrying northern French–derived ancestry arrived around 4100 BC, but dolmens appear only around 3650 BC and passage graves around 3400 BC, with no fresh influx to account for the timing. The authors argue that building knowledge cannot have lain dormant for centuries and propose transmission by specialist builders moving through exchange networks. That argument overlooks the earthen long barrows built from early in the Danish and north German Funnel Beaker sequence. A local translation of an existing monument form into stone fits the delay equally well.

Jadeite as the network

Alpine jadeitite plays the part that copper plays in the Beaker story. From about 4750 BC it reached Brittany, which became a redistribution centre feeding Iberia. Quarrying in the western Alps had largely ceased by about 4350 BC, yet jadeitite axes reached the British Isles and southern Scandinavia from about 4150 BC and remained in circulation until about 3550 BC. Megaliths emerged only within the reach of these networks, and only among populations of Cardial-derived ancestry, never among persisting hunter-gatherers or LBK descendants.

The inversion

Britain's two transitions share a structure. Around 4000 BC people and monuments arrived from northern France while prestige stone came through a separate network. Around 2450 BC people arrived from the Rhine while copper came up the Atlantic. In both, Iberia sent materials north (variscite and fibrolite then, copper later) without sending a detectable population. The cross-tabulation proposed for Beaker metal, grave goods against the ancestry of the buried, has now been done for megaliths: in Iberia the monument tradition crossed the ancestry divide.

Caveats

The paper is a preprint. Its northern French reference population is two Cerny individuals from the region where megaliths began, which builds part of the association into the design. The survival model linking ancestry to megalith emergence rests on six regional events. A handful of incoming specialists would be invisible to genome-wide ancestry modelling, so "no migration" in Iberia means none detectable.

Sources
McColl H, Schulz Paulsson B, Shennan S, et al. 2026. Migrations facilitated the cultural diffusion of megaliths in Neolithic Europe. bioRxiv preprint, posted 1 October 2026. doi:10.64898/2026.09.24.753699
Merkel SW, Arnoldussen S, Theunissen L, et al. 2026. Tracking Europe-wide copper and bronze flow in the Dutch Late Neolithic to the Early Iron Age. PLOS One 21(9): e0348751. doi:10.1371/journal.pone.0348751
Olalde I, Brace S, Allentoft ME, et al. 2018. The Beaker phenomenon and the genomic transformation of northwest Europe. Nature 555: 190–196. doi:10.1038/nature25738

Where would the aurochs drink? Herds, springs and the Stonehenge car-park posts

What we know

Blick Mead, east of Stonehenge, is a chalk spring where Mesolithic people hunted aurochsen and came back for a very long time (see Buried Landscapes of the Avon). On the ridge to the west are the big Mesolithic posts found under the old car park. Five radiocarbon dates on their pine charcoal span about 8820–6590 cal BC (Allen & Bayliss 1995, in Bronk Ramsey & Bayliss). Nearby runs the palisade ditch, which is poorly dated. It is put in the Late Neolithic on archaeological grounds, perhaps 2900–2400 BC, and the only date is from an Iron Age burial cut into it, 780–410 cal BC (Lawson 1997; Bronk Ramsey & Bayliss). The posts and the palisade are something like 4,000 to 6,000 years apart. I have suggested that the posts held machans, raised hunting platforms like those E. P. Stebbing drew in India. I have also wondered whether a palisade with gaps worked like a bull-run fence. Both ideas need herds to pass by.

So where would herds actually walk to water? On the chalk, the answer depends on winter. The climate of the period was much like today's, and the Avon gets frosty in a cold spell but doesn't freeze solid (see Britain, 5000–2000 BC: no ice, no catastrophe, a familiar climate). A spring, meanwhile, stays open. So the model below gives open springs an advantage in frost: a herd will walk 0.5, 1 or 2 km further to reach one.

How cattle walk

The rules come from studies of domestic cattle, not aurochsen, but they are the best measurements there are.

• Climbing is costly. On a treadmill, cattle used about 26 J per kg for each metre climbed, against 2 J per kg per metre on the flat (Ribeiro et al. 1977). So a metre of climb costs as much as about 13 metres on the level.
• Going down costs too. Steers walking down a 6% grade used about as much energy as walking up it (Di Marco & Aello 1998).
• Steep ground is avoided. Cattle start avoiding slopes of 20% (Ganskopp & Vavra 1987). Land over 60% is treated as ungrazable (Holechek 1988), and the model treats it as impassable.
• Distance from water matters. The rangeland rule of thumb is full use up to 1.6 km from water and half use from 1.6 to 3.2 km (Holechek 1988). GPS-collared cattle often go further than that (Millward et al. 2020).
• Trails find the easy line. Real cattle trails from water were 11% shorter than GIS least-effort paths. They ran on slopes of 5.2% across pastures that averaged 13.5% (Ganskopp et al. 2000).

The model puts these rules on Environment Agency LiDAR at 5 m resolution. It starts 2,145 herds on the high ground, one every 250 m wherever the ground is at least 25 m above a river. Each herd takes the cheapest route to water. The water is the Avon, the Till, Blick Mead, and five springs marked on the 1880s OS six-inch maps: four at Winterbourne Stoke and one at Durrington. Where many routes share a line, that is a busy track.

Results

The posts are not on a track. In every run, no busy route (one used by 25 or more herds) reaches them. In the hardest frost the closest busy route comes within 615–730 m of the posts when Blick Mead is the only spring (Figure 1). With the OS springs added (Figure 2), the closest is about 1.3 km away (1.28–1.39 km).

They sit on the edge of Blick Mead's winter catchment. With no advantage for springs, the ground around the posts drains to the lower Avon. Give the springs the smallest advantage tested, 0.5 km, and the same ground switches to Blick Mead. It stays with Blick Mead at every frost setting, with or without the other springs. The posts look more like a watch point over herds drifting towards the spring in winter than an ambush on a path.

Figure 1. Cattle walking rules in a hard frost (open springs worth a 2 km detour; Blick Mead the only spring). Purple marks the ground whose herds drink at Blick Mead: 463 of 2,145 herds, from 37.7 km². The busy routes converge on the spring but pass the posts at a distance.

Blick Mead is not the only draw. In the hardest frost tested, with all six springs, Blick Mead takes 328 herds from 27.9 km², the most for any single spring. The Winterbourne Stoke springs take 268, 261, 52 and 34, so 615 between them, and Durrington takes 182. In milder frost a Winterbourne Stoke spring beats Blick Mead: 142 herds to 90 at 0.5 km, and 185 to 128 at 1 km. Blick Mead is the busiest spring only at the hardest setting. Even so, the posts stay in its catchment.

Figure 2. The same hard frost with the five springs from the 1880s OS six-inch maps added (green dots; red marks herds going to those springs). The Winterbourne Stoke group takes much of the Till side, but the posts remain in Blick Mead's catchment (purple).

The palisade is not a funnel. Few routes come near it. Making it a solid barrier changes almost nothing: in any run, at most one of the 2,145 routes changes its water. If it steered animals, it was in a drive, which this model cannot test.

Limits

This is a simple exploratory model, not proof. There are no GPS tracks to test it against. The rules come from cattle, and bison, the nearest wild comparison, avoid slopes more strongly and are less tied to water (Allred et al. 2011). The rivers are today's, from OpenStreetMap. The springs are Victorian map labels placed to within ±40–60 m. The posts and the palisade are thousands of years apart, so the model puts them on one landscape only for comparison. Some settings are my own choices, such as the steepness penalty reaching ×10 at a 60% slope.

GPS tracks of cattle grazing chalk downland for conservation would be the real test.

References

• Allred, B.W., Fuhlendorf, S.D. & Hamilton, R.G. (2011). The role of herbivores in Great Plains conservation: comparative ecology of bison and cattle. Ecosphere 2(3): art26. https://doi.org/10.1890/ES10-00152.1
• Bronk Ramsey, C. & Bayliss, A. Dating Stonehenge. CAA conference proceedings, ch. 5 (reporting Allen, M.J. & Bayliss, A. 1995, Appendix 2: the radiocarbon dating programme, in Cleal, Walker & Montague 1995, Stonehenge in its Landscape, pp. 511–35). https://proceedings.caaconference.org/files/1996/05_Ramsey_Bayliss_CAA_1996.pdf
• Di Marco, O.N. & Aello, M.S. (1998). Energy cost of cattle walking on the level and on a gradient. Journal of Range Management 51: 9–13. https://doi.org/10.2307/4003556
• Ganskopp, D., Cruz, R. & Johnson, D.E. (2000). Least-effort pathways?: a GIS analysis of livestock trails in rugged terrain. Applied Animal Behaviour Science 68: 179–190. https://doi.org/10.1016/S0168-1591(00)00101-5
• Ganskopp, D. & Vavra, M. (1987). Slope use by cattle, feral horses, deer, and bighorn sheep. Northwest Science 61: 74–81. https://hdl.handle.net/2376/1753
• Holechek, J.L. (1988). An approach for setting the stocking rate. Rangelands 10(1): 10–14. http://hdl.handle.net/10150/640265
• Lawson, A.J. (1997). The structural history of Stonehenge. Proceedings of the British Academy 92: 15–37. https://www.thebritishacademy.ac.uk/documents/3913/92p015.pdf
• Millward, M.F., Bailey, D.W., Cibils, A.F. & Holechek, J.L. (2020). A GPS-based evaluation of factors commonly used to adjust cattle stocking rates on both extensive and mountainous rangelands. Rangelands 42: 63–71. https://doi.org/10.1016/j.rala.2020.04.001
• Ribeiro, J.M.deC.R., Brockway, J.M. & Webster, A.J.F. (1977). A note on the energy cost of walking in cattle. Animal Production 25: 107–110. https://doi.org/10.1017/S0003356100039118

Data: EA LiDAR Composite DTM 1 m © Environment Agency (OGL v3). Palisade ditch (HE_UID 219850) and Avenue from Historic England Aerial Investigation & Mapping, © Historic England (OGL v3). Rivers and the Blick Mead point © OpenStreetMap contributors (ODbL). Springs from the OS six-inch maps, reproduced with the permission of the National Library of Scotland, and GB1900 (CC BY-SA). Car-park post positions after Vatcher & Vatcher 1973 and Allen 1995 (HE Monument 219856).