Make your own LiDAR Lens

You do not need to be a programmer. An AI helper does the technical work; you make a few choices and open one free account.

What you get

A LiDAR Lens is a free map in your browser that takes away the trees and crops, so the shape of the ground shows: old banks, barrows, field systems, hollow ways. Drag a circular lens over an old Ordnance Survey map and the bare ground appears inside it. Turn the sun, change how the ground is drawn, and tap a spot to see what is recorded there. It works on a phone.

There is one for Wiltshire. On 21 October 2026 an AI helper built another, for the henges of the Ure and Swale valleys in North Yorkshire: 700 km² from the Thornborough henges to the Devil's Arrows, in about an hour, from the idea alone.

Four steps

1. Get an AI helper that can do work on a computer for you, not just chat. Claude and Grok have both built a Lens. For most people the paid AI plan is the only cost.
2. Give it one message. Copy the message below, change the area to yours, and send it.
3. Make a few choices. It may ask you, or choose for you: which area, whether the map is open to everyone or behind a password, and which old maps go underneath.
4. Open one free account. To put your map online it will ask you to open a Cloudflare account. Cloudflare asks for a card when you switch on its storage, but a county-sized map fits in the free allowance.

Then let it work. The 700 km² Ure map took about an hour. A whole county takes longer: most of a day, mostly unattended. Start with something small, such as your parish or a valley.

The message to copy

Please read the instructions at https://github.com/TimDaw37/lidar-lens and build me a LiDAR Lens for [your area]. I am not a programmer: explain each step in plain English, and ask me before anything that costs money or needs an account.

For your AI helper: the build guide is PROTOCOL.md in the lidar-lens code (MIT licence). Configs for Wiltshire and a blank template are in configs/. Use open data only and keep showGuess:false on a public site.

What it costs

• The AI helper: a paid plan. Prices vary and change.
• Cloudflare (putting the map online): usually nothing. The free allowance is 10 GB of storage (a county takes about 3–4 GB) and 100,000 requests a day, plenty for a club, a society or a village. A busy public map might need the paid plan, about $5 a month.
• Your computer: nothing extra, but a whole county needs about 30 GB of free space and a good connection. Some of the work can be done on the AI's own computer instead.
• The LiDAR and the old maps: free (Environment Agency, Open Government Licence; National Library of Scotland, CC-BY).

Not in England?

The Environment Agency's 1 m LiDAR covers England. Wales has its own free LiDAR from Natural Resources Wales (DataMapWales), and Scotland from the Scottish Remote Sensing Portal. The build guide says how to use them.

Two rules

• Open records only. National records from Historic England and OpenStreetMap are open. Your county's own Historic Environment Record is not: it needs the county's permission before any of it goes on a public map. Linking to it is fine.
• Report, don't publish. If you spot something new, tell your county's Historic Environment Record. Don't post maps of possible new sites: they help illegal metal detectorists. Most land is private, and scheduled monuments are protected by law.

Have a go

If it gets stuck, tell it what went wrong and let it try again. Start small, and share the link when it works.

Sources

• LiDAR Lens code and build guide: github.com/TimDaw37/lidar-lens (MIT licence).
• Environment Agency, LIDAR Composite DTM 1 m (Open Government Licence).
• Cloudflare, R2 pricing and Workers pricing, checked 21 October 2026.
• National Library of Scotland georeferenced OS maps (CC-BY).
• The same guide on GitHub: READ-ME-FIRST.

A LiDAR Lens for the Ure henges: Thornborough to the Devil's Arrows

 

After the Wiltshire LiDAR Lens, I wanted to look at the other great henge landscape, in North Yorkshire. So there is now a second one, free and with no login: the LiDAR Lens for the Ure henges.

What it covers

It uses the Environment Agency's 1 m LiDAR composite terrain model for a strip about 19 km by 37 km (703 km²), from Scorton and Catterick in the north down to the Devil's Arrows at Boroughbridge. The sites include:

• the three Thornborough henges
• the Nunwick, Hutton Moor, Cana Barn and Sinderby henges
• the Devil's Arrows
• Catterick and the Scorton cursus

One to look at is Langthorpe, just north-west of the Devil's Arrows. YAAM has drawn attention to earthworks there as a possible "super-enclosure". Their age and purpose are unknown. I have marked the spot where I think it shows in the LiDAR: see the Langthorpe view and judge for yourself.

How to use it

A circular lens sits on the aerial photo. Drag it about and resize it to see the bare ground underneath, drawn as hillshade, slope, local relief, sky-view factor or red relief. Low sun and some vertical exaggeration bring out the faint banks and ditches.

Click "What’s here?" and then a spot. The panel gives plain measurements of the ground there and lists nearby recorded sites, with links to the records. It does not guess what a feature is. That is left to you.

Credits

• LiDAR: Environment Agency, Open Government Licence
• Recorded sites: Historic England open data (scheduled monuments, listed buildings, aerial investigation mapping), Open Government Licence
• Map data © OpenStreetMap contributors
• Historic maps: reproduced with the permission of the National Library of Scotland, CC-BY

There is no North Yorkshire HER data in it. Instead, the "What’s here?" card links out to Heritage Gateway for the spot you clicked. Please respect landowners, and remember that scheduled monuments are protected by law.

The code is on GitHub if you would like to build one for your own patch. A non-programmers guide of how to is at : https://github.com/TimDaw37/lidar-lens/blob/main/READ-ME-FIRST.md 

Comments and anything interesting you spot are welcome below.

The largest henge in the world?

This post is the companion to the short film The largest henge in the world?, which revisits a post from October 2016 with fresh LiDAR. The measurements, sources and caveats follow.

The earthwork

In west Wiltshire, on private farmland with no public footpath, a bank and ditch enclose two ploughed fields beside a chalk river. Trees grow along most of the bank, so from the air it looks like a ring of woodland round the fields. The interior is ploughed out, but under the trees the bank and ditch are still impressive. In April 2016 I walked round it; the photographs here are from that walk.

Environment Agency first-return LiDAR: the trees on the bank.

The ditch in woodland, April 2016.

How big?

Traced along the outer edge of the bank on the Environment Agency's LIDAR Composite DTM at 1 m (2022), the earthwork encloses 23.2 ha, with a perimeter of 1.83 km and an extent of 640 × 530 m. A trace along the inner edge of the bank would give about 2–3 ha less. Earlier figures agree: Colt Hoare (1821) gave "an area of fifty acres" (20 ha), Robinson (1987) 54 acres (22 ha), Papworth (2012) 22 ha, and the 2016 post 23 ha.

For comparison, Historic England gives Durrington Walls "a roughly circular area of 19ha", c. 490 m north–south by 468 m east–west (list entry 1009133), and Marden "an irregular area of approximately 15ha", a maximum of 530 by 360 m (list entry 1014617). Both are overall figures, so the outer-edge measurement is the like-for-like one. In the film the two are drawn as ovals of those published dimensions, not as traced outlines.

Same scale: the traced earthwork (red) with ovals of the published sizes of Durrington Walls (gold) and Marden (blue).

The ditch is inside the bank

A henge is defined by its ditch lying inside its bank, the reverse of a defended enclosure. Height profiles across the earthwork on the LiDAR show the same pattern on the west, south and east sides: an outer slope, the bank, then a hollow on the inner side where the ditch has silted up, before the level interior. On the west side the bank stands about 3 m above the ground outside and the silted ditch lies about 0.6 m below the interior. On the north the earthwork follows the edge of the river terrace, which falls about 10 m to the floodplain; there the river forms part of the boundary, as the Avon does at Marden, where "the fourth side of the enclosure is formed by the edge of the floodplain" (Historic England 1014617). A few small quarries cut into the ditch. On the east side the reading is less secure: a track to the neighbouring house, in use from at least the 1880s to the 1920s, was cut into the inner face of the bank there (Papworth 2012), and the hollow on the LiDAR may be the track rather than the ditch. The west and south sides carry no such complication.

Bare-earth LiDAR, lit from the north-north-east for relief.

Profile across the west side, from the LiDAR. Diagram, height ×10.

What it has been called

The Wiltshire and Swindon Historic Environment Record lists it as a Romano-British settlement (MWI1116). Sir Richard Colt Hoare took it for a Roman station:

"...we discovered the grand and evident remains of a large Roman station, surrounded by an earthen vallum, and comprehending an area of fifty acres; in every part of which we dug up large fragments of Roman pottery of every species and colour... On digging into the soil, we found it to be of a black nature to a greater depth than usual, which I consider to be a certain sign of long residence and cultivation." (Hoare 1821, quoted by Papworth 2012, 240)

In about 1792 two labourers levelling "a high ridge", perhaps the bank, and digging a ditch found iron "armour", much Roman pottery and two or three large pots full of coins. The accounts conflict, but the earliest lists nothing later than about AD 285, and the hoard may have held in the region of 33,500 coins, one of the largest from Roman Britain (Robinson 1987). In 1868 drain-diggers found a pit about 7 m across holding "about 2 tons of large stones" with animal bones, pottery, coins and nails (Papworth 2012). Thirteen coins and a New Forest ware thumb pot are in Salisbury Museum. When the Ordnance Survey visited in 1966 they favoured a medieval enclosure.

Roman finds show that the place was used in the Roman period. They do not date the bank.

The 2010 trench

The one excavation was published by Martin Papworth in 2012. In 2006 resistivity and magnetometer survey of an 80 m square in the south-east corner of the interior showed rectilinear ditches and two spreads of rubble, perhaps buildings, with Roman pottery in the ploughsoil and nothing identifiably prehistoric. In May 2010, to test whether the earthwork was a Late Iron Age valley fort, a trench 25 m × 1.2 m was cut across the bank at the east corner and out over the ground where an outer ditch was expected.

There was no outer ditch. Neither the trench nor the geophysics found one. The bank survived as a clay deposit 0.2 m deep, without finds, sealed by layers of 16th- to 19th-century pottery and clay pipe; the lowest layer on the outer slope held a few small, abraded Romano-British sherds. No prehistoric artefacts were found, only a few flints that may have been struck. The bank had been levelled before the 19th century. Papworth concluded that the excavation "failed to date the enclosure" and found no evidence that the earthwork is prehistoric, and that a Roman date, resting on abraded sherds not from the bank itself, is "insecure".

Two points bear on the henge reading. The trench ran outward from the bank and stopped at the field boundary on its inner side, so it did not reach the inner ditch that the LiDAR shows elsewhere. And an enclosure with no ditch outside its bank is what a henge predicts and a defended enclosure, a valley fort, does not. The trench neither confirms nor refutes a henge; it removes the Iron Age fort as the obvious alternative.

A henge

David Field and David McOmish, in Neolithic Horizons (2016), and I read it as a henge, probably of a similar date to Marden. It has never been dated. Until it is, the henge reading rests on its form: a very large enclosure, ditch inside bank, with a river along one side.

Notes on the film

• "The largest henge in the world" is a deliberate flourish. Henges are almost unknown outside Britain and Ireland, so the title is easily won; the real comparison is with Durrington Walls and Marden.
• All LiDAR images are from the Environment Agency's LIDAR Composite DTM and First Return DSM at 1 m, under the Open Government Licence. Relief is shaded with the sun moved for clarity; the section diagram exaggerates height ×10.
• The trace of the earthwork is by eye on a hillshade (27 points).

Sources

• Field, D. and McOmish, D. 2016. Neolithic Horizons: Monuments and Changing Communities in the Wessex Landscape. Stroud: Fonthill.
• Historic England. List entry 1009133, Durrington Walls; list entry 1014617, The Hatfield Earthwork, Marden.
• Hoare, R. C. 1821. The Ancient History of Wiltshire, vol. II. London: W. Miller.
• Papworth, M. 2012. Note in Wiltshire Archaeological and Natural History Magazine 105, 240–2.
• Robinson, P. 1987. Note in Wiltshire Archaeological and Natural History Magazine 81, 130–2.
• Wiltshire and Swindon Historic Environment Record, MWI1116.
• Environment Agency. LIDAR Composite DTM 1 m and First Return DSM 1 m. Open Government Licence.

Historic Wales: a first look at the new map portal for Welsh heritage

 

I spend most of my time peering at Wiltshire, at sarsens, long barrows and LiDAR hillshades, so it's good to look over the border now and then and see how our Welsh neighbours do things. The new Historic Wales portal is in public beta until 1 December 2026, and its team is asking for feedback. So I've had a good look round.

What it is and who's behind it

Historic Wales calls itself "the map enabled portal for historic environment information in Wales". It's run by the Royal Commission on the Ancient and Historical Monuments of Wales (RCAHMW) and built on Esri's ArcGIS Hub and Experience Builder. What makes it worth having is that it brings the main Welsh heritage datasets together in one map:

• Cadw (cadw.gov.wales): Scheduled Monuments (I counted 4,236 records), Listed Buildings, Registered Historic Parks & Gardens and Designated Wrecks.
• Heneb (heneb.org.uk), the new body that now runs the regional Historic Environment Records: the HER of Wales, a huge 271,366 points, each linking to its Archwilio record.
• RCAHMW: the National Monuments Record of Wales, split into terrestrial and maritime layers, with each point linking to Coflein.

Think of it as Wales's answer to England's Heritage Gateway and Historic England's National Heritage List map, but on one map. That's the bit I envy. In Wiltshire I have the scheduling on one site, the HER on another and the old maps on a third.

The historic maps are the real treat

The highlight for me is the "Historic Mapping" theme. RCAHMW is working with regional archives and the National Library of Wales to digitise and georeference historic maps, and the beta already includes:

• Enclosure maps, funded by the Welsh Government. Breconshire, Carmarthenshire, Denbighshire, Flintshire, Glamorgan, Monmouthshire, Montgomeryshire and Pembrokeshire are already in, with the rest promised. You can lay Brecon Forest in 1819 or Malltraeth Marsh in 1861 straight over today's map.
• Admiralty charts from the UK Hydrographic Office, covering Milford Haven in 1830, the Swellies in 1872, Holyhead harbour and dozens more. Together they make up a new Maritime map.
• 6-inch Ordnance Survey maps from 1868 to 1892, courtesy of the National Library of Scotland, plus a promise of the 25-inch first edition. Anglesey and Flintshire are said to be online already.
• Historic county and civil parish boundaries for 1860–89 and 1889–1906. They're really handy, because so many old records are filed by the pre-1974 counties.

One tip, because it caught me (and others) out: ticking "Historic Mapping" on its own shows nothing. Every map sheet starts switched off, so expand the group, then the county or chart set, and tick an individual sheet. Each one only covers its own patch, so zoom to it. Once you know that, it all works nicely. The 1880s 6-inch sheet around Pentre Ifan is crisp right down to field level.

There's a swipe tool for comparing old and new maps, a measure tool, a choice of basemaps, layer reordering and transparency, and a table view. Each historic county also has its own preset map.

Trying it on two old favourites

Naturally I went straight for Pentre Ifan and Bryn Celli Ddu. Both turn up in all three datasets:

• Pentre Ifan Chambered Tomb is scheduled as PE008, with a separate scheduling, PE504, for the standing stone 120 m SSW. It's also in the HER (Dyfed records such as DAT1471) and in Coflein as NPRN 101450.
• Bryn Celli Ddu is AN002 to Cadw, GAT2694 in the HER and NPRN 93827 in Coflein. Around it sit a plough-levelled cairn, a cup-marked outcrop and an enclosure to the south-west. That's exactly the sort of landscape context I like to see.

One catch. The map viewer has no place-name or site-name search box that I could find. You either pan and zoom, or open the attribute table and filter it. If you know where you're going that's fine. A casual visitor typing "Pentre Ifan" will expect more.

Open data: better than it looks

This is where the geek in me cheered. The data layers sit on public ArcGIS Feature Services, so anyone with a GIS, a QGIS install or a few lines of code can query them directly. The site also says the open datasets from RCAHMW and Cadw can be downloaded from the platform. The NMRW layer carries a clear "Crown copyright: RCAHMW" credit, and the splash screen notes that copyright stays with each contributing body, whose terms apply. Records come in both Welsh and English. Cadw names have a Welsh form ("Beddrod Siambr Bryn Celli Ddu"), and the NMRW has Welsh fields too. There's also a Cymraeg button on the map and a separate Welsh-language hub.

No LiDAR here, though

As a LiDAR obsessive (I built LiDAR Lens for Wiltshire), I looked hard for a hillshade layer and didn't find one in this beta. Wales has good open LiDAR, and a hillshade under the HER points, with a swipe against the enclosure maps, would be a wonderful combination.

On the phone

It works on a phone. The tools sit along the top and the layer list slides up from the bottom. It's a bit cramped, though, and on a narrow screen the Cymraeg button sits over the toolbar. You also have to tick a terms box on every visit before the map will let you in. Both are fair beta niggles.

Verdict

It's an excellent idea: three national datasets, a quarter of a million HER points and a growing library of georeferenced historic maps, all in one free viewer with open services underneath. Add a search box and some LiDAR, and England would have a real reason to be jealous. The beta runs until 1 December 2026 and the team really does want comments, so if you have a Welsh corner you love, give it a try and use the Feedback button on the home page.

The Wiltshire Tornado of 1859: Thirteen Miles of Ruin

At about half-past one on Friday 30 December 1859 a tornado crossed north Wiltshire from Bowood Park, near Calne, to Ogbourne St George. This page is the companion to the short film Thirteen miles of ruin, with the sources behind each card.

The survey

Alfred Charles Smith, rector of Yatesbury, walked the whole track and published his account in the Wiltshire Archaeological and Natural History Magazine the following year. His figures: the storm "shaped its course for E.N.E., and took nearly a straight line in that direction for about thirteen miles, its breadth varying from 250 to about 400 yards". It took two or three minutes to pass any one place. He declined to estimate its forward speed, and no one was killed.

Smith also gave the geometry of the track: "a line drawn from the point of its commencement, one mile south of Calne, to that of its final disappearance at Ogbourn St. George, will very nearly pass through every farm estate and village enumerated above". That line is 12.8 miles long at a true bearing of 76°. The film draws exactly that line, with the places he names plotted beside it at their modern village centres. The red band is a diagram of a 300-yard breadth, not a surveyed boundary.

Smith's line from Bowood to Ogbourne; the red band is a 300-yard diagram, not a surveyed track. Map data © OpenStreetMap contributors.

Along the track

• Bowood Park: "where it broke off the large branch of an oak tree within the precincts of Bowood Park" — the first damage, about a mile south of Calne.
• Quemerford: "astonishing the inmates by bursting in the door and windows".
• Blackland: "swept down no less than one hundred and forty eight trees, some of great size and beauty".
• Hail Farm (now Hayle Farm): "a vast number of trees (amounting in all to about one hundred) were prostrated in every direction".
• Cherhill: "scarcely a tree stands unscathed … and scarcely a cottage retains its roof".
• Yatesbury, Smith's own parish: "taking up a heavy broad-wheeled waggon weighing 22 cwt., and lifting it over a high hedge". 22 cwt is about 1.1 tons.
• Winterbourne Monkton: "the old Rectory House, which had stood for many generations was altogether dismantled and became a ruin".
• Hackpen Hill: "even to the summit of old Hackpen … merely giving a passing salute by scattering a little thatch here and there".
• Temple Farm: "where it overturned several trees, and tore off the thatch of barns and other buildings".
• Ogbourne St George: "where it left its last parting token, by blowing down a small barn and two trees".

Why a tornado

Most trees fell eastward, along the track. The telling exceptions are the trees that fell towards each other: in a triangular meadow west of Cherhill, the trees on both long sides fell inward, and west of Yatesbury churchyard two parallel rows fell across the track towards each other. A few trees fell with their heads to the west, against the gale: two at Quemerford, one at Cherhill, one at Yatesbury. Eastern roof slopes were stripped while the western faces, which took the wind, stayed on. Convergent falls, backward falls and lee-side unroofing are what a rotating vortex explains. George Rowell, who spent three days on the track, could not see a whirl and preferred a downrush of air behind falling rain; four backward trees are a thin sample.

Rowell's sketch map of Cherhill; the arrows show "the direction of the wind, as indicated by the fallen trees".

Hail

At Bowood, Mr Spenser saw hailstones "nearly half an inch in thickness, and from two to three inches in diameter, star-shaped, with rays ranging from four to seven in number". Others were wedge-shaped, about three inches long, and fell clear of the rain.

Rowell's plate of the hailstones.

The weather that day

The NOAA/CIRES/DOE 20th Century Reanalysis (version 3) rebuilds weather maps for 1859 from surface pressure observations. At noon on the 30th the low had moved away to the north and southern England lay in a strong south-westerly. The tornado cannot appear in it: the nearest grid point to Yatesbury is 49 km (30 miles) away, and the track was a few hundred yards wide.

At the Radcliffe Observatory, Oxford, the register for the 30th reads "Stormy", wind south-west, rain 0.37 inch, anemometer 569 miles in the day, about 24 mph. The barometer was rising: 29.133 inches on the 29th, 29.422 on the 30th. The register does not mention the tornado. (Rowell's lecture gives 25½ mph from the west-south-west.)

How strong?

TORRO's list rates the event T6, Calne to Ogbourne St George, ST9769 to SU2074 (Brown, Meaden & Rowe 2013). Read against the TORRO scale, Smith's descriptions — mature elms uprooted, roofs removed in one piece, a garden wall laid flat, a loaded waggon lifted — fall in the T4 range, perhaps T5 if the Winterbourne Monkton rectory walls failed rather than only its roof. That is a reading of the descriptions, not a damage survey.

Notes on the film

• The track is Smith's stated line, not a route joined through village centres. Village points are modern centroids.
• No forward speed is given, because Smith gave none.
• Weather map: 20CRv3 ensemble mean, sea-level pressure every 4 mb, 10 m wind.
• Music: original.

Sources

• Smith, A. C. 1860. The Great Wiltshire Storm of December 30th, 1859. Wiltshire Archaeological and Natural History Magazine 6: 365–388.
• Rowell, G. A. 1860. A Lecture on the Storm in Wiltshire. Oxford.
• Burt, S. (ed.). Radcliffe Observatory, Oxford: meteorological observations 1853–1860. figshare, doi:10.6084/m9.figshare.13333925.
• Slivinski, L. C. et al. 2019. Towards a more reliable historical reanalysis: improvements for version 3 of the Twentieth Century Reanalysis system. Quarterly Journal of the Royal Meteorological Society 145: 2876–2908.
• Brown, P. R., Meaden, G. T. & Rowe, M. W. 2013. Tornadoes in Great Britain and Ireland to 1960: Part 3: years AD 1851–1875. International Journal of Meteorology 38 (378): 68–73.
• Map data © OpenStreetMap contributors.

A Mystery Square in the Stonehenge Landscape

 

Lidar Lens view

About 650 m north-north-east of Stonehenge, just north of the Avenue, there is a square. On the modern Environment Agency lidar it is very obvious: a ditched enclosure about 60 m across, centred at SU 1254 4278, with its sides running close to the grid. So what is it? I don't know, and that's rather the point of this post. It's a little mystery.

Who saw it first?

The first sign I know of was in 2010, when Simon Banton posted a relit image of the early lidar on his blog with a box over this spot marked "What's this then?" That post is no longer online, and I'm grateful to Simon for kindly supplying me with a copy.

Simon Banton's 2010 relit image of the early lidar, "What's this then?" Image: Simon Banton, used with thanks.

Part of something bigger

The Wiltshire & Swindon HER has a record here (MWI79347), from Michael Parker in 2024, for a feature seen on lidar: a circle about 140 m across with "an outer bank and inner ditch plus a raised area internally". I first thought that was something different, as it is round and much bigger. Having measured the lidar properly, I was wrong. The square sits in the middle of a shallow dish about 140–150 m across and 35–45 cm deep, with a low rise round its edge, clearest on the north, south and east. The hollows along the square's north and south sides are the deepest part of the dish, roughly 7–10 cm below the middle of the square and the ground just outside it. So Parker's circle and my square look like parts of the same feature, the circle seen at a broad scale and the square at a fine one.

What it isn't

I can't see it for certain on any of the early aerial photographs. That's perhaps not surprising, as it had been a cultivated, ploughed field.

Nor is it the wartime pillbox that shows on the 1943 USAAF aerial photographs (Currently offline). That stood about 230 m to the west-north-west, at SU 12320 42854.

And it doesn't show on the geophysics. The 2011 magnetometer survey covers the square fully, and there is nothing there (Darvill et al. 2013, Fig. 4B).

A 3D model, and 2001 against 2021

I've put the lidar into an interactive 3D model so you can look for yourself. You can exaggerate the height, move the sun, switch between hillshade, local relief and other views, and draw your own cross-sections. It holds two Environment Agency surveys at 1 m resolution, flown on 8 December 2001 and 4 April 2021. The square and the dish are in both, the same shape to within about a centimetre. Subtract one survey from the other and nothing has changed inside the square beyond the noise: less than 1 cm, when random patches of the same size across the field vary by about 1.5–2 cm. Whatever made it, it was there by 2001 and hasn't changed since.

So what is it?

It isn't a new discovery: Simon Banton spotted it in 2010, and Michael Parker recorded the circle in 2024. It's easy to miss because it is so shallow; it only stands out once the lidar is processed to pick out small changes in height. My first guess was something agricultural, a sheep pen or fold. Having measured it, I'm less sure. Sheepfolds on the chalk usually have a bank, often 0.4 m or more high, with a ditch outside it. This has no bank at the square, just shallow hollows inside a broad dish. Wartime or other military use, a natural hollow in the chalk, or something older all remain possible. If you know better, I'd love to hear.

Acknowledgements

Acknowledgements

Thanks to Simon Banton for a copy of his 2010 blog post.

References

• Banton, S. 2010. 'I love LIDAR and PTM', Novacaster Community blog, 4 Oct 2010 (no longer online; copy kindly supplied by Simon Banton).
• Darvill, T., Lüth, F., Rassmann, K., Fischer, A. & Winkelmann, K. 2013. Stonehenge, Wiltshire, UK: high resolution geophysical surveys in the surrounding landscape, 2011. European Journal of Archaeology 16(1), 63–93. doi:10.1179/1461957112Y.0000000025
• US 7th Photographic Group, 24 Dec 1943, sortie LOC122 frames 1022 and 1050 
• Wiltshire & Swindon HER, MWI79347.
• Environment Agency LIDAR, Open Government Licence.

Stonehenge Aerodrome in 1919: a 3D model from the US National Archives photographs

 Between 1917 and 1921 Stonehenge had an aerodrome for a neighbour, just to the west of the stones on either side of what is now the A303. Almost nothing of it survives on the ground, so I have built a 3D model of its buildings as they stood in early 1919. You can walk round it in your browser here:

Stonehenge Aerodrome, 1919: 3D model

The photographs

The starting point was a set of photographs taken on 20 February 1919 by Lt Sintzenich of the US Army Signal Corps, now held by the US National Archives (NARA). Each one is linked from the model, and here they are:

• 111-SC-153264: “View, looking east, showing a block of six hangars”, taken from the landing ground, with a biplane in an open shed.
• 111-SC-153265: “General view of landing field, with the Night Bombing School in the background”.
• 111-SC-153266: “View of hangars looking west”.
• 111-SC-153267, 111-SC-153268 and 111-SC-153269: three frames of the “Panorama of Stonehenge Camp, looking from southeast to southwest”.
• 111-SC-153276: a vertical view catalogued as the Night Bombing School. That was the other camp, by Fargo Wood, so its buildings are not laid out in this model.

How it was put together

Photographs alone don't tell you where things were, so the layout comes from maps. I traced 41 buildings from the Ordnance Survey six-inch map, Wiltshire LIV.SW, revised 1923, from the National Library of Scotland, and georeferenced it to the National Grid. Anything put up and taken down before 1923 may well be missing.

The big General Service sheds (the hangars) were set out from the RAF vertical photograph of 24 May 1921, reproduced in Martyn Barber's report Stonehenge Aerodrome and the Stonehenge Landscape (Historic England, 2014). It shows three coupled pairs of sheds end to end, with their ridges running north-east to south-west and the doors on the south-west gable ends. The north-easternmost pair, which I've called D, had gone by 1923, so it isn't on the OS map.

For the photographs, I worked back from the bearings of landmarks in each picture (hangar gables, a mast, huts, distant woods) to find where the camera must have stood. Several were taken from the roof of hangar pair B: the field views from its west corner and the camp panorama from its south corner. Photograph 264 was taken from the ground, out on the landing ground south-west of the row.

Using the model

• Photo pegs: the yellow pegs mark where each photograph was taken. Click one (or the numbered buttons) to see the photograph and stand where the photographer stood.
• Click a building to see its name and where the evidence for it comes from.
• Compass: bottom right, so you don't lose your bearings.
• Plan view with the 1923 map: open the plan with the OS overlay to check the model against the map.
• Shed doors: this view looks into the open shed of pair A, where a little biplane sits, as in photograph 264.

Drag to look around, use the wheel to zoom and right-drag to move.

Credits and corrections

Photographs: Lt Sintzenich, US Army Signal Corps, 1919, US National Archives, public domain. Map: OS six-inch Wiltshire LIV.SW (revised 1923), reproduced with the permission of the National Library of Scotland, CC-BY. Hangar layout from Martyn Barber's 2014 Historic England report. Model by Tim Daw.

This is my best reading of the evidence, and I'm sure there are mistakes. If you know the site, the photographs or the aerodrome's history, and something looks wrong, please tell me in the comments. I'll happily fix it.