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.