Re-excavating Arminghall Henge: a burnt timber circle from prehistoric Norfolk | The Past

Last September, an excavation at Arminghall Henge in Norfolk reopened a trench first dug by Grahame Clark almost a century earlier – revealing a glimpse of a large timber monument that may have met a fiery end. Andy Hutcheson, Matt Brudenell, and Mark Knight report.

On a clear day in June 1929, Wing Commander Gilbert Insall was flying over Caistor St Edmund Roman town in Norfolk (Venta Icenorum; see CA 270) when he spotted cropmarks near the confluence of the rivers Tas and Yare. Archaeological interest in Caistor and its environs was already intense thanks to the remarkable photographs of cropmarks that had been taken within the town’s walls during the dry summer of 1928 (reported on by Mortimer Wheeler in the June 1929 edition of Antiquity), but these new markings would prove to be much older. SWE Excavator Oil Seal

Re-excavating Arminghall Henge: a burnt timber circle from prehistoric Norfolk | The Past

Insall was a hero of the First World War, having been awarded the Victoria Cross for conspicuous bravery, skill, and determination as an aviator in 1915, and in peacetime he became an expert in the fast-developing field of aerial archaeological reconnaissance. In 1925, he had discovered the Neolithic timber monument known as Woodhenge, leading to Maud Cunnington’s excavations of 1926-1928, and Insall recognised the similarities of the cropmarks he had spotted flying over Caistor to those in Wiltshire. He was not alone in this observation: in the September 1929 edition of Antiquity, O G S Crawford reported that ‘another Woodhenge has been found, just outside the city of Norwich’.

Soon after the site’s discovery, it attracted the attention of Grahame Clark, who was working at Cambridge University’s Department of Archaeology and Ethnography, and would become renowned for his work at Star Carr 20 years later. Clark noted that the position of the monument – known as Arminghall Henge – on the outskirts of Norwich left it vulnerable to destruction from the city’s growing infrastructural needs. A century earlier, its landscape setting had been significantly impacted by the construction of the railway line linking Norwich to the wider rail network in the 1840s, but most pressing in the early 1930s was the building of electricity pylons, which still mar its setting today.

A large steel pylon had already been constructed within the confines of the henge, close to its southern entrance and between its inner and outer ditches, and it was recognised that the threat was real and immediate – although the monument was scheduled, its setting was likely to be further affected by development. Additional aerial survey and work on the ground had established that there were a significant number of monuments near Arminghall Henge, including many ring-ditches, as well as another intriguing monument to the south-west at Markshall, also discovered by Insall in 1929, which consisted of a double ring next to a D-shaped enclosure. It was clear that archaeologists needed to characterise Arminghall Henge more fully to understand its significance in regional and national terms.

Clark’s window for excavation was brief – five weeks during August and early September 1935 – but productive. At the head of a team of three other archaeologists (Rainbird Clarke, C W Phillips, and Mollie White), and with four unnamed men to carry out the bulk of the labour, he was able to open a trench that investigated the full extent of the central timber circle along with its inner and outer ditches and the inner causeway. His results were remarkable given the limitations of the team’s size, demonstrating that those involved were highly skilled field archaeologists.

Clark’s investigation was able to unpick the monument’s various components, shedding light on the sequence in which it was put together. The post-holes were all large, containing post-pipes suggesting timbers around 1m in diameter, and each post-hole also had an associated linear slot, dug at the time of the monument’s creation to allow the timbers to slide into place. All of these were orientated to the south, except for Post-hole 5, whose slot faced in a more south-easterly direction. Strikingly, the post-holes were all located close to the henge’s inner ditch (and, beyond that, the bank) rather than towards the causeway. This would have made it difficult to bring the large timbers, estimated at weighing perhaps as much as 5 tonnes, into position, and so it therefore seems likely that the timber circle pre-dates the earthworks of the henge, representing its earliest phase.

Clark’s excavation recovered 16 sherds of pottery from a charcoal-dense deposit at the base of the inner ditch, all of which came from a rusticated Beaker pot decorated with thumb-nail impressions. The position of this material at the base of the ditch is important, and may give a reasonable date for the construction of this feature – and therefore its associated bank. Clark believed that this deposit dated to the monument’s earliest phase, and that dating the pottery would provide a good date for its inception. He also believed, based on his assessment of where similar pots had been found, that these sherds were often associated with Beaker pottery and therefore dated to the very beginning of the Bronze Age.

Little changed for Arminghall Henge until November 1960, when Grahame Clark wrote to Rainbird Clarke – who by that time was Curator and Keeper of Archaeology at Norwich Castle Museum – to suggest that the time had come to make a request to the British Museum Laboratory to radiocarbon-date (a technique invented in the late 1940s) charcoal collected from the site’s Post-hole 7. Rainbird Clarke duly submitted a sample, and the following year received a result of 4440±150 BP (c.2500 BC) from Gale Sieveking, then Assistant Keeper of Archaeology at the British Museum.

Subsequent correspondence between Clarke and Sieveking survives, illuminating their thought processes and how understanding of the site developed. They discuss the nature of the charcoal sample and the limitations of dating large mature timbers, and debate what the date represented – Clarke queried whether it showed when the tree was cut, was converted into a post, or its initial growth. He also noted that the sample had come from the centre of the tree, as that was all that was available. Sieveking wrote to the Director of Kew Gardens to seek further advice about the tree’s likely age, and was told that a post of 3ft in diameter might have come from a tree no more than 120 years old. The Director suggested, too, that it would be useful to go back and obtain further samples from undisturbed post-holes – to which Clarke agreed, but he died the following year before this could be done.

Since then, though, a more recent reassessment of the radiocarbon date from Post-hole 7 has given a calibrated date range of 3525-2700 cal BC – rather earlier than was assumed in the 1960s, and essentially taking in most of the Neolithic. That broad range, coupled with the rusticated Beaker from the charcoal-rich layer at the base of the ditch, provides little clear insight into either the date for the construction of timber circle or for the henge itself. We hoped to shed more light on the matter through a new excavation on the site, and that work was undertaken last year.

The 2022 investigation involved a team of people from the Sainsbury Institute for the Study of Japanese Arts and Culture at the University of East Anglia and the Cambridge Archaeological Unit, supporting a group of volunteers, along with members of the Restoration Trust, a charity helping people suffering from low mental-health through creating opportunities to get involved in local heritage projects. We also worked in partnership with the Norfolk and Norwich Archaeological Society, who generously supported the work together with the National Lottery Heritage Fund and the Society of Antiquaries of London. Our excavation was a more modest undertaking than that of 1935: the key aim was to reopen Clark’s trench and recover further materials that we could use to re-examine the monument’s date and try to establish a chronological sequence for its construction. First, though, let’s establish the background that we were working from.

Our work came as part of the Later Prehistoric Norfolk Project (, which aims to improve understanding of the county’s rich archaeological record, and the wealth of information that has arisen from remote-sensing and aerial photography. These methods have provided an increasingly detailed picture of Norfolk’s prehistoric landscapes, greatly aided by the decades-long National Mapping Project (funded by Historic England) and, more recently, the availability of LiDAR. Targeted fieldwork remains rare, however – which is where our work on Arminghall Henge and its immediate landscape came in.

We began by studying existing records for the site which, in addition to Clark’s 1936 excavation report – published in the Proceedings of the Prehistoric Society just a year after the excavation – consisted of aerial photographs of the area and information logged in the Norfolk Historic Environment Record. Using these, we can see a dense grouping of later Neolithic and early Bronze Age monuments to the south of Norwich, where three rivers – the Tas, Yare, and Wensum – meet in proximity. Arminghall Henge lies within this grouping, and it has previously been suggested that it may have represented a focus of, and perhaps an early element within, a ritual landscape.

From these records we also know that a double-ditched barrow located about 150m north-east of the henge was excavated by Rainbird Clarke in the 1950s – it has since been destroyed by the construction of an electricity substation. When this facility was extended in 1968, Keith Wade excavated the remaining elements of the barrow; both sets of work were later published by Frances Healy in the 1980s, and three pits within its circumference were dated.

Pit 1, at the centre of the barrow, produced charcoal from a mature timber that was radiocarbon dated to 2470-2025 cal BC, as well as a grooved sandstone object, six sherds of a European Bell Beaker, and a crushed but complete Developed Southern Beaker. Dark streaks observed in the pit section may represent the remains of an inhumation or a tree trunk coffin. Charcoal from Pit 2, also located near the centre of the barrow, gave a radiocarbon date of 2460-1985 cal BC. Pit 5 lay off-centre within the inner ring-ditch; it yielded oak charcoal that was radiocarbon dated to 2115-1695 cal BC, as well as friable materials that the excavator thought were the remains of a hide or sheepskin.

Further clues came during the construction of the Norwich Southern Bypass in the 1990s. This project rerouted the A47 to the south of Norwich, and also provided an opportunity for the Norfolk Archaeological Unit, led by the late Trevor Ashwin, to carry out an excavation ahead of construction. During this initiative, they explored three ring-ditches on higher ground about 600-700m to the south-west of Arminghall Henge: these were found to contain graves which produced a handful of radiocarbon dates. A cremation located just off-centre within one of the barrows (NHER Site 9585) contained a small Collared Urn and produced an unusually early date of 2860-2495 cal BC, but it was only one of a complex group of intercutting cremations at the barrow’s heart. The earliest date for the most northerly barrow (NHER Site 6099) in this group was again from a cremation, this time containing a copper-alloy pin dated to 2845-2335 cal BC.

What would our work add to this picture? In August 2022, our investigations began with a magnetometry survey of the field in which Arminghall Henge lies. Unsurprisingly, the field – which consists of river-terrace gravels and has been traversed by electricity lines – was magnetically noisy, but we could still pick out a number of features. The geophysics clearly showed up the henge ditches, several of the timber post-holes, and the second circle, along with a set of archaeological features in its immediate vicinity that may be part of a prehistoric or Romano-British field system. The gravel-extraction pit associated with the construction of the railway and latterly used as an informal rubbish dump can be clearly seen on the geophysics, too, lying 50m west of the henge.

Following the geophysical survey, it was time for excavation to begin. The first step was to reopen Clark’s trench and clean the section that he had drawn and published in 1936. Within this, we re-excavated Post-hole 3, and sample-excavated the previously untouched Post-hole 2; both contained charcoal and were sampled. During our fieldwork, we were able to test some of the excavation techniques and assumptions made by our predecessors, and their interpretations were largely proven correct – as an exercise examining the methodological history of the subject, it was valuable to see just how good the 1930s excavators had been, and a tribute Clark’s abilities.

Our work has thrown up some interesting new results, however. As well as reopening Clark’s trench, we opened a transect between the henge and the current course of the River Tas (which was canalised in the 1840s at the time that the railway was constructed). This allowed for geoarchaeological sampling of the field, helping us to put the henge in its prehistoric context. We were able to uncover a sequence of Pleistocene gravels and establish that the old position of the river lies to the west of its current location; no alluvial deposits were encountered to the east of its present route. Arminghall Henge itself lies on the terrace, and once possessed a sharp scarp to the north and west, which would have made the monument’s position, as seen from the river, more impressive than the relatively gentle slope that it now occupies. The scarp had been infilled with hill wash, possibly resulting from ploughing in later prehistory. Meanwhile, a trench dug through the second circle to the north of the henge found a relatively shallow ditch associated with some worked flint. Its shallow depth might suggest that this was originally a pond or disc barrow.

What about the two post-holes? After excavating Post-holes 2 and 3 and comparing them with the 1935 section drawings, we can see that they were remarkably similar. Both had post-pipes containing charcoal in the section, and both faced in the same direction, roughly south, aligned with the post-slot that was originally used to place the timbers in their settings. The process that led to this appearance is open to interpretation. One possibility is that the timbers were burnt in situ in prehistory, and then removed, with the post-slot perhaps providing the least resistance for extraction compared with the surrounding gravels. If true, this would have been a truly remarkable sight with, potentially, all eight of the timbers set alight at once, effectively bringing the timber monument to an end in a powerfully visual event.

Another intriguing possibility presented by the burnt material found during the 1935 excavation and re-exposed in our work is that the charcoal and heat-affected flint went into the base of the ditch hot. Our investigations showed that the gravel under this material was a pale pink-red, discoloured by heat – raising the possibility that some of the debris from the burning of the timber circle had ended up in the freshly excavated ditch, along with the 16 sherds of rusticated Beaker discovered by Clark’s team. Are we therefore seeing the end of one monument – the timber circle – and its replacement with a new monument, the henge? We are now in the process of analysing the samples taken from both the post-holes and the base of the ditch, and we are optimistic about there being highly appropriate material for dating both of these monuments and establishing their respective chronologies. We hope to have a new set of radiocarbon dates to discuss soon.

Above all, both the 1935 work and our more recent investigation have established that the henge remained a place of interest during later periods of the site’s use. We can see this in the continued use of nearby barrows as funerary monuments, and there was also a significant assemblage of Iron Age pottery in the middle fills of the inner and outer ditches, showing continuing use of the monument in later prehistory. The inner ditch attracted attention in the Roman period, too, with the deposition of a significant amount of pottery and metalwork, including coinage. One of the coins, recovered from the ditch’s middle fills, dated to Hadrian’s reign in the early 2nd century, but Roman material continued to be dumped through to the 4th century. This suggests that the monument may still have been viewed as sacred even at that time, and continued to be a focus of religious activity.

Outside the henge, our test-pitting found very little cultural material from prehistory or the Roman period, and little evidence of medieval activity, but there was an uptick in activity in the 16th and 17th century, when the field may have been used for night-soiling. There was also a fair amount of modern material in the topsoil, though the hillwash was generally very clean.

As well as exploring Norfolk’s regional archaeology, the Later Prehistoric Norfolk Project aims to compare the county with archaeological landscapes in Japan, exploring themes that are mirrored across both island nations, such as insularity and periodic evidence for the exchange of ideas with their local continents; it coincides with the Circles of Stone exhibition currently running at the Stonehenge Visitor Centre (see CA 393), which compares monuments built in Britain and Japan.

So, what now? Our immediate next steps involve redating Arminghall Henge and reassessing its surrounding landscape, but this summer our plans will see us move to another iconic monument from Norfolk’s prehistory: Warham Camp ‘Hillfort’. There, too, we hope to re-explore previous excavations, and to add to our understanding of that part of the county’s past.

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