Hoppenwood Bank: exploring a burnt-mound landscape

Burnt mounds are an archaeological enigma: recent discoveries at Hoppenwood Bank, a bog near Bamburgh in Northumberland, call into question even the little we thought we knew. They show that some of these mainly Bronze Age features date back to the Early Neolithic, and are associated here with a series of substantial timber platforms. Graeme Young, of the Bamburgh Research Project, explains.

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The term โ€˜burnt moundโ€™ is applied to a type of prehistoric monument seen all over the British Isles and parts of Western Europe. These are mounds of fire-affected stones, often fractured by being exposed repeatedly to fire. It is not uncommon to find large quantities of charcoal mixed in with the stones, and it is assumed that they are formed by the discarding of stone and fire-waste from some sort of process that has been undertaken, repeatedly, in the vicinity.

Radiocarbon dating tells us that the majority were created in the Early Bronze Age (roughly 2300 to 2000 BC). Many mounds of this period are found adjacent to, or overlying, a timber- or stone-lined trough. It is assumed that this held water, which was heated to boiling point by adding the heated stones.

Why was hot water needed in such quantities? Archaeologists often disagree over how to interpret features. In the case of burnt mounds, there are very many competing ideas. It has been suggested that the heated stones were used to provide steam for a sweat lodge, like a sauna. Brewing has also been very plausibly proposed (CA 256), as have industrial processes connected to tanning and metal-working. Or perhaps the water was just used to cook food in large quantities for feasting.

This site-plan shows the areas that have been investigated by the Bamburgh Research Project team.

Our recent work at Hoppenwood Bank has, if anything, deepened the mystery of these unusual mounds, extending the date range and showing that while most mounds are found next to streams, they also occur beside the relatively still waters of a lake and, as the evidence here increasingly seems to suggest, on the edge of a reed bog.

The Bradford Kaims Wetland Heritage Project

Our discoveries were made as part of the Bradford Kaims Wetland Heritage Project, which is being undertaken as part of the wider Bamburgh Research Project. It represents a first phase of investigation in what we hope will be a long-term, community-supported study of a fascinating landscape, made up of a series of former lakes, in-filled with peat over the 15,000 years or so since the end of the last Ice Age. We aim to identify archaeological sites, map the extent of the wetland within our sample area using coring and topographical survey, and investigate areas of particular interest with trial-trenching.

Cleaning Burnt Mound 1 earlier this year. The depth of the mound is visible in the section, while, in the background, tarpaulins are being removed from a Neolithic wooden platform found on the site.

For our pilot study area, we chose the landscape to the immediate south of Hoppen Hall Farm, lying on the northern and eastern part of one of the larger former lakes. South of the study area, parts of this still survive as open wetland, now designated as Embletonโ€™s Bog, a Site of Special Scientific Interest. We started by mapping the lake though aerial photography, determining that it originally extended for 950m north to south, and 1,000m east to west, draining through a small channel at its northern end, past the base of Hoppenwood Bank, before opening out into a further smaller lake to the north, and ultimately draining into Budle Bay, an inlet of the North Sea, 5km to the north.

This deep core shows silt sediment and light covered marl towards the base of the section. Peat formation is visible towards the top. It is increasingly clear that the infilling of the lake with peat occurred at an early date, so that the lake had already become a bog by the Neolithic.

Survey and test-pitting

A test-pitting survey was undertaken initially to investigate the margins of the former lake by identifying the extent of the peat in relation to the areaโ€™s surface topography. The survey also served as a random archaeological sample of the area, intended to identify features of archaeological interest. This was how we came across our first burnt mound (Mound 1) during the initial phase of random sampling. In two of our test-pits, at the base of Hoppenwood Bank, we encountered an unusual burnt deposit of dolerite, sandstone, and ironstone in a silt matrix with a high charcoal content. We decided to extend the excavation area to investigate further, and this revealed a highly unusual hearth-like stone feature, formed from 15 fire-affected sandstone slabs, measuring around 1.2m north-west to south-east by 1.1m south-west to north-east.

The hearth gives us our best dating evidence. Archaeomagnetic analysis undertaken by Sam Harris of Bradford University gave us a date for the last firing of the hearth at 4230 BC (ยฑ235 years at 95% confidence). That is very early: it dates back to the very beginning of the Neolithic in the region, and must surely be among the oldest known, though it is not alone and has proved to be just one component in a complex landscape.

Burnt Mound 2, found in 2012, lies in the foreground, while the first burnt mound is off centre to the right, at the top of the image near the bell tent. The extent of the flooding in that year is apparent, and clearly outlines the spur of higher ground extending into the bog area. This aerial photograph of the site was taken by Horizon AP using a four-rotor drone.

We also investigated the deeper parts of the peat basins, using a series of core transects intended to map the profile of the wetland in the vicinity. This identified a ridge of dryer ground, which we thought might be suitable for a magnetometry survey. Based on some 10m ร— 20m square grids, covering an area 40m by 95m, the survey revealed a series of anomalies, suggesting a substantial background of activity on the ridge.

The largest of these was a broadly circular, high-response feature measuring some 14m across. This appeared sufficiently strong to indicate burned or fire-affected material as a component of the feature. From later trenching work, we identified this as our second burnt mound, lying some 140m to the south-west of Mound 1.

When the second mound was investigated, it too was found to be made up of imported dolerite, sandstone, and ironstone fragments, many of which showed signs of having been fire-affected. In the centre of the mound, we found a sandstone slab set on edge. This formed the head of a trough, now filled by a succession of silt-rich soils containing a high proportion of charcoal, a feature commonly associated with burnt mounds of Early Bronze Age date; such a date for this mound was supported by the few finds recovered from the moundโ€™s surface.

The continuation of the test-pitting programme has revealed that the two mounds are not alone. Areas of higher ground that were identified as supporting different vegetation, such as increased concentrations of nettles, were targeted during 2013. This turned out to be a fruitful endeavour, and a number of additional concentrations of burnt stone and charcoal were identified, indicating the presence of further burnt mounds following the contour of the higher ground, just above the wetland basin. Numbers remain problematic, and will probably rise, but at present
we appear to have at least 12 burnt mounds.

This sondage through the unburnt mound shows that it was constructed of stones supported by a timber/brushwood platform lying over the peat layers โ€“ an enigmatic feature that we hope to investigate further in the future.

More mounds: this time of unburnt stone

The dry summer of 2013 substantially lowered the water table compared to that of the previous two seasons, allowing a more extensive investigation into the peat basin, an area that was completely dry in June and July 2013, even though it had been inundated with flood water only months earlier โ€“ clear demonstration that the landscape remains dynamic.

This investigation revealed a further series of stone mounds, but these were unburned and located within the former wetland, not on the adjacent dry land. They seemed to form a distinct line, and when one of the mounds was sampled it proved to be composed of small to large irregularly shaped sandstone fragments, stacked 0.6m thick on top of a roundwood timber raft, laid directly on to the peat.

Some small test-pits sunk between two of these low-lying mounds suggests that they were connected by a brushwood track. The extent of the mound alignment has yet to be identified, but certainly extends for some tens of metres, and comprises at least a further three mounds. As of yet, we have no archaeological dating evidence for these strange features.

Timber platform

The low water table also allowed us to undertake further work on Mound 1, which turned out to be far more complex than originally thought. Instead of comprising a single large mound, we now know that it consists of at least five smaller, though still substantial, mounds, each some 5m across and around 0.5m or more thick, spread across an area of at least 13m.

Another surprise awaited when we extended the excavation trench south-westwards into the wetland area. Here we found a large timber platform formed from roundwood branches pegged into the upper peat layers. A similar platform, found at Eskmeals in Cumbria, and dated to the Mesolithic, has been proposed as an attempt at ground stabilisation; this could be the same at our site, the structure providing dry access to open water within the lake system. Whatever its function, it is clear that the platform is substantial, as it continues along the base of the burnt mound for more than 9m, and it extends for at least 11m.

This test-pit over the area of the timber platform was intended to investigate its form, and to demonstrate how consistent and extensive it is in the immediate area of the burnt mound.

By the end of 2013, we still had not excavated the full extent of this feature, but it was clear that it overlay the most extensive of the burnt mounds, and that it was covered by at least one later period of mound deposition, suggesting strongly that it was contemporary with the period of mound formation.

The plot thickened further during our 2014 season of work, when coring undertaken by Dr Richard Tipping of Stirling University in the area of the platform indicated the potential presence of a series of earlier platforms, underlying the top one to a depth of 1.2m and including some huge timber posts. An immediate question in our minds was whether the numerous burnt-mound phases could be matched by a similar number of platforms.

Excavating the upper part of the platform with a bamboo tool. A Neolithic wooden paddle was found lying on top of it.

Pottery and a paddle

The later overlying phase of mound accumulation produced a number of fragments of pottery provisionally identified as Carinated Bowl, the earliest type of pottery found in Britain and Ireland, typical of the earliest Neolithic phase (c.4000 BC) and consistent with that Early Neolithic date obtained for the hearth, though the pottery could be Bronze Age; we will not know for sure until the carbon dates have been obtained. It certainly looks at the moment as if the platforms and mounds are contemporary, and are part of the same complex of activity.

In 2013, the roundwood platform produced the very exciting find of a timber paddle, preserved by the peat layers on the surface of the platform. The paddleโ€™s preservation was doubly fortunate: a modern field drain had just missed slicing through it, and had it lain only centimetres higher it would have been above the anaerobic horizon and would have decomposed long ago. The paddle was mostly intact, though the tip of its handle may have been detached and laid next to it. The asymmetrical shape, with the handle being an extension of one side of the blade, is unusual for a boat or canoe paddle; instead, it might have been one of a pair of paddles used for picking up the heated stones of the mound.

Starting the half section of the timber โ€˜troughโ€™. The southern side has been slightly truncated by the double drain that just missed the paddle found in 2013. Photographed after half sectioning was complete, the trough shows the surprisingly clean water that accumulates in it. No attempt will be made to lift this feature this year, as it is too substantial, so its recovery will need a great deal of planning.

In 2014, we found a further peat-preserved timber feature in the form of a hollowed-out tree trunk set vertically into the ground โ€“ this time beneath a phase of burnt mound, but dug into the underlying waterlogged layers, thus ensuring its preservation. This may well represent a timber trough, where the hot stones of the mound were plunged into water to heat it, but other interpretations are possible.

For example, when we half sectioned the fill it became apparent that there was a clay base present, and that clean-looking water had accumulated within it. This raised the possibility that the feature itself could have been used like the lining of a well, as a source of water. Coring work increasingly suggests that the lake itself filled in and was transformed into a bog quite early on, which would make fetching clean water from the remaining open lake areas increasingly problematic. Of course, it is quite possible that a former trough could have been put to this secondary use at the end of its life.

What could it mean?

It is early days in our investigation of this complex landscape, and we are facing a series of questions. First, though the two mounds are similar in scale, and both were formed as a result of large-scale discarding of stones that had been heated in a fire, they are clearly different, not least in their widely separated dates.

The second mound can be provisionally dated to the Bronze Age by its finds assemblage, and this accords with the expected date range for such mounds, as does the presence of the stone-lined trough. By contrast, the very early Neolithic date of Mound 1 places it in the realm of the unexpected. It is not alone, however: recent work in Ireland has identified Early Neolithic examples at Ferriterโ€™s Cove, County Kerry, and at Fanore More, County Clare.

The presence of a clearly defined stone hearth in Mound 1 was unusual, though again not without parallel: a similar stone setting was noted at the Mound 1 site at Titlington, some 19km to the south-west, excavated by Pete Topping in 1998. What really sets Mound 1 apart, however, is the series of timber platforms that now look, almost certainly, to be associated with the accumulation of the burnt mound. If the two features were functionally related, then we have to ask what the platforms were used for. Could they have provided access to open water, or served as landing platforms for those whose activity formed the burnt mounds?

Excavating a test-pit over the Neolithic wooden platform. The buckets contain environmental samples.
Hoppenwood Bank has produced a number of thought-provoking finds. Bamburgh Research Project Director Paul Gething (on the left) and Supervisor Tom Gardner (right) ponder the next phase of research.

One thing is clear, the interpretation of the mounds and understanding the processes that led to their formation, as Tom Gardner the Trench Supervisor has said from the start, will depend on looking for, and understanding, the features beyond the mound itself. Here we can hope to find evidence of the processes that required all the hot stones, not just the discarded stones themselves which merely represent the waste product.

How much continuity?

The 2,000-year gap between the two mound areas certainly provokes some interesting thoughts regarding how long the process that required so many hot stones was going on at the site. Are we dealing with two distinct periods of activity, and two distinct processes that just happen to utilise heated stone? And is Mound 1โ€™s timber platform significant in this regard? The evidence so far is too limited to draw firm conclusions, but the sheer number of mounds in the near vicinity of the wetland clearly hints at long-term use and a degree of continuity.

If so, was there something about this site that had particular significance to the people who came here on a regular basis for some kind of communal activity during the prehistoric period. A great deal more work is needed to place the current discoveries into a better context, and to understand more fully how the wetland developed and was exploited by the prehistoric population.

In this context, the second series of unburned mounds, so far undated, which appear to form a line of small artificial islets connected by a trackway extending into the wetland, is very intriguing. It seems logical to assume that they were constructed at a time when the area consisted of bog and open water. This in itself indicates a relatively early date, because pollen and sediment data suggests that water levels were falling and the bog was becoming increasingly dry by the Early Neolithic. It is conceivable that they represent no more than a dry route across the bog related to transport, wild-fowling or fishing, but a more ritualistic function is always possible โ€“ or indeed both.

Experimental archaeology: one theory is that burnt mounds are the result of large-scale brewing. The team decided to put this to the test using a trough donated by the farmer. The photographs show barley and honey being added to the stone-heated water by Project Director Paul Gething.

Direct dating and a better understanding of the extent and form of these features will certainly be a priority for the future, so long as the weather is kind! In the meantime, we need to keep an open mind, and perhaps not look at these heaps of burnt stones as representing the result of a single process โ€“ brewing, cooking or sauna โ€“ but rather see them as being formed over a very long period of time, and possibly for a number of different practical and ritual processes.

Experimental archaeology continued: the hydrometer shows that the brew is getting along nicely. In their eagerness to sample the resulting beer, nobody remembered to take pictures of the final product. It was described as โ€˜interesting โ€“ drinkable โ€“ but not something you would want to consume every dayโ€™.

Acknowledgements

The authors are particularly grateful to the Northumberland Estate and the tenant farmers, Mr Brown and Miss Barber, for the opportunity to work in this extraordinary landscape and for their support. The project was jointly funded by the Heritage Lottery Fund, English Heritage, and the Bamburgh Research Project. Many volunteers and students contributed hugely to the success of the project, and we would like to take this opportunity to thank them for their efforts and enthusiasm, and hope that many will be able to continue to work with us in the future.

All IMAGES: Bamburgh Research Project.