A burnt mound is an archaeological feature consisting of a mound of shattered stones and charcoal, normally with an adjacent hearth and trough. The trough could be rock-cut, wood-lined or clay-lined to ensure it was watertight. Radiocarbon dates vary quite widely, the earliest being late Neolithic, with clusters of dates between 1900–1500 BC and 1200–800 BC, with some outliers in the Iron Age. There are also some dates that go into the early Medieval period. The technology used at burnt mounds has much greater antiquity and is found from the palaeolithic onwards.
The shattered rock fragments are thought to be the remains of stones heated in fires, which were used to heat water for cooking, bathing, dyeing or leather treatment. The shattering of the rock appears to have been the result of thermal shock when the heated stones were dropped into liquid, normally believed to be water. The mound is assumed to result from the periodic clearing out of the trough, with the stone fragments and charcoal being cast up into a mound. The mound is frequently a crescent shape, which is seen as being the result of the upcast.
The vast majority of burnt mounds are found in the uplands of Britain, and in Ireland where they are called fulachtaí fia. Recognised from the nineteenth century onwards, they attracted little significant interest until the 1980s. In Ireland they are often found in low-lying ground close to water. In Britain, they appeared to have a distribution pattern confined to the higher ground. However, this may be illusory, as examples have been found at lower altitudes during linear route excavations. The reason that they had not been recognised before was that the mounds have been ploughed out, although the trough may partially survive and there will be layers of the burnt mound material surviving as a spread of material. The mixture of burnt and shattered rock with charcoal, labelled as burnt mound material, is found on occasion without the trough. There are settlement sites on Orkney, where the burnt mound material is found as thick layers , but there is no trough to explain the shattering of the rocks.
The upland bias in distribution in Britain has led to a suggestion that they were cooking sites for hunting parties, and there are images from Medieval Irish texts that appear to show this. There are also descriptions of the use of such features for cooking in some of the early Medieval tales, although the historicity of these accounts is open to question. The burnt mounds are always adjacent to water courses, and there can be several instances along the same burn or stream.
There has been considerable debate about the time required to create the mounds. Some interpretations posit the rapid accumulation of material, as a trough was used intensively and very frequently; others suggest a slower accumulation, where the trough was used occasionally over a long period of time. The hunting site explanation would most likely result in the latter pattern of accumulation, while the former would suggest that the use of the trough was for an essentially domestic purpose.
The main explanation for burnt mounds is that they were cooking sites. However, there are problems with such explanations, not the least of which is the lack of any direct evidence of cooking. The process undoubtedly works; experiments were carried out in Ireland in the 1950s to show that a joint of meat could be fully cooked in about three to four hours through this method. However, bone is rarely if ever reported from burnt mound sites, which would be unusual for a cooking site. This has been explained as the result of the soils being too acidic for the bone to be preserved, but this is unsatisfactory. It would be rather unlikely that all of the soils relating to burnt mounds were so acidic that no bone survived, particularly as the pH of the soil will vary considerably from site to site. However, there are examples of burnt mounds that have been recorded on neutral or basic soils, without bone being apparent in the burnt mound material, Alternatives that have been suggested include saunas (where the intention is to create steam rather than cook anything), fulling, salt production, leather preparation etc.
The implication found in many accounts of burnt mounds gives the impression that they are found in Ireland and Scotland, but they also are found in Wales and in England. The Welsh examples tend to be upland and rural, as are many of the English ones, but there are also many found in the lowlying English Midlands. Barfield & Hodder's interpretation of burnt mounds as potentially saunas arose from their various excavations of burnt mounds in the Birmingham area, while more recently forty mounds have been discovered in Birmingham. One example is in Moseley Bog where experiments were made in the late 1990s to assess the plausibility of the sauna hypothesis.
Burnt mounds outside Britain and Ireland
Burnt mound material is also found outside Britain and Ireland, and examples have been found elsewhere in northwestern Europe, such as in Sweden  and Switzerland. It is not necessarily the case that the burnt mound material must have been created for the same purposes, and it would be a mistake to seek a single explanation for all the examples of burnt mounds and burnt mound material. Similar material has been produced all over the world , and there may be a range of explanations.
- Ó Néill, John (2009). "Burnt Mounds in Northern and Western Europe". ISBN 978-3-639-20609-8.
- Barfield, L H; Hodder, M A (1987). Burnt mounds as saunas, and the prehistory of bathing. Antiquity. 61. pp. 370–379.
- O Drisceoil, Diarmuid A (1990). "Fulachta fiadh: the value of early Irish literature". Burnt Offerings (ed) Victor Buckley: 157–164. ISBN 1-869857-07-0.
- Banks, Iain; Dickson, Camilla; Downes, Jane; Robins, Paul; Sanderson, David (1998-9). "Investigating burnt mounds in Clydesdale & Annandale during motorway construction". Glasgow Archaeological Journal. 21 (21): 1–28. doi:10.3366/gas.19126.96.36.199. Check date values in:
- Barber, John (1990). "Burnt mound material on settlement sites in Scotland". Burnt Offerings (ed) Victor Buckley: 92–97. ISBN 1-869857-07-0.
- O'Kelly, Michael J (1954). "Excavations and experiments in ancient Irish cooking-places". Trans Royal Ir Acad. 18: 105–155.
- Barfield, L H (1991). "Hot stones: hot food or hot baths?". Burnt Mounds & Hot Stone Technology (ed) Hodder, M A & Barfield, L H: 59–67.
- "Welsh Contributions". Burnt Offerings: 117–140. 1990. ISBN 1-869857-07-0.
- *Birmingham City Council leaflet by planning archaeologist Archived March 6, 2007, at the Wayback Machine.
- Larsson, Thomas B (1990). "Skärvstenhögar - the burnt mounds of Sweden". Burnt Offerings (ed) Victor Buckley: 142–153. ISBN 1-869857-07-0.
- Ramseyer, D (1991). "Bronze and Iron Age cooking ovens in Switzerland". Burnt Mounds & Hot Stone Technology: 71–91.
- Campling, N R (1991). "An earth oven from British Columbia, Canada". Burnt Mounds & Hot Stone Technology: 93–95.
- Hurl, Declan (1990). "An anthropologist's tale". Burnt Offerings (ed) Victor Buckley: 154–156. ISBN 1-869857-07-0.
- Academic books
- Academic articles
- Barfield, Lawrence & Hodder, Mike (1987). "Burnt mounds as saunas, and the prehistory of bathing". Antiquity. The Antiquity Trust. 61: 370–379.
- Chapple, Robert M. (2007). "The excavation of a burnt mound at Ballywilliam, County Down". Ulster Journal of Archaeology. 66: 21–38.