Finding the New Rome
Voting for archaeology
Editor Simon Denison
Living under a medieval field
John Letts reports on the remarkable evidence for medieval cereal crops and weeds that survives in the thatched roofs of southern England
'Fful sooty was hir bour and eke hir halle' (Chaucer, The Nun's Priest's Tale)
In the autumn of 1992 a sample of roofing thatch blackened by smoke was delivered to me at the environmental archaeology lab at Oxford University. No archaeologist had ever looked at this sort of material before, as it had simply not occurred to anybody that ancient thatch might be of interest.
This small shoe-box full of sooty ears of wheat sparked off a continuing research project which is transforming our understanding of medieval agriculture, and opened conservationists' eyes to the widespread survival of ancient thatch on England's vernacular buildings.
The first sample came from a late 15th century building in Buckinghamshire, and a little investigation showed that it was an original piece of thatch that had survived undisturbed for 500 years. I have now gathered samples from some 50 buildings, and in situ examples survive in at least 200 buildings overall in southern England.
At first the survival of any ancient thatch seemed almost miraculous. Not only is thatch organic and prone to decay, but the traditional thatcher's technique of renewing a straw roof every 25-35 years led to the view that all surviving thatched roofs must be of relatively recent date.
Yet although thatched roofs were renewed, the traditional technique was simply to add fresh straw layers without disturbing the underlying base coats. This has led to accumulations of thatch up to 7ft (2m) thick on roofs dating from the 14th-16th centuries, and in many cases the base coats have never been disturbed.
This material has survived primarily because it was kept dry for centuries, but a heavy encrustation of soot from the open fires which smouldered below them also discouraged insect and fungal attack. This smoke-blackening is characteristic of medieval buildings in England, where only high-status homes were constructed with chimneys and fireplaces prior to 'the great rebuilding' of 1550-1650 AD.
Until this time, most of the population lived in dark, smoke-filled cottages heated by open fires kindled in the centre of an 'open hall'. The hall was the centre of domestic life, and the smoke of the open hearth drifted into the roof space unhindered by ceilings, escaping either through a louvre or through doors and windows.
Over several generations, the smoke from heating and cooking-fires deposited soot several centimetres thick on the rafters and base coat of thatch, thereby marking its late medieval origin for botanical sleuths of a later age. In the late 16th and 17th centuries when open halls were divided into two storeys, and enclosed fireplaces became fashionable, 'smoke hoods' and chimney stacks were constructed to contain the smoke of open fires. These were raised up through the thatched roof without disturbing the sooted base coat and the younger layers of thatch above it.
The general architectural dating of smoke-blackened thatch has recently been bolstered by the results of exploratory radiocarbon dating of two samples removed from the base coats of former open hall buildings in Devon. The samples came from discrete contexts uncontaminated by later material. They provided dates of about ad 1450-1525, which accord well with the architectural evidence for the foundation date of the buildings.
The archaeological value of medieval thatch goes well beyond the simple fact of its survival - however extraordinary that may be. These base coats contain the best preserved late medieval cereal remains ever recovered in western Europe, and include complete ears with intact grain and straw, as well as crop weeds and other vegetables.
Hitherto, evidence of the crops grown in medieval times has come from the analysis of charred and waterlogged remains from excavations, occasional herbarium specimens, descriptions in herbals and botanical inference. All of these sources can help improve our understanding of medieval agriculture, but smoke-blackened thatch provides researchers with their first opportunity to hold a largely intact medieval crop in their hands.
The sequences of straw layers, built up over five centuries, record the changes that occurred in cereal crops as a result of plant breeding as well as changes in the ecology of cereal fields.
Working with thatchers and building historians, I have now surveyed and excavated over 200 ancient thatched roofs exposing large quantities of well-preserved medieval and later material. Most samples contain 'land race' mixtures of bread wheat (Triticum aestivum), English rivet wheat (Triticum turgidum) and rye (Secale cereale) which grew to 6ft (1.8m) or more in height - far taller than modern varieties - as well as barley (Hordeam vulgare) and oats (Avena spp).
Land races evolve over many centuries when crops are grown in heterogeneous conditions, year after year, from seed saved from the previous year's crop. The result is that every plant in a land race is slightly different from its neighbour, and medieval cereals were consequently very uneven in straw height, ripening time, grain yield and other agronomic traits. This diversity ensured that a portion of the crop almost always set seed irrespective of the many environmental stresses that can destroy a crop such as drought, waterlogging, frost or crop disease.
This 'biodiversity' had accumulated in English wheat fields since the introduction of farming in the Neolithic period, but was mostly lost over the course of the 19th century as farmers adopted improved cultivars created by scientific plant breeders. The cereals in medieval thatch samples stand in stark contrast to the monocultures of genetically uniform varieties that are grown for flour and thatching straw today.
Bread wheat is the most common cereal present in the medieval thatch, but 60 per cent of the samples contain 'rivet' wheat - a species that has not been grown commercially in Britain since the late 19th century. Many rivet varieties produce excellent thatching straw, however, as late medieval herbals and agricultural treatises confirm.
Many of the samples appear to be composed of threshing waste that was used to form a base coat for external 'spar' coats of higher quality straw. These threshing waste samples are also rich in crop weeds and legumes, many of which are now rare or extinct in Britain. Among the approximately 35 species of weeds identified so far, some such as charlock, mayweed, docks and thistles are still despised by cereal farmers today; others, such as corn cockle and cornflower, have now been extirpated from English fields.
Leguminous plants such as cultivated peas and broad beans are also found. Both were staple crops and probably represent plants carried over from previous rotations. Other weed species found include bracken, which is now associated with acidic grassland rather than arable fields. It probably grew happily in damp furrows and field margins, and was widely used for bedding and fuel.
All the 200 or so known examples of medieval thatch are in southern England, and the vast majority are in Devon. No smoke-blackened thatch survives north of a line from the Wash to the Severn. Most southern counties contain fewer than three or four examples, and several counties have lost their last smoke-blackened thatch within the past five to ten years.
The arrangement and integrity of the rafters, wattles, battens and fixings in most of the buildings with medieval thatch suggest that their base coats were applied when the buildings were first constructed. The architectural evidence suggests that most of the non- Devon buildings date from the late 14th and 15th centuries, while the Devon examples are primarily late 15th century. All these buildings functioned initially as open halls, and the lack of embellishment on their internal timberwork suggests the majority were not of manorial status. Most, it seems, were built by wealthy villeins who had adapted successfully to the economic restructuring of the late medieval period, and later by the yeoman farmers whose investments in housing contributed to the construction boom of the 16th and 17th centuries.
Medieval thatch only survives in roofs where base coats were never stripped and where the weathering surface was replaced on a regular basis. Much ancient thatch probably owes its survival to the use of wooden pegs to fix battens to the rafters rather than iron nails, for battens will slip once the nails corrode leading to slumping and ultimately to stripping and repair.
In the present day, many thatchers will routinely strip an old roof completely so that new thatch can be fixed securely and efficiently to solid rafters using iron crooks. This stripping is almost inevitable when old straw roofs are rethatched with water reed, and very likely when older roofs are rethatched with one layer of new straw. In many cases, old rafters cannot be trusted to hold the iron crooks securely, so that the change from traditional 'long straw' to water reed or modern 'combed wheat reed' generally prompts major repairs or rebuilding. In the vast majority of cases this stripping is unnecessary, and owners and local authorities are persuaded to accept the change because of the mistaken belief that water reed lasts longer than straw. This may be the case on steeply- pitched roofs in drier East Anglia, but it is not the case on shallower roofs in wetter parts of the UK.
The evidence clearly shows that water reed thatching was rare throughout most of England. Straw, on the other hand, was ubiquitous, cheap and abundant, and a coat of good quality straw applied by a skilled thatcher could last for over 40 years.
Rethatching straw roofs with water reed or single-layer straw is responsible for most of the stripping of ancient thatch that is occurring on listed buildings. This change of material legally requires listed building consent, but many local authorities do not have even a basic understanding of thatching methods and give little importance to the 'thatch heritage' they are duty-bound to protect. Almost all examples of medieval thatch are at risk of being lost when the roofs in which they occur are next rethatched. Most of what survives will be lost within a decade if the destruction continues at its current rate.
Thatch through history
Most archaeologists agree that all early buildings in Britain, from the Neolithic until the late medieval period, were thatched. Direct evidence for prehistoric thatching, however, is almost non-existent. Much of the charred and waterlogged plant material recovered from archaeological excavations - such as the waterlogged remains of water reed found at Iron Age settlements on the Somerset Levels - could be derived from thatch, but a direct association has rarely been demonstrated in practice.
The best archaeological indicators for early thatch are probably the twisted, U-shaped split or roundwood 'spars' and notched pegs that have been used for centuries in Britain and Ireland to pin new thatch into place. Such fixings have undoubtedly been recovered from excavations, but appear in reports simply as 'sharpened stakes' with their role in thatching having been missed.
A thin layer of turf cut from the surface of a grazed bog or pasture was traditionally used as a base layer on thatched buildings in Ireland, and examples of such 'scraw' have been recovered during excavations of Viking-age buildings in Dublin and in the Shetland Islands. I have myself recently collected over 100 examples of scraw from derelict thatched buildings throughout Ireland.
High-status Roman buildings were tiled, but the dwellings and outbuildings of the populace were undoubtedly thatched. In England, thatching straw would have been obtained primarily from spelt wheat which replaced emmer wheat as the staple throughout southern England in the Iron Age. Later, invading Saxons brought continental thatching traditions to Britain from the reed-bearing coastal lowlands of continental Europe, along with a predilection for bread and beer made from common bread wheat and rye - the two principal components of medieval thatch.
Most early references to thatching date from the Norman period. The documents suggest that thatched towns were frequently devastated by fire, and authorities attempted to ban thatch, or reduce its flammability by demanding that roofs be coated with mud or whitewash. This rule was enforced with variable success throughout the medieval period, and thatch remained the most popular roofing material in both urban and rural areas because of its low cost and availability. Interestingly, a recent study of 200 years of the fire records of the Sun Insurance Company has revealed that thatched roofs do not catch fire more frequently than non-thatched buildings - although thatch fires are harder to put out once alight. Contrary to popular belief, a thatched roof is difficult to burn because the straw is tightly packed and often damp on the surface. This suggests that evidence for thatch on archaeological sites is much more likely to survive as a layer of humic material above a floor surface rather than as charred plant remains, even if the building in question was actually destroyed by fire.
A general decline in thatch began in the late 18th century, linked to the economic and social transformations of the ensuing century. Industrialisation, rural depopulation, enclosure of commons, drainage of wetlands, and scientific plant breeding leading to shorter, stronger- stemmed wheat varieties all influenced the availability of thatching materials. The expansion of the canal and rail networks brought cheap slate from Wales and Cornwall within the reach of many home owners for the first time.
The decline of thatch continued through the 19th and 20th centuries, and all but collapsed in the late 1940s and 1950s as a result of shortages of good quality straw, rising labour costs, the availability of cheap alternatives, and the loss of skilled craftsmen in two world wars.
A revival occurred in the 1960s, but with traditional 'long straw' thatch usually being replaced by water reed or 'combed wheat reed'. This has encouraged the widespread stripping of ancient thatch, and led to a catastrophic loss of six centuries of thatching history from thousands of buildings in just a few years.
John Letts is an archaeobotanist at the University of Reading
CBA web:Jan/Feb 2005