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Aerial Archaeology in Essex

essex.jpg - 5049 BytesWhile both CUCAP and the RCHME have carried out reconnaissance in order to record upstanding architectural monuments and cropmark sites over Essex, a number of local archaeologists, notably Ida McMaster and Captain R. H. Farrands, have also flown for this purpose. In addition, in the 1970s, the then county archaeologist J. Hedges began to carry out occasional sorties in order to record cropmarks and excavations. This led to the establishment of a coherent programme of annual reconnaissance in the 1980s. Many of the photographs reproduced here result from aerial survey, partly funded by the RCHME, carried out by the Archaeology Section of Essex County Council. Copies of all of these photographs, and many others, are held in the county Sites and Monuments Record (SMR), a public record which is maintained by the Archaeology Section of the County Council.
The Archaeology Section of the County Council is currently carrying out the Essex Mapping Project, which is part of the RCHME's National Mapping Programme. The project, which in Essex began 1993 and is funded by the RCHME, has the basic aim of mapping, at a scale of 1:10,000, archaeological and historical information visible on aerial photographs. Cropmarks, soilmarks and earthworks are mapped using set conventions, from both available vertical and specialist oblique photographs from a number of sources. Information about the morphological nature of mapped features is then compiled onto a computer database which will allow sites with similar characteristics and topographical setting to be extracted and their distributions plotted. By comparing excavated sites with groups of similar sites identified by the database, it is hoped that archaeologists will be able to make more informed interpretations about the nature of the sites which appear on photographs.
The development of satellite imagery over the last few decades, indicates the enormous technological leaps which have occurred since the early balloon photography carried out only a hundred and fifty years ago. It also attests, however, the continued desire to witness the earth from the aerial perspective, allowing us not only the ability to record the current state of affairs, but to monitor change over time.
In recent years, pioneering work in Essex has helped to develop the use of aerial photography along the coast, and in particular, on the extensive inter-tidal mud-flats. Flying along the coast at low tide, timber fish-weirs, oyster pits, shipwrecks, and hulks of other boats have been recorded in this way. Many of these areas are extremely inaccessible, and aerial photography allows archaeologists to rapidly cover large areas and locate structures which they can then visit on foot.
The appearance of cropmarks are particularly important in Essex for a number of reasons. Almost all of the remains of prehistoric human activity have been levelled by later agriculture, unlike upland areas of Britain, where prehistoric burial mounds and forts survive as earthworks which can be viewed on the ground. Indeed, with around 50% of the total land-use of the county dedicated to arable cultivation, it is clear why the occurrence of cropmarks is important to archaeologists in Essex. The geology of the county also plays an important role, however, as the gravels and sands which are common along the river valleys and coastal plains, are self-draining. This results in moisture in the topsoil draining away through the gravel, unlike heavier soils, such as clay, where moisture is more likely to be retained. The greater differences between the moisture content of the archaeological features and the surrounding soil results in more defined cropmarks. In particular, Tendring district, the Thames terraces and the Chelmer valley are very productive in terms of cropmarks, although in conditions of extreme drought, the boulder clay areas also produce cropmarks which most years never form. Indeed, it is possible that if the current trend of climatic change continues, tending towards longer, drier summers, the heavier clay areas may begin to produce significant numbers of previously unrecorded sites.
Over the last fifty years, the recording of cropmark sites has radically altered our understanding of the extent and complexity of archaeological landscapes in many parts of the country. Many new sites, however, continue to be discovered on an annual basis. Archaeologists must record these sites whenever possible as their appearance lasts only until the crop is fully ripened. While many sites may reappear year after year, some will appear only in the driest conditions, and then may lie under a non-cereal crop which may not produce a cropmark. In addition, continual ploughing, and modern deep ploughing in particular, can erode the buried archaeological sites which cause the cropmarks to form. It is important, therefore, that archaeologists continue to record sites from the air, not only in order to discover new sites, but also because it presents a rapid and efficient method of monitoring land-use changes and other developments which may threaten archaeology.
Mapping and Interpretation
Once archaeological features have been recorded on aerial photographs, they must be mapped in order to understand their relative shape and size. The position, shape and size of cropmarks are plotted onto modern base maps by comparing the position of objects, such as buildings and field boundaries, which appear both on a photograph and the relevant map. This is especially necessary with oblique photographs which are taken at an angle from the aircraft. The perspective distortion of features on such photographs requires rectification in order to appreciate a site's actual shape. The resulting cropmark plots can be studied either on a site specific, detailed level (i.e. at a scale of 1:2,500), or by viewing a number of sites over a larger area of land (around 1:10,000 or more). This allows comparisons to be made between individual sites and provides information about the position of sites relative to each other, and the natural landscape.
Often cropmarks represent the remains of several periods of history which are built over each other and subsequently levelled by ploughing. In these instances, it is necessary for the interpreter to identify individual elements which are contemporary, usually on the basis of form and orientation. It is then possible to suggest how use of the landscape has developed over time, without excavation. Cropmark interpretation can often call upon other sources of information, such as old maps, place-names or records of artefact finds, which may suggest or support the interpretation of what a particular cropmark might represent.
The study of the shape and size, or morphology, of cropmarks is used in order to suggest the date and function of cropmark sites with particular shared characteristics. The many different shapes and sizes of enclosures which appear as cropmarks, for example, can be studied and similar groups can then be compared with examples which have been excavated and which archaeologists understand. It can then be assumed that enclosures of similar size, shape and with a similar position in the landscape, might have a similar function and be of similar date. The distribution of these enclosures can then be studied in relation to rivers, soils and other archaeological sites in the area. While cropmark plots can be seen as maps of prehistoric, Roman and medieval activity, to aid the study of the archaeology of the county, they are also used to inform archaeologists when sites are threatened by modern developments such as roads and housing.
th1.jpg - 4011 BytesBeaumont Otes, Chignall: The cropmark shows very clearly the outline of a moated homestead with small annexes, possibly gardens, and associated trackways and field boundaries. The field has produced finds of late Medieval pottery and tile, and a map of 1599 shows the site surviving and named "Beamond Moates", explaining the corruption to the modern place-name. While the site had appeared as a faint cropmark in 1979, this photograph, taken in the very dry summer of 1995, appears to have caught the differential growth of the crop at its optimum, affording very good detail. Indeed, a network of very fine polygonal features, caused by frost action during the last Ice Age, is also visible. (photo: D. Strachan; copyright: Essex County Council).
th2.jpg - 5252 BytesTilbury Fort on the River Thames: A blockhouse was originally built here under Henry VIII, in 1539-40, as part of a larger system of defence against enemy fleets. Late 16th century refurbished was accompanied by an a surrounding rampart and ditch, however, this was replaced in 1660 when Charles II ordered his chief engineer, Sir Bernard de Gomme, to construct a new fort, which is largely visible here. Built between 1670-82, after a number of designs had been submitted, much of the surviving defences, such as the outer glacis and inner moat, date from this period. Various minor alterations and additions were carried out throughout the 18th century, including the addition of two massive powder magazines, storehouses and barracks. The fort also briefly served as a prison for Jacobite highlanders captured after the battle of Culloden in 1746. During the invasion threat of the Napoleonic war, however, ten armed hulks were manned between Tilbury and Gravesend as an additional defence. (photo: D. Strachan; copyright: Essex County Council).
th3.jpg - 5906 BytesHulks at Maldon: The remains of these boats, recorded at low tide on the exposed coastal mud-flats, have been identified as the dismantled as burnt out remains of a number of Thames barges, including the British Lion, a 43 ton vessel built at Rochester in 1879; the 80 ton Mamgu of London; the Pretoria, a 54 ton vessel constructed at Faversham in 1902; and the William Cleverly, a 46 ton barge built at Rochester in 1899 and re-rigged in 1960's before being broken up at Maldon promenade. While the eroding hulks of wrecks are a common site on the Essex coast, such sailing craft are no longer built, and many of the techniques of construction could be lost if they are not recorded in detail. Aerial survey allows a rapid and cost efficient method of locating sites prior to more detailed study. (photo: D. Strachan; copyright: Essex County Council).
th4.jpg - 1735 BytesSaxon tidal fish-trap, Sales Point: Tidal fish-traps are known in many forms from across the world, and have been used since the prehistoric period. These are barriers of timber or stone which are designed to guide the movement of fish into baskets for collection. They are often V-shaped, and positioned so that fish are channelled into the trap, or "eye", as they drift out with the falling tide. A number of large, timber-built fish-traps exist on the mud-flats of the Blackwater Estuary, and these consisted of upright posts with wattle fencing and baskets at the "eye". The large, roughly rectangular fish weir at Sales Point, measures over three hundred metres in length and was probably designed to catch fish on both the flood and ebb tides. This trap is only exposed by the lowest of tides of the year, which often occur early in the morning as indicted by the haze caused by the sun-rise on this photograph. When in use the traps would have been exposed at all low tides, indicating sea-level rise since they were in use. This trap was recently C14 dated to the late-7th to the 9th centuries, or the Middle Saxon period. (photo: Steve Wallis; copyright: Essex County Council).
th5.jpg - 5110 BytesPossible Long Barrow, Mount Bures: This open ended elongated enclosure is situated on the valley floor of the river Stour (the river running to the left of the frame). The line of pits along the north-east facing ditch was first recorded on this photograph from 1996, and as yet has no parallel in the county. It is possible, however, that the lines result from quarry ditches of an earthen long barrow, and that the pits supported timber posts of a structure covered by the mound. Long barrows often contained the disarticulated skeletons of a number of important people from the local Neolithic communities. It seems likely that the bodies of the dead were exposed to the elements prior to internment, possibly on platforms, and it has been suggested that this would have occurred inside long mortuary enclosures. The river, which now forms the boundary between Essex and Suffolk, was the focus of an extensive prehistoric ritual landscape consisting of concentrations of barrows. The two ring-ditches, seen at the bottom of the frame, are part of a concentrated cemetery consisting of ten barrows. (photo: D. Strachan; copyright: Essex County Council).
th6.jpg - 7513 BytesThe Waltham Abbey Royal Gunpowder Mills: Gunpowder production in the area began in the 16th century, and the site was bought by the government in 1787. The 19th century saw the extensive construction of buildings and canals, which allowed barges to transport explosives smoothly so as to limit the risk of explosion. English Heritage have described Waltham Abbey as "the most important site for the history of explosives in Europe", and, following recent recording of the site, a heritage centre is planned. The photograph shows the South Site, constructed in the 1880's during the shift to chemically based products. The image shows 44 rectangular drying stoves, surrounded on three sides by a blast containing earthworks. This group of widely spaced buildings (another measure against unwanted explosions) was connected by a canal network which linked them to the North Site. These were then replaced by tramways and then roads, all constructed on the same lines. South site was demolished in 1998 and is to be developed as a residential complex. Aerial images such as these record the landscape prior to such huge changes. (photo: D. Strachan; copyright: Essex County Council).
th7.jpg - 4135 BytesBronze Age Barrow Cemetery, Brightlingsea: The photograph shows the buried circular ditches of twenty-two barrows which resulted in cropmark formation in previous years. The top soil has been removed to allow archaeologists to excavate prior to destruction of the site by gravel extraction. Situated on the Brightlingsea peninsula of the Colne estuary, excavations proved the cemetery to consist of numerous ring-ditches, which presumably surrounded barrows, and numerous cremation urns buried in pits in between the barrows. Cemeteries of this kind, with very dense clusters of ring-ditches, are characteristic of north-east Essex. A multi-period cropmark complex to the east of the cemetery may contain the remains of a related settlement site. (photo: Pete Rogers; copyright: Essex County Council).
th8.jpg - 7475 BytesEnclosures and related field systems near St. Osyth: While numerous cropmarks are visible on this photograph, the main feature is the large sub-rectangular enclosure at the bottom of the frame. it has an annexe to the left, and a series of related field systems below and above. The enclosure also contains two ring-ditches, which may represent hut drainage gullies. The field-systems would have contained fields for arable cultivation and paddocks to contain animals, and these are laid out in a similar orientation to the enclosure, suggesting that they are of similar date. This early agricultural landscape, laid out in a rectilinear pattern and orientated NW-SE, was already in existence prior to the building of the main Roman road from Colchester to Clacton. A large ring-ditch of probable Bronze Age or Neolithic date, is also visible below the corner of the caravan park, indicating that this coastal plain was continually a focus of human activity throughout the prehistoric period. (photo: D. Strachan; copyright: Essex County Council).
th9.jpg - 5911 BytesPewit Island, Langenhoe: This remote salt-marsh island contains the remains of the extensive oyster cultivation industry which existed along the coast. Oysters were wintered in the rectangular pits, visible cut into the salt-marsh. The small building is a timber-built "packing shed" where the oysters were packaged prior to transportation in sailing "smacks", a type of regional sailing craft. Pits are also often found cut into salt-marsh along the outside of sea-walls. By the 19th century large companies, such as the Colne Fishery Company and the River Roach Company, had developed in addition to individual dredgers and tenant workers. The zenith of the mid-19th century saw oysters considered as the common food of poverty-stricken Londoners. Within decades, however, poor harvests, resulted in their being regarded as an expensive delicacy. The introduction of foreign species, intended to boost production, also resulted in the introduction of new pests which became a problem, however. A number of reports were then published which indicated health hazards caused by oyster cultivation near sewage outfalls, and the consumption of oysters was linked to widespread out-brakes of cholera and typhoid. Oysters are now produced in the Blackwater estuary without such problems. (photo: D. Strachan; copyright: Essex County Council).
th10.jpg - 5279 BytesRed Hill near Tolleshunt D'Arcy: Over three hundred Red Hills, the remains of prehistoric and Roman salt making sites, are found along the Essex coast. Before electrical refrigeration, salt played a crucial role in the preservation of meat and fish and a very valuable commodity. In Essex, the sea provided a great resource for salt and many of those who lived along the coast would have, on a seasonal basis, be involved in extracting salt from sea-water. The sun would evaporate sea-water trapped in open pans cut into the water-tight clays. This concentrated brine was then boiled in rough ceramic vessels until all the water was removed and only the salt remained. The crudely-made vessels, known as briquetage, and are found in large quantities at the sites, and, along with the burning process, result in the red soil which makes of the mounds of debris. This site is now situated in eroding salt-marsh outside the modern sea-wall, and inspection on the ground shows that layers of broken briquetage survives above layers of charcoal, the remains of ancient fires. (photo: D. Strachan; copyright: Essex County Council).
th11.jpg - 8480 BytesSaltmarsh at Fingeringhoe: Perhaps one of the most interesting yet delicate environments along the Essex coast, mature saltmarsh expanses such as these are continually eroding as result of sea-level rise and the existence of sea-walls constructed to reclaim land in the Medieval and Post-Medieval periods. While this area of marsh has never been reclaimed, it was still used as grazing marsh for sheep, as indicated by the pathway running across the marsh. (photo: D. Strachan; copyright: Essex County Council).
Further Reading:
  • Bayliss, T. and Owens, S. (ed)1990 Britain's Changing Environment From The Air, Cambridge University Press.
  • Bewley, R. 1994 Prehistoric Settlements, Batsford, London.
  • Glasscock, R. (ed.) 1992 Historic Landscapes of Britain From The Air, Cambridge University Press.
  • Riley, D. 1982 Aerial Archaeology in Britain, Shire Archaeology, Princes Risborough.
  • Strachan, D. 1998 Essex from the Air, Essex County Council, Chelmsford.
  • Wilson, D. 1982 Air Photo Interpretation for Archaeologists, Batsford, London.
Contact Address:
Davy Strachan, Essex County Council, Planning Department, County Hall, Chelmsford, Essex, U.K.
The above text and photographs are taken from "Essex from the Air", by Davy Strachan, which was published in 1998 by Essex County Council. This full-colour, 110 page, book features photographs taken by the Essex County Council, the RAF, Cambridge University and the Royal Commission on the Historical Monuments of England.
The book is available (at 15 including postage and packaging) from Roger Massey-Ryan, Essex County Council, Planning Department, Archaeology Section, County Hall, CM1 1LF (tel: 00 44 1245 437633). Payments in Sterling, please, Eurocheques are acceptable. or contact
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