Aerial Investigation and Mapping in the Stonehenge World Heritage Site
Historic England’s Aerial Investigation and Mapping Team’s recent re-survey of the entire Stonehenge World Heritage Site (WHS) ‒ not only the area south of the A303 ‒ used aerial photographs and lidar, and showed that previously unrecognised sites are just as likely to be spotted on historic photographs as on the latest digital imagery.
The main aim of the 2016 re-survey was to reassess and update the results of an earlier project – the Stonehenge WHS Mapping Project of 2001 – in the light of imagery that has become available since its completion. This chiefly comprised new aerial photographs taken in the course of Historic England’s annual aerial reconnaissance programme , newly accessible aerial photographs taken prior to 2001, and lidar (airborne laser scanning).
The 2001 survey resulted in a 26 per cent increase in the number of known sites in and around the WHS. Since then, of course, a considerable amount of fieldwork and research has focused on the area. Nonetheless, the 2016 survey identified previously unrecognised features. This point is worth emphasizing – no survey can ever offer the last word on a particular landscape.
None of the features identified in 2016 are particularly spectacular on their own, but together they add considerably to our knowledge of the Stonehenge environs as a whole, enhancing our ability to piece together the long-term history of the landscape.
Most of the new detail – which ranges from prehistoric barrows to 20th-century military sites – came from the newly accessible historic photography. No significant features were found with the lidar, although this technique contributed useful detail to previously known sites. For example, the slight earthwork traces of low, eroded field banks have added to our knowledge of some of the extensive later prehistoric field systems mapped by earlier surveys, although in too many cases there was little still surviving above ground by the time lidar was first flown in the area. On the whole, this is not the ideal landscape for lidar. Relatively open, it has been subject to a considerable amount of intensive arable agriculture over the years, while more than three centuries of fieldwork mean that hundreds of sites – some no longer visible on the surface – have already been identified.
The kind of spectacular results achieved elsewhere, such as on the South Downs were never going to be matched here.
Newly identified sites
The ‘new’ sites varied considerably in terms of period and type. Particularly noteworthy was the identification of around 20 potential Bronze Age round barrows such as the one illustrated below, which was spotted on a 1943 US Air Force vertical photograph. The rectangular plantation, which is a few hundred metres south-east of Stonehenge, conceals Amesbury 16, a known Bronze Age round barrow. The dark circle just to the north of the plantation may represent the trace of a ditch which once surrounded another such burial mound. Amesbury 16 has been known since at least the beginning of the 19th century, so if there was once a mound within this new feature, it had disappeared by then.
The value of historic aerial photographs is abundantly clear on examples such as that shown below, an extract from another World War II vertical photograph. The extract shows part of the military camp at Larkhill, located a short distance north of Stonehenge. The low, clear winter sunlight, shining from the south-east, allows even the slightest of features to cast a shadow, thereby enhancing their visibility. Almost all of the upstanding features are military buildings of various ages, sizes, materials and functions; few of them were intended to be permanent, or even long-term, fixtures. In some cases, these photographs may be the only surviving documentary record of a site’s existence.
Visible among the standing buildings are the faint surface traces of previous structures, particularly evident from their tendency to conform to the grid layout of the camp, as well as in other regularities of their size, shape and arrangement. Running across the open spaces in the centre of the photograph is a less regular grid-like pattern of slight earthworks following a markedly different alignment. This represents the then-extant remains of a prehistoric field system of Bronze or Iron Age origin. Today there appears to be no surviving surface trace of these features. As well as the prehistoric field system, a series of circular features representing a Bronze Age barrow cemetery can be seen just left of centre. These barrows still survive, and are protected from both military and agricultural activity.
There are several blocks of prehistoric fields, similar to those in the above photograph, located in and around the WHS. In most cases they have suffered considerably from 20th-century ploughing, but there are a few places where there are still hints of above-ground survival. For example, in the photograph below, taken in 2012, slight shadows mark the locations of heavily plough-truncated field boundaries. The photograph shows the area between the A360 (right) and the Diamond Plantation (left), south of the Winterbourne Stoke crossroads (just out of shot to bottom right). In amongst the fields is a circular feature previously recorded as a possible Bronze Age round barrow, though historic aerial photographs show it clearly as a hollow rather than a mound and early maps record a dewpond approximately at this location. The field boundary dividing the pig farm (bottom left) and the wood from the arable fields is an earthwork of later prehistoric origin related to the adjacent field system.
A possible round barrow
Another instance where historic – again, wartime – photographs helped interpret a recently-identified feature also concerns a circular cropmark. Photographs taken during a reconnaissance flight in August 2010 captured traces of a small, dark ring in the grass close to the sites of two known Bronze Age round barrows. In the first image below, the grassy mound is the barrow known as Amesbury 23, and the dark circle beneath it is the ditch of Amesbury 23a. The small dark ring to the right of Amesbury 23a is the feature first seen in 2010 (the circular worn patch on the extreme right is the former site of an animal feeding trough). Could this ‘new’ ring represent a previously unsuspected barrow?
In fact the 1943 coverage showed that the location of this feature coincided with the foot of a wartime radio mast, visible on the photograph mainly via the shadow it cast. The mast sat within a square fenced enclosure, with a control building nearby.
Overall, the re-survey of the Stonehenge WHS and its environs confirms the complex and varied nature of this landscape’s history, as well as emphasizing the fact – perhaps not as fully appreciated as it should be – that there is far more to the landscape than the familiar Neolithic and Bronze Age ceremonial and funerary monuments. A full report is in preparation, and will be made available as part of the Historic England Research Report series.
Martyn Barber has worked in Historic England and its predecessors since 1990, moving to the aerial survey team in 2002. Most recently he has worked on the (recently published) Stonehenge Landscape Project. He is a Senior Investigator in the Historic Places Investigation Team.
Photograph copyright Sarah McCarthy
Fiona Small is an Investigator in the Historic England’s Aerial Investigation & Mapping section of the Historic Places Investigation team. She joined the Royal Commission on the Historical Monuments of England in 1992, trained as an air photograph interpreter, and subsequently worked as an aerial investigator for both English Heritage and Historic England. She has been involved in a number of major National Mapping Programme, multidisciplinary and multi-period projects. Fiona has particular interests in 20th-century military archaeology, and in the contribution aerial archaeology can make to understanding historic landscapes and the evidence for the continuity of human activity through time.