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Silchester Iron Age Environs Project: Aerial Photo and Lidar Investigation and Mapping

The aerial survey component of the Silchester Iron Age Environs Project is making remarkable new discoveries in the landscape around the long known Iron Age oppidum and Roman town of Calleva. The focus of the project is investigation of the Pre-Roman Iron Age, but the survey is finding evidence of landscape change dating from the later prehistoric period up to the Second World War.

Examination of aerial photographs and lidar imagery is just one method experts from the University of Reading project team and Historic England are using to look at the landscape form the Thames Valley to Basingstoke. From the air, sites appear as 'earthworks' and 'cropmarks/soilmarks'. By 'earthworks' we mean sites which are at least in part extant above the ground. 'Cropmarks/soilmarks' are terms archaeologists use to describe the surface indications of buried archaeology. These are visible as changes in colour and height in a crop or bare soil.

Other non-intrusive techniques include:

Experts will use the results to identify areas for further investigation including excavation and environmental analysis.

Greyscale lidar image showing a large banked enclosure with smaller subdivisions sitting within modern fields
Silchester Roman town as seen in a lidar derived image, using a hillshade visualisation of the Digital Terrain Model (DTM) © University of Reading: Source Environment Agency

Silchester - A regional centre for the Atrebates

The Iron Age oppidum and later Roman town of Calleva is probably the most intensively studied feature in the project area. There is a system of dykes around the Iron Age oppidum, frequently surviving as upstanding earthworks. The Roman town sits within a network of roads, which survive in part as earthworks or sub-surface deposits evident as cropmarks.

The survey results have shown evidence of settlement across the project area, probably from the Bronze Age through to the Roman period. It has also identified sections of the Roman roads, including a previously unrecognised section of the road from Calleva to Verulamium. Evidence of later land use includes medieval moated sites and deer parks, medieval and post medieval field systems, post medieval country parks and extensive 20th century military sites.

Landscape in transition

The results of the aerial survey show how settlement patterns and land use changed over time. The survey has identified probable later prehistoric settlement sites, often consisting of circular or oval enclosures, around Silchester. Examples include two enclosures visible as cropmarks on aerial photographs to the south of Mortimer and three possible settlements within Pamber Forest.

Colour vertical aerial photograph showing arable fields with archaeology seen as dark lines against a paler background
Two enclosures to the south of Mortimer which may be Iron Age in date. Google Earth: Image © Getmapping
Greyscale lidar image showing  several small sub-circular enclosures in a landscape of tracks and paths
Three possible later prehistoric settlement enclosures within Pamber Forest, as seen on lidar derived imagery, a hillshade visualisation of a Digital Terrain Model (DTM) © University of Reading: Source Environment Agency

Different types of settlements emerge later in the Roman period, which may tell us something about how society was changing. They appear as rectangular ditched enclosures, either found on their own or in ladder-type groups. To add to this picture of changing patterns of settlement, the survey identified cropmarks to the south of Calleva. These may be the remains of a large villa complex or settlement.

Colour map extract showing
Ladder-type settlement, possibly a farm complex, at Ufton Nervet in the northern part of the survey area. Later field boundaries overlie the settlement. © Crown Copyright and Database Right (2016) OS (Digimap Licence)

It is less clear where the food for these settlements was coming from. The survey found only a few fragments of the field systems that may have been associated with them throughout the survey area. An example is the cropmarks on 1930s aerial photographs (taken by OGS Crawford) to the north of Calleva, which appear to have been completely removed after this time. Recent geophysical survey produced no results for this area and the field boundaries are not visible on later photographs.

This probably shows that while the landscape use is relatively static today, this area has seen the effects of agricultural intensification in the past, probably in the post-Second World War period.

Black and white vertical aerial photo showing arable and pasture fields with woodland to one side
Very faint traces of later prehistoric field boundaries can be seen on this photograph taken on 11 May 1934 (NMR CCC/9107 09440) © NMR Crown Copyright - Crawford collection

Land use appears to have changed considerably in the medieval period and areas where people were living in earlier times are now covered by woodland and parks. Pamber Forest covered a larger area than today and there are examples of deer parks in many areas including Silchester, Beaurepaire Park and The Vyne. The last two examples were later developed into 18th century landscape parks around large country houses.

Military sites in the Silchester landscape

Development of large areas of land for military use had a significant impact on the landscape around Silchester from the First World War onwards. Many continue to be Ministry of Defence sites. Wartime and later aerial photographs reveal the way that these military sites develop and change over time.

The Bramley military training area covers an area of approximately 600 hectares either side of the Reading to Basingstoke railway line. It was first used during the First World War as an ordnance depot which expanded during the Second World War. A series of spurs led off the railway into different areas of the depot. In the post-war period it became a military training site.

The Second World War Aldermaston airfield, later the Atomic Weapons Establishment (AWE) is on the western edge of the survey area. It is now associated with another extensive military site within the Silchester environs zone, the Burghfield Royal Ordnance Explosives Filling Factory. The factory began production in 1942 and was reconstructed in 1953 as part of the AWE.

Black and white vertical aerial photo showing large complex of buildings laid out on a regular grid of roads
Burghfield Royal Ordnance Explosives Filling Factory photographed by the RAF on AF 106G/UK/1646 3201-2) Historic England RAF photography

The Bramley ordnance depot proved not to be the only place storing munitions in the Silchester area. Careful examination of aerial photographs from the 1940s identified many regularly placed groups of what seemed to be small rectangular structures within Stratfield Saye Park, Beaurepaire Park and in many areas of woodland. These structures are in fact piles of munitions stored in dispersed groups across large areas of countryside.

A curious group of cropmarks appears on recent aerial photographs, indicating the buried remains of a large complex of buildings and boundaries at Stratfield Mortimer. Historic maps do not show anything to suggest what the site might have been and at first glance, this could have been a major Roman site. This interpretation seemed unlikely, however, given all the previous work in the area. The fact that the project is examining all aerial sources from the last 50 years solved this puzzle. RAF photographs show the area in 1946 when this was the site of a Second World War Prisoner of War Camp.  Officially known as Camp 88, the site was a German work camp, where prisoners were sent to work as labourers in the local area. The buildings were removed after the war, but the traces of their foundations still affect the growth of crops above them.

Black and white vertical aerial photo showing a regular arrangement of buildings set within a perimeter with fields around
Prisoner of War Camp 88, Mortimer, as photographed on 10 July 1946 (RAF 106G/UK/1647 5028) Historic England RAF photography

The images used on this page are copyright Historic England unless specified otherwise. For further details of any photographs or other images and for copies of these, or the plans and reports related to the project please contact the Historic England Archive.

 

Colour photograph of man in a hat

Simon Crutchley

Remote Sensing Development Manager

Simon is a landscape archaeologist and air photo interpreter at Historic England, with over 25 years’ experience of mapping and interpreting features of archaeological and historical interest visible on aerial photographs and other aerial imagery. He has worked in many areas of England including the World Heritage Sites of Avebury and Stonehenge. He has a special interest in “new” technology such as lidar and satellite imagery and its application to archaeological research and investigation.

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