In archaeological prospection, there are various methods employed to inform the discovery of archaeological sites such as ordnance survey maps, aerial photography, field walking, test digging and geophysics. Today we will be examining three forms of landscape prospection technique. Using the Stonehenge Riverside Project as a case study, I will illustrate how these techniques can be utilised to form a greater picture of the prehistoric landscape and inform where their excavations should be carried out. Additionally I will also highlight some of the benefits and limitations inherent to each by exploring each facet as it applies to the overall case study.
Employing a multidisciplinary approach to the interpretation of the landscape, the Stonehenge Riverside Project used a combination of new and traditional landscape archaeology techniques such as aerial photography, field walking and geophysics in order to determine where best to excavate (Parker Pearson et al. 2008). As Martin Carver states, “The techniques of landscape survey come in three main packages: looking at maps: cartography; looking at the surface of the ground: surface inspection; and looking from the air: aerial photography (Carver 2009, 65).” Having approached the Secretary of State for Culture, Media and Sport in order to get approval for the excavation, previous maps, aerial photography and plans of the site were used to great effect, allowing for a clear understanding of what needed to be done and what was hoped to be accomplished (Parker Pearson 2012). Building upon Julian Richards’ early work with the Stonehenge Environs Project in the 1980s, the Stonehenge Riverside Project is comprised of a team of archaeologists representing five different British universities, led by six academics from the discipline (Parker Pearson et al. 2008).
Figure 1. Hidden landscape features exposed through aerial view.
As illustrated by the Project’s initial approach, aerial photography (figure 1) is an excellent diagnostic tool in determining the potential archaeology of a site (Riley & Bewely 1996). Its greatest strengths, however are some of its utmost weaknesses, as it is highly dependent upon the conditions in which the images are being captured (Riley & Bewely 1996). Shadow sites are ideal for capturing early earthworks, soilmarks show in cultivated soil and cropmarks only show once the crop has begun to grow on a cultivated site (Riley & Bewely 1996). Additionally these indicators can be further affected by the soil conditions themselves, depending on how wet or dry, if clay is present or even how cold a site may be (Riley & Bewely 1996). Throughout the Project aerial photography was employed to highlight changes in the soil as well as understand the cut layers in a larger context (Parker Pearson et al. 2008). As illustrated by figure two, the ditches cut to form the circle of the Neolithic structures found south of Woodhenge are clearly distinguishable from the soil around it. This form of interpretative data could allow an archaeologist to draw conclusions about a site where no clear archaeological information is readily available.
Figure 2. Late Neolithic timber structures, amongst early Bronze Age ring ditches, south of Woodhenge.
In 2003, a combination of field walking and soil sampling was conducted (Parker Pearson et al. 2008). This was followed by a geophysical survey by English Heritage in the hopes of marking out specific features of ‘magnetic anomalies’ but the results were largely inconclusive or unclear apart from a ditch and a couple of particularly magnetic areas outside the eastern entrance of the henge (Parker Pearson 2012). Field walking is a type of sampling method employed on recently ploughed fields (Carver 2009). It is ideal for collecting artefacts scatters brought to the surface by the tilling of the soil (Carver 2009). Due to advances in analytical techniques, it has become possible to interpret the landscape, particularly in relation to depositional practices and how that impacts not only the spirit of place, but also how that affects memory (Parker Pearson et al. 2008). Therefore, an additional concern when approaching the landscape before any field walking was conducted, was the phenomenology of the landscape and the possibility that how it was transformed may have altered the perceptions of the peoples interacting with it (Parker Pearson et al. 2008).
Renfrew and Bahn explain phenomenology as “an approach that lays stress on the personal experiences of the individual or actor and on the way in which encounters with the material world and the objects within it shape our understanding of the world and hence our construction of our own world views (Renfrew and Bahn 1991).” When this method was employed by dividing the teams up into groups at fixed consistent 25 metre intervals along 50 meter transects, the Project was able to collect an assemblage of over 100,000 flint objects which allowed for an average sample to be projected across the entirety of the surface area (Parker Pearson 2012). While this proved to be a useful tool for the Project, it is not infallible, as early farmers often spread a variety of material, including pottery sherds, over their field when fertilising it (Carver 2009). As a result, field walking is often employed as an early diagnostic tool before more in depth prospecting methods are used (Carver 2009). It can also be argued that as it is an average sample, and the material in the ground could be contaminated through various external forces, it can give a flawed impression of material culture contained within the search area and beyond.
Unfortunately it is rare that an archaeological site will be able to be fully informed by either aerial photography or field walking alone (Greene 1983). While some details can be plotted, there are far too many variables affecting the interpretation of a site such as general lack of visible aerial evidence as described above, or mixed farming depositions with regards to field walking (Greene 1983). As a result, geophysics becomes an ideal prospecting method, as it is highly efficient and can allow the archaeologist to explore a site at depth with little or no direct intervention (Greene 1983). Although typically performed on a much smaller scale due to general time and funding constraints, modern advances with computers and survey systems has allowed for information to be processed and printed on site as the survey is carried out (O’Connor & Evans 1999). Geophysics is divided up into three primary survey methods: earth resistance survey, magnetic survey and electromagnetic (EM) survey, the latter of which is comprise of a range of techniques combined into a larger EM system (Linford 2006). The first contemporary method to be developed was earth resistance survey (Linford 2006). Ideal for most archaeological field conditions, it is limited by its reliance on objects to be near to the surface in order to distinguish it from the soil (Linford 2006). Magnetic survey is the most heavily used prospecting tool in the discovery of archaeological finds (Linford 2006). This is largely due to its ability to detect even the most elusive archaeological features as well as the capability to employ it easily over a large scale landscape while acquiring data rapidly under the appropriate conditions (Linford 2006). Collectively, electromagnetic techniques are often referred to as GPR, or ground penetrating radar (Linford 2006). GPR is most effective due to its flexibility (Linford 2006). Unlike its contemporaries, GPR can function over a variety of solid surfaces, making it especially advantageous in urban environments (Linford 2006).
While initial prospecting was conducted by magnetometer and resistivity survey, it was ultimately GPR (figure 4) that was employed throughout the excavation (Parker Pearson et al. 2008).
Figure 4. GPR Map of the Neolithic Landscape.
While initial geophysical survey led to the discovery of various anomalies below the soil, which could indicate some form of henge or mound within the landscape of the Southern Circle, it was not until the area was excavated that it revealed that it was in fact the remnants of a former chalk quarry protecting the remains of a Neolithic house (Pearson 2012). Unfortunately geophysics is not without its issues either, as discovered by the Project, as the initial survey had significant difficulty locating any features below the soil (Pearson 2012). When the Project team returned to the Southern Circle two years later, they discovered that they were unable to get adequate readings of the remaining landscape features (Pearson 2012). As a result the project team had to remove a metre of top soil in order to achieve a decent level of resistivity in order to produce a readable result (Pearson 2012). It then became possible to create a full plan including the postholes of the Neolithic houses that had been constructed in circles on that part of the site (Pearson 2012). When GPR was later introduced at the Durrington Walls henge site (Figure 5), it allowed for the revelation of “two formerly unknown blocked entrances through the henge bank, and the causeway character of the ditch, indicating that this was probably dug in sections by a series of work-gangs (Parker Pearson et al. 2008, 156).”
Figure 5. GPR results of the Durrington Walls excavation.
As a result of the subsequent survey and excavation carried out at Durrington Walls, the Project was able to surmise that the henge site not only served a contemporary purpose, but was also constructed to a similar scale and layout to Stonehenge and it was highly likely they were perceived as linked by the river between them, making the combined landscape a single site (Parker Pearson et al. 2008). This interpretation owes much to the phenomenological approach initially taken on the site, and therefore it can also be argued that the results justify the decision to consider it in the first place. Ultimately it was the combination of survey techniques and methods that enabled this site to be fully explored and informed. Without such a multidisciplinary approach, such an in-depth view of the Neolithic landscape would not have been possible, however it is still not a complete picture and this could be due as much to the limitations of these techniques as the technologies that support them. It is highly likely in years to come, as the these technologies become more refined and more advanced systems become available, future archaeologists will be able to interpret the landscape in a greater depth than has been achieved by the Stonehenge Riverside Project team. In conclusion while there is perhaps no right or wrong way to go about site prospection prior to an excavation, it is clear that a multidisciplinary approach lends itself to the greatest results.
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- Parker Pearson, M. Pollard, J. Richards, C. Thomas, J. Tilley, C. Welham, K. The Stonehenge Riverside Project: Exploring the Neolithic Landscape of Stonehenge. Documenta Praehistorica XXXV. 2008 UDK 903 – 7 (410) “634”
- Parker Pearson, M. 2012. Stonehenge: Exploring the Greatest Stone Age Mystery. London: Simon & Schuster
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- Riley, D.N. and Bewely, R. 1996 Aerial Archaeology in Britain. Princes Risborough: Shire
- Figure 1. Stonehenge Riverside Project: http://i.ytimg.com/vi/ex3ciqDuJqA/0.jpg
- Figure 2. Stonehenge Riverside Project: http://i.ytimg.com/vi/ex3ciqDuJqA/0.jpg
- Figure 3. http://www.wessexarch.co.uk/system/files/images/fieldwalking_near_stonehenge.jpg
- Figure 4. http://www.bbc.co.uk/news/science-environment-29126854
- Figure 5. http://www.bbc.co.uk/news/science-environment-29126854