But what if there isn't any trenches? In sweden, a large percentage of graves consist of single burial layers on top of the original top soil. How easy are these burials to identify?'
Archaeological prospection based on non-invasive near-surface geophysical measurements or remote sensing techniques (e.g. aerial photography) may show structures in the data that are anomalous compared to what you would expect if the soil would me more homogeneous than it actually is - so called
anomalies.
Depending on the size, shape, orientation and strength of an anomaly and its relationship to possible other anomalies in its vicinity, comparative data from already excavated (ground-truthed) similar anomalies and knowledge about the character of buried structures expected to be found in the area, one can attempt an interpretation of the data. Anomalies can be of natural origin (showing changes in near surface geology, soil formation processes or bioperturbation) or manmade. In case of anomalies caused by manmade structures we are interested in those that are of prehistoric origin (aside from all the utilities, drainage trenches and other rather recent soil disturbances).
Frequently we are able to identify pits in the data. Pits can have been dug as postholes, cooking pits, Grubenhäuser, waste pits, latrines, graves, and more.
In case of the test in Norway the context of the pits (proximity to burial mound, find of cremated human bone on surface) permited their identification as graves, irrespective of the trench or any other demarcation line surrounding the central burial (overploughed mound). Most burial mounds that I have come across so far either show a small surrounding trench or circular stone setting at their foot (foot chain). Such a circular delimitation and a central rectangular stone packing visible in the ground penetrating radar data measured in 2010 permitted the identification of the grave discovered outside Uppåkra church yard. The predicted structures were subsequently confirmed in great detail by archaeological excavation (see images 001, 011 and 012 in the latest
Uppåkra folder; fig. 012 is rotated 90 degrees clockwise compared to fig. 011).
While it is most times impossible to identify an isolated grave pit as such from prospection data alone, when occurring in larger numbers (aka grave field) they can be identified by their size, orientation, relative positioning and difference in character when compared to other anomalies caused by settlement structures.
In order to gain data that may permit the archaeological interpretation of the observed anomalies it is of great importance that large areas are covered: you need to be able to see the boundaries and variations in anomaly density. While small surveys may show some individual anomalies, their interpretation will often not be possible. At Uppåkra we have covered some 175 hecatres with magnetics and a dozen hectares with GPR, Sweden's largest archaeologically prospected site so far.
