Geophysical survey methods allow for the detection of structures without excavation, using techniques such as magnetic gradiometry, electrical resistance or ground penetrating radar. At Olynthos, this serves two purposes: firstly, it has enabled us to make informed decisions about where to locate excavation trenches, since we already have an idea of the some of the features we are likely to encounter as we dig.  Secondly, and equally importantly, the survey data enable us to build up a picture of large areas of the city which we could not hope to excavate given the available time and resources, providing vital information about the kinds of buildings once located there, and about the way in which those buildings were arranged. We are using gradiometry and resistance survey which detect differences in magnetic susceptibility or conductivity due to the presence of varying subsurface materials (stone, soil, etc.). This has revealed anomalies which we interpret as the outlines of streets and buildings.

Electrical resistance survey

Geophysical survey has already clarified and changed our picture of the organization of the North Hill and the Lower City. It has shown that the urban grid on the North Hill continues in the unexcavated north-eastern area, although not quite as far as Robinson assumed.  It has also shown the course of the fortification wall on the eastern side. Finally, it has revealed detailed information about the plans of individual buildings, as well as offered indications of features such as large storage jars (pithoi) and also, potentially, industrial areas. In future work, we hope to locate and identify major public buildings and spaces within the grid-planned system, clarify the nature of the articulation between civic and residential quarters (road systems, defenses), and reveal the extent of the Lower City on its eastern side.

The settlement on the South Hill is much more poorly understood than that on the North Hill because less excavation has taken place there and because settlement is assumed to have developed organically over time on an irregular plan, in contrast to the grid-planned North Hill. We hope to explore the area using magnetometry and electrical resistance in the coming seasons of fieldwork.

Further reading about geophysics:
‘Archaeological Geophysics’ by Roger Sala, Ekhine Garcia and Robert Tamba (PDF)
Historic England guidelines to geophysical survey (PDF)
Archaeology Data Service Good Practices for Geophysical Data