Groundbreaking without breaking ground
- DATE WRITTEN:
- READING TIME: 3 minutes
- AUTHORS: Candice Wachtel and Sophie Walker (Assistant Community Engagement Archaeologists)
There are many ways in which archaeology incorporates scientific methods and principles to aid our investigations such as radiocarbon dating, isotope analysis and aDNA to name but a few, but before all of that, before we even put a spade (or machine bucket) in the ground, one particularly versatile area of study can make a world of difference: geophysics.
Geophysics in archaeology refers to a suite of non-invasive scientific techniques that allow archaeologists to detect, map, and interpret buried features without excavation. These methods measure subtle variations in the physical properties of the ground, such as magnetism and electrical resistance, to reveal traces of past human activity.
One of the most widely used techniques is magnetometry. This method measures tiny changes in the Earth’s magnetic field caused by features in the soil. Past human activities such as digging ditches, lighting fires or filling pits can disturb the natural magnetic properties of the ground. Over time, these disturbances create detectable magnetic contrasts.
During a magnetometry survey, an archaeologist walks systematically across a field carrying a magnetometer. The instrument records magnetic readings, and as the survey grid is completed, software translates the data into a visual map, typically shaded in black and white. Dark or light anomalies may indicate archaeological features such as hearths, kilns, pits, boundary ditches and roads.
It’s important to note that geophysical data alone cannot identify what an anomaly actually is. Interpretation relies on experience, archaeological understanding, and historical context. Until a feature is excavated (and sometimes not even then!), we can only say that an anomaly is present, not definitively what created it.
However, the importance of geophysics in archaeology cannot be overstated. It helps inform decision‑making by allowing archaeologists to identify areas with high archaeological potential, to plan targeted excavation or to avoid unnecessary disturbance altogether.
Case study: A Roman pottery kiln in the New Forest
During routine forest management by Forestry England at a site in the New Forest, large amounts of Roman pottery began appearing. The New Forest is well known as a major Roman pottery production centre. Twelve Roman kilns are already known within 1 km of the site so it was thought that this pottery scatter might represent another production area. To investigate further, our team carried out a magnetic gradiometer survey.
Kilns can show up very strongly on magnetometry surveys because the high temperatures reached during firing modify the magnetic structure of the surrounding soil and the kiln itself. Each time the kiln is fired, the iron particles within the clay and soil become re‑aligned (a.k.a. polarised) in a process known as thermoremanent magnetisation.
The survey revealed strong magnetic anomalies indicating a large area of burning, likely linked to a kiln, while smaller discrete anomalies may represent features associated with pottery production. The patterning of surrounding anomalies even suggests an enclosure defining the limits of this industrial zone.
Without disturbing a single layer, geophysics has outlined what is likely an entire working Roman landscape. With this evidence, we can recognise the high archaeological potential of the area and move toward preserving the site in situ through scheduling and detailed documentation. This site is a powerful reminder of how geophysics allows us not only to uncover the past, but also to safeguard it.
