When geophysical anomalies are not archaeological: lessons from an urban survey in Terracina, Italy

Non-destructive geophysical surveys have become mainstream in archaeological exploration due to their ability to map the subsurface and pinpoint anomalies that may be related to ancient features. However, in the urban environment, this can become tricky due to, among other things, interference from buried modern infrastructure and poor access to survey spots. The ancient city of Terracina, Italy, located between Naples and Rome was the location of an important ancient Roman port, thought to have been abandoned and silted up between the 15th and 18th centuries. This left larges areas as grassy wasteland or, more recently, covered with asphalt for parking lots. The current study examined one such area using magnetometry, frequency domain electromagnetics and electrical resistivity tomography. Archaeological remains were not seen in aerial photographs from 1911, 1923 and 1943 and a satellite image from 2023, nor reported in previous archaeological studies in the area. Results of the geophysical surveys show a prominent square anomaly, with a clear magnetic and electrically conductive signal located in the center of the field. While it was tempting to interpret the finding as the foundations of an ancient building, examination of an additional aerial photograph from 1956 shows that this is most likely the remains of a sports facility built between 1943 and 1958 and subsequently demolished. Since it does not appear on any readily available municipal map, this study serves as a stark reminder that all available sources of information must be considered and thoroughly examined in such complex settings.