Geophysical prospecting for the pre- and early-historical reconstruction of the subsurface underneath the Paleochristian Basilica of Santa Maria di Compulteria (northern Campania, Italy)

•New 3D-ERT electrode layout investigates the subsurface of a Paleochristian Basilica.•High-resolution ERT and GPR surveys images buried anthropic traces.•Combined geophysical and archaeological data reveals site prehistoric occupation. The medieval Basilica of Santa Maria in Compulteria was built at an important road junction in the Alife Plain (Campania region), a wide basin within the Apennine mountains of southern Italy. Archaeological excavations carried out during the 1990s at shallow depths under the floor of the Basilica discovered the remains of Roman Age buildings, but little is known about their extent and the older phases of occupation of this key site. We present here the results of two high-resolution 3D geophysical surveys – ground penetrating radar and electrical resistivity tomography – carried out to understand the nature and the extent of the structures buried down to about 10 m depth under the modern floor of the Basilica. The geophysical investigations allowed us to find evidence for older anthropogenic traces at a greater depth, which have never been hypothesized. An integrated interpretation of the geophysical measurements with previous archaeological data for the shallow part, and with admissible human traces at depth, has provided an exhaustive reconstruction of the subsurface remains from the upper to the deeper portion of the investigated volume. In particular, our findings highlight anomalous features of likely anthropogenic origin, which are ascribed to historical and pre-historical phases preceding the construction of the middle age Basilica.