Ground penetrating radar and electrical resistivity tomography investigations in the southern sector of the Roman Forum: First results on the pre-Augustan phases of the Basilica Julia

A research project aimed at the study of the archaeological context of the BasilicaJulia in the Roman Forum (Rome, Italy) and the transformation phases of the buildinginvolved the use of different techniques of geophysical prospecting. In particular,Ground-penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) surveyswere carried out in order to record the buried structures of the Basilica and the previousbuildings laying in the southern part of the Forum. These geophysical methodshave been chosen in order to guarantee a good compromise between resolution(GPR in the shallow subsurface) and depth of investigation (ERT in the deeper subsurface),with the aim of investigating up to a depth of about 10 m in a very conductivesubsoil. In particular, GPR surveys were conducted in the five aisles of themonument, while ERT measurements were performed with nonstandard acquisitionmode in order to include the entire perimeter of the building. These techniquesallowed us to acquire new data on the structures buried in the sectors of the monumentalcomplex that have never been excavated and on the paleosoil till a depth ofabout 10 m from the surface. Interesting data were acquired on the Basilica Juliaitself, built during the late Republican period (54-46 BC) and rebuilt at the beginningof the first century AD, such as the technical features of the caementicium and travertinefoundations, their relationship with the Cloaca Maxima and the traces of adesign change occurred during the construction in the central aisle of the building;other buried remains of the previous Basilica Sempronia, constructed in 169 BC inthe same area, were identified. Moreover, the investigations documented thepaleosoil in the area between the Forum and the Velabrum to the south, between7.5-8.5 and 5.5 m a.s.l. These data confirmed the general geological setting of thearea, obtained from previous coring, but significantly specified the geomorphology ofthis border sector of the Roman Forum, which slopes down towards the south andthe west.