Integrated geophysical methods for the characterisation of an archaeological site (Massenzio Basilica - Roman forum, Rome, Italy)

The Massenzio Basilica was built by Emperor Massenzio in the AD 308 until AD 312, it is one of the biggest Monuments of the Roman age after the Coliseum. It spreads in 100x65 square meters and 40 meters high. Now only an aisle remains to evidence the size of the Monument. A general study has been performed in the frame of co-operation between Superintendence of cultural heritage of Rome and University of Rome with the aim to have better knowledge of the Monument both historic artistic as structural point of view. At first bore-hole investigation was performed then to improve and increase the knowledge of the site the study was implemented with a geophysical survey. To characterise the soil where the Monument was built we used electrical resistivity tomography (ERT), vertical electrical survey (VES) and seismic refraction technique, to obtain information about the foundation structures ERT surveys and ground penetrating radar (GPR) were used. The data obtained with the bore-hole investigation were interpolated with the results of 15 VES performed with Schlumberger array having maximum distance between the electrodes AB=100m. The VES were located inside and outside the Basilica (Fig.1). Electric data were inverted by using the steepest descend method (Koefoed 1979). The interpretation of SEV performed inside the Basilica indicated the presence of three layers, characterised respectively from the top to the bottom by a resistivity of about 200ohm.m 2 meters depth, 20ohm.m 16 meters depth and 5ohm.m. The first layer was identified with the concrete floor of the Basilica, the resistivity values of second layer were ascribed to silt clay materials typical of fluvial lacustrine formation and the third layer was identified as clay formation. Resistivity curve of Mas15 with the interpretation is shown in the fig.2. To confirm the results obtained with the VES a multielectrode dipole-dipole array was performed inside the Basilica, (line C).