A geological plastic-relief model to describe the subsoil of Rome

Quaternary geology, through the study of the shallow rock-sediment record, is fundamental to understand the recent dynamics of our planet and its relations with human evolution and the development of civilizations. Quaternary deposits are functional for human settlements, due to their easy digging, and commonly act as foundation soils and as a substrate for anthropogenic soils, which are often of archaeological interest. The city of Rome, with its original settlement sited in the Central Archaeological Area (CAA) and comprising the Palatine Hill, Roman Forum and Colosseum, represents a noteworthy case to study the relations between the geological substrate and the overlaying anthropogenic soils, historical monuments and modern-age buildings. The interest of this area is well demonstrated by numerous geo-archaeological excavations, geognostic drillings, outcrops, and by a complex history of land-use transformation. However, disclosing this large amount of information and disseminating the scientific observations deriving from these data to a wider audience is not particularly easy. Thus, we produced a 3D plastic-relief model of CAA made of polystyrene and stucco at 1:1.000 scale, representing a 1 km2 wide topographic surface with monuments above, and showing the geologic substrate along selected cross sections up to the 100 m depth. The lithostratigraphic subsoil structure is reproduced in detail with well-differentiated: anthropogenic soils, up to 20 m thick; middle Pleistocene-Holocene fluvial formations and pyroclastic units filling paleo-valleys and interfluves; the Pliocene clayey marine bedrock. The 3D reconstruction is useful to visualize the conditioning that external morphology and buried morpho-stratigraphic structure exert on natural risk factors. In fact, it is interesting to observe how amplification effects of seismic waves, flood phenomena and slope instability have influenced and will influence the settlement choices of CAA, the subsequent transformations, and the potential consequences of both seismic risk and future climate extremes in the city of Rome. In addition, the model also offers reconstructions of historical palaeontological excavations near the Colosseum, aimed at teaching geo-palaeontological heritage