Geomorphological hazard and cultural heritage: a case-study of the Roman bridges in the Finalese karstic area (Western Liguria - Italy)

This study presents the geological and geomorphological surveys that relate to hazards in the Ponci Valley, which is located in Finale Ligure, Italy. These surveys are considered in light of the important archaeological site from the Roman era that is also located in the Ponci Valley, in order to define its state of vulnerability. This site contains the remains of Via Iulia Augusta, the alternative to the Via Aurelia, built along this valley 2000 years ago. Five bridges cross this road, which are between 150 m and 300 m in altitude. These constitute the most important and monumental traces of the Roman communication routes in Liguria. The bridges are all single arched, with three of them perfectly preserved, and only some vestiges of the abutments and ramps visible for the other two. Since the Pietra di Finale is largely found in this area, this rock is mainly used for building these bridges, supplemented by dolomitic limestone, quartzites, and other schists. The area, which is mainly composed of bioclastic limestone and secondarily of dolomite limestone, is part of the extensive Finalese karstic area. The lithological features, geomorphological evolution, and morpho-structural relationships between the outcropping lithotypes caused the formation of karstic landforms and hypogeal phenomena through rainfall infiltration and underground water flow. Its geomorphological features are characterised by a series of plateau and ridge zones with a number of peaks at limited altitudes, representing rocky towers isolated by deep canyons. This area includes several karstic springs and is crossed by a few water flows, some of which are underground. In addition, flood plains, karstic depressions, swallow-holes and caves are found here. This study highlights the geological, environmental, and cultural value of this site, which is acknowledged as a “geosite” of Mediterranean importance, with respect to geomorphological risk scenarios. Firm hazard reduction measures are needed, in particular related to flash floods, rockslides, and sinkhole events that could affect the Roman bridge remains.