Legacy imagery, continuous satellite monitoring and targeted drone surveys for the study of deserted medieval fortified settlements in the hinterland of Ravenna, Italy

The nucleation of the rural population was a widespread phenomenon during the Middle Ages that interested many areas of Western Europe. However, many of these sites are now deserted with the underlying phenomena causing these abandonments not always easy to reconstruct. Archaeologists have been interested in these medieval settlements since the middle of the 19th century, and remote sensing has played a decisive role in mapping hundreds of them. This also applies to many parts of the Po Valley but not the Romagna plain, where hundreds of medieval sites are known but almost exclusively based on written sources. However, the increasing availability of aerial and satellite images offers a valuable opportunity to bridge this knowledge gap. The systematic study of legacy images allowed the mapping of new defensive elements and reconstruction of the general plan of six deserted medieval fortified settlements in the broader hinterland of Ravenna. PlanetScope 3m resolution images were later exploited to continuously monitor these sites during periods prone to crop marks formation to detect the presence of wide crop/soil marks (e.g. ditches). Six successful field verifications demonstrate that these ‘coarse’ images are sufficient to plan drone surveys that can allow the mapping of additional smaller features.