Geoarchaeological evaluation of the Roman topography and accessibility by sea of ancient Osor (Cres Island, Croatia)

We combine geoarchaeological investigations with high-resolution airborne laser scanning (ALS) topographic and airborne laser bathymetric (ALB) measurements to reassess the topography of the Roman city of Apsorus (modern Osor, northeastern Adriatic Sea, Croatia), which has generally been interpreted as important nodal point of Roman maritime traffic. Apsorus is located at the isthmus connecting Cres and Lošinj islands, which is 90 m wide at the narrowest part and dissected by a canal of supposed Roman age. A conspicuous low-lying wetland north of the city has been suggested to be a former sea passage and harbour area. Geoarchaeological coring, sedimentological analysis and radiocarbon dating suggest that this depression was already silted up with terrestrial sediments some 6,000 years ago and, especially in combination with the lower sea-level at that time, could not have been a Roman harbour. The combination of the ALS/ALB topographic data with lower sea-levels reconstructed for the Roman period challenges the traditional view which places ancient Osor on a small island and allows for new interpretations of the accessibility of Osor by sea.