Geoarchaeological investigations of a prominent quay wall in ancient Corcyra - Implications for harbour development, palaeoenvironmental changes and tectonic geomorphology of Corfu Island (Ionian Islands, Greece)

In antiquity, the harbour-city of Corcyra (modern: Corfu) was a prevailing naval power in the Mediterranean and had several harbours to host a considerable fleet. Today, these harbours are totally or partly silted and concealed under modern urban infrastructure. Comprehensive geoarchaeological studies were conducted on the northeastern fringe of the Analipsis Peninsula where excavations have revealed the archaeological remains of a massive quay wall (Pierri and Arion sites). These remains are located east of known ancient harbour structures that belong to the Alkinoos Harbour. Our study aimed to reconstruct the palaeoenvironmental setting of the harbour facilities at the Pierri site, including the analysis of the local sedimentary record in order to detect and differentiate natural and man-made triggers that caused environmental shifts. At the Pierri site, we found geoarchaeological evidence for an ancient harbour basin related to the prominent quay wall. Associated harbour sediments indicate a protected harbour which was developed from an open shallow marine environment, most probably by the construction of breakwaters. Harbour deposits were dated using radiocarbon analyses and diagnostic ceramic fragments to the 4th to 3rd cent. BC. This is in good agreement with the age of the harbour installations as such archaeologically assigned to the Classical and Hellenistic period. The Pierri site was possibly in function as a harbour facility even before the 4th cent. BC. In any case, it was strongly hit by an earthquake and associated tsunami event during Classical to Hellenistic times. By this event, the harbour was uplifted and covered by event deposits so that it was not usable any more. It was subsequently buried by anthropogenic and colluvial sediments. Overall, the Pierri coastal archive allowed to identify three distinct tsunami landfall events, namely before 2483-2400 cal BC (event I), after 2483-2400 cal BC and before 370-214 cal BC (event II), and during Classical to Hellenistic times, most probably between the 4th and 3rd cent. BC (event III). Another tsunami event (event IV) potentially hit the site when it was dry land. Ages of tsunami events I-II and candidate tsunami IV are consistent with tsunamis known from the coasts of western Greece and southern Italy and where thus classified as supra-regional tele-events. Event III was identified as associated to a local earthquake and tsunami by which Corfu Island was uplifted and, at the same time, tilted with a vertical offset of 1.74 m from W to E.