The sedimentary record of the Alkinoos Harbour of ancient Corcyra (Corfu Island, Greece) - geoarchaeological evidence for rapid coastal changes induced by co-seismic uplift, tsunami inundation and human interventions

Ancient Corcyra (modern Kerkyra or Corfu) was an important harbour city and commercial centre since the Archaic period, also due to its geostrategic position on the trade routes between Greece and Italy or Sicily. Corcyra kept its status as one of the prevailing naval powers in the Mediterranean by means of a large naval fleet, needing appropriated harbour basins to be stored and repaired. At least two harbours are documented by historical records and associated archaeological remains, namely the Alkinoos and the Hyllaikos Harbours, both located on either side of a narrow isthmus to the north of the Analipsis Peninsula, where the ancient polis developed. Today, the ancient harbour basins are silted and overbuilt by modern urban infrastructure, concealing their overall extent and topography. The present study aims to reconstruct the complex palaeogeographies of the ancient Alkinoos harbour of Corcyra based on a multi-methodological palaeoenvironmental and geoarchaeological approach. The methods used include sedimentary, geochemical, microfaunal and geophysical investigations that were complemented by archaeological data and results from previous geoarchaeological research. Spatially, the study focusses on the area of the so-called Desylla site west of known Alkinoos Harbour sediments in the midst of the modern city of Corfu. These results were complemented by findings from two geomorphological key sites as well as archaeoseismological traces from the western part of the Analipsis Peninsula. At the Desylla site, we found sedimentary evidence of an Archaic pre-harbour, partly open to the Gulf of Corfu, which was the predecessor of a protected Classical harbour basin. This basin, in use between at least the 4th to 3rd cent. BC and the 1st cent. AD, was delimited to the west by a wall. It represents the central part of the Classical Alkinoos Harbour which was sedimentologically traced, for the first time, from the Desylla site in the west to the Kokotou site in the east, where monumental shipsheds were unearthed during earlier archaeological excavations. Probably, the harbour zone extended even further to the east, where contemporaneous harbour deposits were found associated with the prominent quay wall at the Pierri and Anion sites. Our results show, that, apart from man-made interventions, Corcyra's palaeogeographical evolution is strongly linked to multiple impacts of extreme wave events in the form of tsunami inundation. At least four events (I-IV) are recorded in the natural geoarchives of the Analipsis Peninsula and its surroundings as well as the northern harbour zone of ancient Corcyra. In particular, these events happened between 5600 and 5200 cal BC (event I), after 3900 cal BC (event II), between the 4th and 3rd cent. BC (event III) and between the 3rd and 6th cent. AD, most likely at 365 AD (event IV). Ages of all events correlate well with ages of tsunami traces found on Sicily, the Greek mainland and other Ionian Islands. Tsunami events I and II led to massive environmental changes around the Analipsis Peninsula, while event III was associated to strong co-seismic uplift, leading to the abandonment of the harbour site at Pierri. Decreasing water depths by siltation of the Kokotou and Desylla sites, however, were redressed by dredging, giving rise to an extensive Roman re-use of the western part of the Alkinoos Harbour zone. Yet, both harbour sites were hit again by event IV filling the harbour basins by a thick sequence of event deposits.