The geological record of ancient harbours : using ancient harbour geoarchives of Corcyra (Greece) to reconstruct the palaeoenvironmental development and to identify extreme events by means of a multi-proxy based geoarchaeological approach
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Abstract
Ancient harbours represent valuable geoarchives where complex man-environment interactions are recorded. Thus, various ancient harbours were studied in the frame of geomorphological and geoarchaeological research in order to gain new insights into the (palaeo-)history of the Mediterranean region.
The ancient city of Corcyra, located on the island of Corfu in the northern Ionian Sea, has not been subject to geoarchaeological research so far, although Corcyra was one of the major commercial and political centres in the ancient Greek world. At least two ancient harbours are known from historical records and traced by archaeological remains of related infrastructure, namely the Alkinoos Harbour and commercial Hyllaikos Harbour, located to the west and the north of the ancient city, respectively. However, information on the exact extent of these harbours as well as their temporal and spatial development are incomplete as much of the ancient infrastructure is concealed under modern urban structures nowadays.
The present study focusses the harbour geoarchives of Corcyra in order to decipher the complex and multifaceted palaeogeographical history of ancient Corcyra. In particular, the study aims to (i) trace the spatial extent of the ancient harbour basins, (ii) investigate the sedimentary record of these harbours in order to draw conclusions on their environmental conditions and protection levels, (iii) identify the main triggers for palaeoenvironmental changes in these harbours and their natural predecessors/successors and (iv) study the harbour’s function as sediment traps for human interventions and natural extreme events. Six investigation sites were analysed by means of a comprehensive geoarchaeological multi-methodological approach including sedimentological, geomorphological, palaeontological, geochemical and geophysical investigations which were complemented by results from archaeological research. These study sites comprised three potential harbour sites, namely the Desylla, Kokotou and Pierri sites, which were identified based on historical accounts or archaeological remains, as well as three geomorphological key sites.
First rudimentary harbour installations in Corcyra trace back to the Archaic period, when a slightly-protected pre-harbour came to function by the construction of a nearby wall at the Desylla site in the northern ancient city. Out of this still shallow marine environment, the Classical Alkinoos Harbour developed before the 4th to 3rd cent. BC, extending to the east towards the Kokotou site, where the archaeological remains of monumental shipsheds bear witness of extensive harbour use. Probably, the harbour basin extended even further to the east as a contemporaneous harbour basin was reconstructed in the front of the Pierri quay wall. During Roman times, only the western part of the northern harbour zone was used and kept in function by extensive dredging activities proved by stratigraphical gaps, chronological anomalies and geophysical evidence. In contrast, the Pierri site quay wall was buried under colluvial and anthropogenic deposits.
Apart from these man-made interventions that led to massive coastal change on the shores of the Analipsis Peninsula, where the ancient city was located, the coastal evolution of Corcyra was also strongly linked to natural extreme events. Evidence of multiple palaeotsunami landfalls was found in the investigated areas, documenting tsunami impact in the 6th mill. BC, the 4th mill. BC, between the 4th and 3rd cent. BC, between the 3rd and 6th cent. AD and between the 5th and 6th cent. AD. Most of these events seem to correlate with findings from Sicily, the Albanian coasts, the Greek mainland and other Ionian Islands and are therefore considered to be part of supra-regional impacts. Only the tsunami event that happened between the 4th and 3rd cent. BC was identified as local event triggered around Corfu, as associated strong co-seismic uplift was proved at the Pierri quay wall and by archaeoseismological traces on the Analipsis Peninsula. Due to decreased water depth caused by this crustal uplift and associated infill of tsunami event deposits, the Pierri was not navigable anymore and abandoned. Similarly, the decline of the Roman Alkinoos Harbour was initialised by event deposits which were most likely caused by the 365 AD Crete tsunami.
By conclusion, the ancient harbours of Corcyra turned out to be appropriate geoarchives to reconstruct the palaeoenvironmental history of Corcyra and to trace multiple interactions between men and the natural environment.