Coastal subsidence, destruction layers and earthquakes from an underwater archaeological excavation: Kenchreai, eastern harbour of Roman Corinth, Greece

Abstract

One of the first underwater coastal archaeological excavations was made in the 1960 in Kenchreai (Cenchreae), eastern harbour of Roman Corinth, Greece, near the Isthmus (Corinth) Canal. This excavation brought to light an Isis temple with a destruction layer containing amongst others, packs of more than 100 precious glass panels of opus sectile, testifying to a hitherto unknown mosaic-type wall decorative technique. Above this destruction layer, indicating a violently disrupted renovation of the temple in circa AD 400, thereafter abandoned, an apsidal Christian chapel was constructed, currently also found quasi-submerged. The excavators, inspired by subsidence of piscinae (fishtanks) and theories for earthquake destruction and decline of Roman Corinth, a prosperous town controlling marine routes and commerce between Eastern Mediterranean and Italy, have explained the environmental and occupation history of Kenchreai in terms of three earthquakes with 2.3 m cumulative subsidence. This theory, however, has been challenged on different grounds. New evidence about the glass panels and detailed evaluation of historical, seismological, archaeological and coastal data revealed an about 1 m seismic subsidence of Kenchreai, most of which occurred during a destructive earthquake in circa AD 400, undoubtedly with serious impacts to Corinth. Identification of the causative fault is not easy because of unfavourable lithology and because Kenchreai is in a tectonically complex environment: at the east edges of the uplifting Corinthian coast (marked by a Roman harbour 4 m above water) and of the Isthmus of Corinth, a Plio-Quaternary uplifted horst, inside an active tectonic graben. Kenchreai represents one of the very few cases of seismic coastal subsidence deriving from archaeological data.