Palaeoenvironmental evolution of the ancient harbor of Lechaion (Corinth Gulf, Greece): Were changes driven by human impacts and gradual coastal processes or catastrophic tsunamis?

The Corinth Gulf, Central Greece, is one of the most rapidly widening tectonic rifts on Earth, where large earthquakes with magnitudes of up ~7.0 have been documented not only by instrumental records but also assessed from historical reports extending back to the 5th century BCE. Several of these earthquakes were associated with tsunamis, particularly in the western part of the Gulf. Of particular interest is the ancient harbor of Lechaion in the eastern side of Corinth Gulf. We reexamine the hypothesis that Lechaion was hit by high-energy tsunami waves in the 8th–6th century BCE, 1st–2nd century CE, and during the 6th century CE. On the basis of sedimentological, seismotectonic, archaeological and historical data, completed with field observations, we support that there is no evidence for tsunami impact in Lechaion. Local stratigraphy and environmental changes are rather interpreted by human impacts and gradual coastal processes. Such interpretations confirm that the tsunami potential in the east Corinth Gulf is relatively low. •No historical or archaeological evidence that tsunami waves inundated Lechaion in the 8th-6th c. BC, 1st-2nd and 6th c. AD.•The tsunami potential in the east Corinth Gulf is at all evidence low as compared to that on the west part of the Gulf.•Ambiguous evidence of tsunami inundation as the mechanism forming the beachrocks in Lechaion.•The role of human intervention versus catastrophic scenarios to explain the historical evolution of ancient Lechaion.•The historical evolution of the Lechaion inner harbour can be divided into three main phases.•Harbour initial formation in the Kypselids period (7th-6th c. BC) - continuous operation until the Roman invasion (146BC).•Destruction by the Romans, desertion and entrance closure that lasted for about 100years.•Harbour reconstruction in the 1st century AD after the Roman colonization of Corinth in 44BC.•Works of this period: foreharbour, retaining walls in the entrance channel and dredging of the inner basins.•The Early Christian Basilica situated on the land barrier between the inner harbour and the coast completed after 530AD.•It was neither destroyed by the AD 521, 524/525 or 551/552 earthquakes nor inundated and buried by tsunami waves.•The Basilica remained in use until at least the mid-7th century AD.•Damage or destruction of it can be linked with the invasion and devastation caused by the Arabs and Slavs ca. 580AD.