According to various historical sources an earthquake and an associated tsunami wiped out the Greek city of Helike on the Gulf of Corinth in 373 B.C. This study combines stratigraphical data from a new series of sediment cores with archaeological findings of the Helike Project to better assess the fate of Helike. Abrupt lithological changes, for example, from coarse-grained littoral facies at the base to fine-grained lagoonal deposits, in three of the new cores suggest sudden formation of lagoonal or lacustrine conditions in the central delta during tectonic events of subsidence due to fault-slip. These events date before c. 2550 B.C., before 348 cal. B.C.–64 cal. A.D. (probably 373 B.C.), and before 1437–1634 cal. A.D. (probably A.D. 1402). Vertically displaced isochronic surfaces between two neighboring cores may be related to active faulting of the fan-delta north of the Western Helike Fault Zone in 373 B.C. and A.D. 1402. Although the Helike Project reported possible tsunami evidence in earlier cores and trenches, no unequivocal sedimentary traces of a tsunami were identified in the Classical horizons of the new cores.