426 BC Malian Gulf tsunami

The 426 BC Malian Gulf tsunami devastated the coasts of the Malian and Euboean Gulfs, Greece, in the summer of 426 BC. Thucydides inquired into its causes, and concluded that the tsunami must have been caused by an earthquake. He was thus historically the first known to correctly interpret the cause of a tsunami as a preceding geological event.

Source: Wikipedia — 426 BC Malian Gulf tsunami (CC BY-SA 4.0)