426 BC Malian Gulf tsunami
425 BCE.
Shown on the map at 38.869°, 22.617°.
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. Herodotus, in contrast, had attributed the Potidaea tsunami to the divine wrath of Poseidon.
Text from the Wikipedia article 426 BC Malian Gulf tsunami, licensed CC BY-SA 4.0.