At which battle did Sparta defeat Argos in 494 BCE?

Sparta defeated Argos at the Battle of Sepeia in about 494 BCE.

The battle was fought near Tiryns in the territory of Argos during the reign of the Spartan king Cleomenes I. According to Herodotus, Cleomenes used a signal associated with mealtime to exploit the Argive army’s expectations. Spartan troops attacked when the Argives were less prepared, contributing to a major Spartan victory.

Ancient accounts give the battle a very large death toll for the Argive side, though the exact figures and details are debated by modern historians. The defeat weakened Argos and strengthened Sparta’s influence in the northeastern Peloponnese.

Sepeia is sometimes confused with the Battle of Hysiae, another earlier conflict between Argos and Sparta. Hysiae occurred in the sixth century BCE, while Sepeia belongs to the late sixth or early fifth century BCE and is particularly associated with Cleomenes I.