Argos, which has fought intermittently with Sparta and often allied itself with Athens, is attacked in 494 by Cleomenes I of Sparta, who surprises the Argive soldiers during their supper and defeats them at the Battle of Sepeia near Tiryns, fully establishing Spartan dominance in the Peloponnese.

The closet thing to a contemporaneous source for the description of the battle is, as for many events in this time period, the Histories of Herodotus (written approximately fifty years later, circa 440 BCE).

According to Herodotus, the Spartan army tricked the Argives into believing that the Spartans were going to their evening meal, and when the Argives did the same, the Spartans seized up their arms and attacked them, gaining an overwhelming victory.

The battle is a controversial one in terms of the Spartan legend for, according to Herodotus, Cleomenes massacred the remaining Argives—most by burning them alive in the sacred grove of Argos to which they had fled for refuge.