Born to Eurydemus (Εὐρύδημος) of Malis,[1] he betrayed his homeland and people to the Achaemenid Empire by revealing the existence of a path around the Greek coalition's position at Thermopylae.
[2] His efforts allowed the Persian army to overrun the Greeks' defensive formation and thereby win the Battle of Thermopylae in September 480 BCE.
[citation needed] The allied Greek land forces, which Herodotus states numbered no more than 4,200 men, had chosen Thermopylae to block the advance of the much larger Persian army.
Although this gap between the Trachinian Cliffs and the Malian Gulf was only "wide enough for a single carriage",[3] it could be bypassed by a trail that led over the mountains south of Thermopylae and joined the main road behind the Greek position.
"[6] In the 1962 film The 300 Spartans, Ephialtes was portrayed by Kieron Moore and is depicted as a shady farmhand who worked on a goat farm near Thermopylae.