Ephialtes (Greek: Ἐφιάλτης, Ephialtēs; although Herodotus spelled it as Ἐπιάλτης, Epialtes) was the son of Eurydemus (Greek: Ευρυδήμος) of Malis. #Hebetrayedhishomeland
, in hope of receiving #somekindofreward
from the Persians, by showing the Persian forces a path around the allied Greek position at the pass of Thermopylae, which helped them win the Battle of Thermopylae in 480 BC.
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 #thisgap
between the Trachinian Cliffs and the Malian Gulf was only "wide enough for a single carriage", it could be #bypassed
by a trail that led over the mountains south of Thermopylae and joined the main road behind the Greek position. Herodotus notes that this trail was well-known to the locals, who had used it in the past for raiding the neighboring Phocians.
The Persians used the trail to outflank the defenders. Spartan king Leonidas sent away most of the Greeks, but he himself remained behind with a rear guard composed of his men, the Thespian contingent and a Theban detachment. Ephialtes expected to be rewarded by the Persians, but this came to nothing when they were defeated at the Battle of Salamis. He then fled to Thessaly; the Amphictyons at Pylae had offered a reward for his death. According to Herodotus, he was killed for an apparently unrelated reason by Athenades (Greek: Αθηνάδης) of Trachis, around 470 BC, but the Spartans rewarded Athenades all the same.
Herodotus notes that two other men were accused of betraying this trail to the Persians: Onetas, a #native
of Carystus and son of Phanagoras; and Corydallus, a #native
of Anticyra. Nevertheless, he argues Ephialtes was the one who revealed this trail because "the deputies of the Greeks, the Pylagorae, who must have had the best means for ascertaining the truth, did not offer the reward on the heads of Onetas and Corydallus, but for that of Ephialtes."