At the Battle of Thermopylae The Spartans were led by Leonidas, and resisted the huge Persian army. After a couple of days, a traitor called Ephialtes led the Persians around the pass behind the Greek army. Realising that defeat was inevitable, Leonidas released many of his men. Those who stayed knew it would be a fight to the death. Leonides kept elite "hoplites" (foot soldiers) who had living sons at home. There were also allied Thespians and Thebans who volunteered to stay.