The main source for the events of the battle is Herodotus. According to his account, the Spartans held Thermopylae for three days, and although ultimately defeated, they inflicted serious damage on the Persian army. Most importantly, this delayed the Persians' progress to Athens, providing sufficient time for the city's evacuation to the island of Salamis. Though a tactical defeat, Thermopylae served as a strategic and moral victory, inspiring the Greek forces to defeat the Persians at the Battle of Salamis later the same year and the Battle of Plataea one year later.