Greece in the 5th century BC BC, the Greeks, under the Spartan Pausanias, defeated the Persian army at Plataea. The Athenian fleet then turned to chasing the Persians out of the Aegean Sea, defeating their fleet decisively in the Battle of Cape Mycale, and in 478 BC the Athenian fleet captured Byzantium. In the course of doing so Athens enrolled all the island states and some mainland allies into an alliance, called the Delian League because the League's treasury was kept on the sacred island of Delos. The Spartans, although they had taken part in the war, withdrew from any further involvement, allowing Athens to become
Battle of Thermopylae by Leonidas (Herodotus admits that there is some doubt about which actually happened). The contingent of 700 Thespians, led by their general Demophilus, refused to leave and committed themselves to the fight. Also present were the 400 Thebans and probably the helots who had accompanied the Spartans. Leonidas' actions have been the subject of much discussion. It is commonly stated that the Spartans were obeying the laws of Sparta by not retreating, but it seems it was actually the failure to retreat from Thermopylae that gave rise to the notion that Spartans never retreated. It is also possible that, recalling