The Delian League had been formed between Athens and many of the city-states of the Aegean to continue the war with Persia, which had begun with the first and second Persian invasions of Greece (492–490 and 480–479 BCE, respectively). In the aftermath of the Battles of Plataea and Mycale, which had ended the second invasion, the Greek Allies had taken the offensive, besieging the cities of Sestos and Byzantium. The Delian League then took over responsibility for the war, and continued to attack Persian bases in the Aegean throughout the next decade.