There is evidence of Greek-speaking peoples populating the islands and coasts of the Aegean Sea as far back as the second millennium BC. Those peoples who migrated eastward and either settled in Attica, or sailed across to the coasts of Asia Minor to found new colonies, became known as the Ionian Greeks.

Although the Ionians maintained close relationships with the inhabitants of Attica, by about 500 BC, all of the colonies in Asia Minor recognized the supremacy of the Persian king's representative, the satrap, based in his city of Sardis. In return for tribute payments these cities were generally left alone to manage their own affairs. However, in the aftermath of the Athenian revolution, several of these cities became involved in a rebellion against Persian rule.

Their revolt lasted for six years before it was finally defeated in 494 BC. The Persians then made an example of several of the Ionian cities by carrying off their inhabitants to Persia to be resettled, sold as slaves, or in the case of many young men, made into eunuchs. Because of the help Athens and other cities had given the Ionians, the revolt provided the Persians with a perfect pretext to invade Greece itself.