Eion (Ancient Greek: Ἠϊών, Ēiṓn), one of two ancient cities named Chrysopolis, was an ancient Greek Eretrian colony in Thracian Macedonia specifically in the region of Edonis. It sat at the mouth of the Strymon River which flows into the Aegean from the interior of Thrace. It is referred to in Thucydides' History of the Peloponnesian War as a place of considerable strategic importance to the Athenians during the Peloponnesian War.
Athenians for the first time attempted to capture Eion in 497 BC during the Ionian Revolt, which was unsuccessful as the revolt ended with Persians re-establishing control over the Thrace, including Eion, and a Persian fortress meant for permanent stay was built there, probably in 492 BC. Eion functioned as one of the main Achaemenid cities in Thrace where food was stored for the Persian king Xerxes I and his great armies. Herodotus and Diodorus speak of Persian garrisons, of which the one at Eion was amongst them, which meant that its senior commander was apparently ethnically Persian. Xerxes had recalled most of the Persian troops from the area in the winter of 480/479 BC. It was then captured by the Delian League in 476 BC under the leadership of the Athenian general Cimon, the son of Miltiades the Younger, who started a siege on the city. Refusing Cimon's offer of an honorable withdrawal, the Persian commander Boges destroyed the treasure, killed his family, and committed suicide as the food ran out. Cimon turned the course of the River Strymon so that it flowed against the city walls, causing the mud brick fortifications to dissolve. The inhabitants were enslaved. The capture of Eion was the beginning of a military campaign undertaken by the newly formed Delian League, whose objective was to clear the Aegean Sea of Persian fleets and pirates in order to facilitate Athenian access to the Hellespont.
