Eion (Greek: Ἠϊών, Ēiṓn), ancient 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.