Eretria (ĕrē´trēə), ancient city of Greece, in Euboea (now Évvoia), SE of Chalcis (now Khalkís), its rival. In the 7th and 6th cent. BC, Eretria sent out many colonists to islands and coasts of the N Aegean. It supported (499 BC) the Ionian cities in the revolt against Persian control. In retaliation Darius I destroyed (490 BC) the city. Athens planted (c.445 BC) a colony there, which revolted in 411 with the rest of Euboea. Much later, after the second Delian League had been created, Eretria again revolted (349 BC). Excavations have uncovered the city walls, temple of Apollo, theater, and some public buildings.