Eretria was listed by Homer as one of the Greek cities which sent ships to the Trojan War. In the 8th century BC, Eretria and her near neighbour and rival, Chalcis, were both powerful and prosperous trading cities, and the Eretrians controlled the Aegean islands of Andros, Tenos and Ceos. They also held lands in Boeotia on the Greek mainland.
At the end of the 8th century, however, Eretria and Chalcis fought a prolonged war known (mainly from the account in Thucydides) as the Lelantine War. Little is known of the details of this war, but it is clear that Eretria was defeated. She lost her lands in Boiotia and her Aegean dependencies. Neither Eretria nor Chalcis ever again counted for much in Greek politics.
As a result of this defeat, Eretria turned to colonisation. She planted colonies in the northern Aegean, on the coast of Macedon, and also in Italy and Sicily.
The Eretreans were Ionians, and were thus natural allies of Athens. When the Ionian Greeks in Asia Minor rebelled against Persia in 499, Eretria joined Athens in sending aid to the rebels. As a result, Darius made a point of punishing Eretria during his invasion of Greece. In 490 the city was sacked and burned by the Persians.
During the 5th century the whole of Euboia became part of the Delian League, which later became the Athenian Empire. During the Peloponnesian War Eretria was an Athenian ally against her Dorian rivals Sparta and Corinth. But soon the Eretrians, along with the rest of the Empire, found Athenian domination oppressive. When the Spartans defeated the Athenians at the battle of Eretria in 411, the Euboian cities all rebelled.
After her eventual defeat by Sparta in 404, Athens soon recovered, and re-established her hegemony over Euboia, which was an essential source of grain for the urban population. The Eretrians rebelled again in 349, and this time the Athenians could not recover control. In 343 supporters of Philip II of Macedon gained control of the city, but the Athenians under Demosthenes recaptured it in 341.
The Battle of Chaeronea in 338, in which Philip defeated the combined armies of the Greeks, marked the end of the Greek cities as independent states, and Eretria dwindled to become a provincial town. In 198 it was plundered by the Romans. In 87 it was finally destroyed in the Mithridatic Wars and abandoned.
The modern town of Eretria was established in 1824, after Greek independence, and is now a popular beachside resort. Excavations of ancient Eretria began in the 1890s and have been conducted since 1964 by the Greek Archaeological Service (11th Ephorate of Antiquities) in collaboration with the Swiss School of Archaeology, who also established its archaeological museum. The most important site excavated is the Temple of Apollo Daphnephoros.