Erétria, the site of which has been occupied since the third millennium B.C., was in ancient times the most important town on Euboea after Chalkis. In the eighth century B.C., inhabited by Ionian settlers from Attica, it enjoyed a period of great prosperity. When in 500 B.C. the Erétrians, together with the Athenians, gave help to Miletus when
it was threatened by the Persians Darius ordered the town to be destroyed and carried off most of the population to Susa as slaves. It seems, however, to have been rapidly rebuilt. Seven Erétrian vessels took part in the naval battles of Artemision and Salamis, and several hundred hoplites from Erétria fought at Plataiai. In 411 B.C. the Erétrians played a major part in liberating Euboea from Athenian rule by destroying the Athenian vessels which sought refuge in their harbor after a naval battle between Athens and Sparta. Later, in 378 B.C., Erétria joined the Attic maritime league and took part in the fight against Macedon. In 198 B.C. the town was captured by the Romans. Erétria was the birthplace of Menedemos, a pupil of Plato.
The remains of ancient Erétria are the most important on the island. Here and there between the streets of modern houses can be seen the foundations of ancient buildings. The Museum contains finds of Roman material. Northeast of the ancient town is the Theater, built into the plain. Originally it had a stone stage building, with the orchestra on the same level; the seating for the spectators would be on wooden stands. In the fourth century B.C. a stone theater was built, with the orchestra on a lower level, an embanked auditorium and a stone stage building. The dramatic action took place on the orchestra in front of a movable wooden proskenion, which in the early Roman period was replaced by a permanent proskenion of white marble. Southwest of the theater are the remains of a temple of Dionysos and one of the gates in the town walls.
To the east of the theater is the Gymnasion, with a bath-house at its northeast corner.
At the northeast end of the town are the foundations of a temple of Apollo Daphnephoros (the Laurel-Bearer). Sculpture from the pediments (including Theseus carrying off the Amazon Antiope, 520 B.C.) is in the Khalkís Museum.
1km/.75mi northwest of the theater is a tomb with a vaulted roof. The acropolis was surrounded for much of the way by polygonal walls. From a tower on the north side there is a fine view. From the east and west sides of the acropolis walls, traceable for only part of the way, run down towards the shore, where there are other remains of walls.
The marshland in this area, originally an arm of the sea, was drained in antiquity.