History of the Peloponnesian War

Winter was now drawing towards its close, when the Boeotians took Oropus by treachery, though held by an Athenian garrison. Their accomplices in this were some of the Eretrians and of the Oropians themselves, who were plotting the revolt of Euboea, as the place was exactly opposite Eretria, and while in Athenian hands was necessarily a source of great annoyance to Eretria and the rest of Euboea.