History of the Peloponnesian War

The peace, which after the winning of Euboea was concluded for thirty years, lasted fourteen years. But in the fifteenth year, being the forty-eighth of the priesthood of Chrysis in Argos, Aenesias being then ephor at Sparta and Pythadorus, archon of Athens, having then two months of his government to come, in the sixth month after the battle at Potidaea and in the beginning of the spring, three hundred and odd Thebans led by Pythangelus the son of Phyleides and Diemporus the son of Onetoridas, Boeotian rulers, about the first watch of the night entered with their arms into Plataea, a city of Boeotia and confederate of the Athenians.

They were brought in and the gates opened unto them by Naucleides and his accomplices, men of Plataea that for their own private ambition intended both the destruction of such citizens as were their enemies and the putting of the whole city under the subjection of the Thebans.

This they negotiated with one Eurymachus the son of Leontiadas, one of the most potent men of Thebes. For the Thebans, foreseeing the war, desired to preoccupy Plataea, which was always at variance with them, whilst there was yet peace and the war not openly on foot. By which means they more easily entered undiscovered, there being no order taken before for a watch.

And making a stand in their arms in the market place, they did not, as they that gave them entrance would have had them, fall presently to the business and enter the houses of their adversaries, but resolved rather to make favourable proclamation and to induce the city to composition and friendship. And the herald proclaimed, that if any man, according to the ancient custom of all the Boeotians, would enter into the same league of war with them, he should come and bring his arms to theirs, supposing the city by this means would easily be drawn to their side.