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.