History of the Peloponnesian War

At this time Brasidas son of Tellis, a Lacedaemonian, happened to be in the neighbourhood of Sicyon and Corinth, preparing a force for use in the region of Thrace. And when he heard of the capture of the walls, fearing for the safety of the Peloponnesians in Nisaea and apprehensive lest Megara should be taken, he sent to the Boeotians requesting them to come in haste with an army and to meet him at Tripodiscus, which is the name of a village in the district of Megara at the foot of Mount Geraneia. He himself set out with two thousand seven hundred Corinthian hoplites, four hundred from Phlius, seven hundred from Sicyon, and such troops of his own as had already been levied, thinking that he would arrive before Nisaea had been taken.

But when he learned the truth—for he happened to have gone out by night to Tripodiscus—he selected three hundred of his own army, and before his approach was known reached the city of Megara unobserved by the Athenians, who were down by the sea. His plan was, ostensibly—and really, too, if it should prove possible—to make an attempt upon Nisaea, but most of all to get into the city of Megara and secure it. And he demanded that they should receive him, saying that he was in hopes of recovering Nisaea.