History of the Peloponnesian War

Now Brasidas son of Tellis, the Lacedaemonian, happened at this time to be in the neighbourhood of Sicyon and Corinth, preparing an army for Thrace. And when he heard of the capture of the walls, fearing both for the Peloponnesians in Nisaea, and lest Megara should be taken, he sent to the Boeotians with orders to meet him with a body of troops as quickly as possible at Tripodiscus, (it is a village in the Megarean territory that has this name, under Mount Gerania,) and went himself with two thousand seven hundred Corinthian heavy-armed, four hundred Phliasian, six hundred Sicyonian, and all his own forces that had been already raised, thinking that he should still find Nisaea untaken.

But when he heard of its capture, (for he happened to have gone out to Tripodiscus by night,) picking out three hundred men from his army, before he was heard of, he advanced to Megara unobserved by the Athenians, who were about the shore; wishing nominally, and really too, if he could, to make an attempt on Nisaea; but, above all, to effect an entrance into Megara, and secure it. Accordingly he begged them to receive his forces, telling them that he was in hope of recovering Nisaea.