History of the Peloponnesian War

The Corinthians, having long before from Argos had intelligence that an army of the Athenians was coming against them, came all of them with their forces to the isthmus, save only such as dwelt without the isthmus and five hundred garrison soldiers absent in Ambracia and Leucadia; all the rest of military age came forth to attend the Athenians where they should put in.

But when the Athenians had put to shore in the night unseen and that advertisement thereof was given them by signs put up into the air, they left the one half of their forces in Cenchreia lest the Athenians should go against Crommyon: and with the other half made haste to meet them.