History of the Peloponnesian War

When the preparations were completed on both sides, they closed in battle. Demosthenes occupied the right wing with the Messenians and the few Athenians; while the remainder of the line was formed by the Acarnanians in their several divisions, and the Amphilochian dartmen that were present. The Peloponnesians and Ambraciots were drawn up without distinction, excepting the Mantineans, who kept together more on the left, though not in the extremity of the flank, for the extreme left was held by Eurylochus and his men, opposed to the Messenians and Demosthenes.

When the Peloponnesians, being now engaged, outflanked their opponents, and were surrounding their right, the Acarnanians, rising from the ambuscade, fell on them in the rear, and broke them; so that they did not stand to make any resistance, and, moreover, by their panic threw their main army into flight: for when they saw the division of Eurylochus, and the bravest of their forces being cut to pieces, they were far more alarmed. It was the Messenians, posted in that part of the field with Demosthenes, that performed the chief part of the work.

But the Ambraciots and those in the right wing defeated the division opposed to them, and pursued it back to Argos; for they are the most warlike of all in those parts.