History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
In this quarter, then, the Lacedaemonians were worsted; but in the rest of the army, and especially in the centre, where King Agis was, and about him the three hundred who were called knights,[*](Chosen from the flower of the Spartan youth and serving as a royal body-guard, on foot as well as on horseback.) they fell upon the older men of the Argives, the so-called five companies, and upon the Cleonaeans, the Orneates, and those of the Athenians that were arrayed with them, and routed them. Most of the enemy did not even wait to come to blows, but when the Lacedaemonians came on gave way at once, some of them being trodden underfoot in their effort to get out of the way before being hemmed in by the Lacedaemonians.
When the army of the Argives and their allies had given way in this quarter, their line was on the point of being broken in both directions; and at the same time the right wing of the Lacedaemonians and the Tegeates was beginning to encircle the Athenians with the outflanking part of their own line; and so danger beset them on both sides, for they were being surrounded in one quarter and had been already defeated in the other.
And they would have suffered more than any part of the whole army if their cavalry had not been present and proved helpful to them. It happened, too, that Agis, perceiving that the left of his own forces, which was opposed to the Mantineans and the thousand Argives, was in distress, gave orders for the whole army to go to the assistance of the part that was in danger of defeat.