LXX. After this they joined battle, the Argives and their allies advancing with haste and fury, the Lacedaemonians slowly and to the music of many flute-players--a standing institution in their army, that has nothing to do with religion, but is meant to make them advance evenly, stepping in time, without breaking their order, as large armies are apt to do in the moment of engaging.
LXXI. Just before the battle joined, King Agis resolved upon the following manoeuvre. All armies are alike in this: on going into action they get forced out rather on their right wing, and one and the other overlap with this their adversary's left; because fear makes each man do his best to shelter his unarmed side with the shield of the man next him on the right, thinking that the closer the shields are locked together the better will he be protected. The man primarily responsible for this is the first upon the right wing, who is always striving to withdraw from the enemy his unarmed side; and the same apprehension makes the rest follow him.  On the present occasion the Mantineans reached with their wing far beyond the Sciritae, and the Lacedaemonians and Tegeans still farther beyond the Athenians, as their army was the largest.  Agis afraid of his left being surrounded, and thinking that the Mantineans outflanked it too far, ordered the Sciritae and Brasideans to move out from their place in the ranks and make the line even with the Mantineans, and told the Polemarchs Hipponoidas and Aristocles to fill up the gap thus formed, by throwing themselves into it with two companies taken from the right wing; thinking that his right would still be strong enough and to spare, and that the line fronting the Mantineans would gain in solidity.
LXXII. However, as he gave these orders in the moment of the onset, and at short notice, it so happened that Aristocles and Hipponoidas would not move over, for which offence they were afterwards banished from Sparta, as having been guilty of cowardice; and the enemy meanwhile closed before the Sciritae (whom Agis on seeing that the two companies did not move over ordered to return to their place) had time to fill up the breach in question.  Now it was, however, that the Lacedaemonians, utterly worsted in respect of skill, showed themselves as superior in point of courage.  As soon as they came to close quarters with the enemy, the Mantinean right broke their Sciritae and Brasideans, and bursting in with their allies and the thousand picked Argives into the unclosed breach in their line cut up and surrounded the Lacedaemonians, and drove them in full rout to the wagons, slaying some of the older men on guard there.  But the Lacedaemonians, worsted in this part of the field, with the rest of their army, and especially the centre, where the three hundred knights, as they are called, fought round King Agis, fell on the older men of the Argives and the five companies so named, and on the Cleonaeans, the Orneans, and the Athenians next them, and instantly routed them; the greater number not even waiting to strike a blow, but giving way the moment that they came on, some even being trodden under foot, in their fear of being overtaken by their assailants.
LXXIII. The army of the Argives and their allies having given way in this quarter was now completely cut in two, and the Lacedaemonian and Tegean right simultaneously closing round the Athenians with the troops that outflanked them, these last found themselves placed between two fires, being surrounded on one side and already defeated on the other. Indeed they would have suffered more severely than any other part of the army, but for the services of the cavalry which they had with them.  Agis also on perceiving the distress of his left opposed to the Mantineans and the thousand Argives, ordered all the army to advance to the support of the defeated wing;  and while this took place, as the enemy moved past and slanted away from them, the Athenians escaped at their leisure, and with them the beaten Argive division. Meanwhile the Mantineans and their allies and the picked body of the Argives ceased to press the enemy, and seeing their friends defeated and the Lacedaemonians in full advance upon them, took to flight.  Many of the Mantineans perished; but the bulk of the picked body of the Argives made good their escape. The flight and retreat, however, were neither hurried nor long; the Lacedaemonians fighting long and stubbornly until the rout of their enemy, but that once effected, pursuing for a short time and not far.
LXXIV. Such was the battle, as nearly as possible as I have described it; the greatest that had occurred for a very long while among the Hellenes, and joined by the most considerable states.  The Lacedaemonians took up a position in front of the enemy's dead, and immediately set up a trophy and stripped the slain; they took up their own dead and carried them back to Tegea, where they buried them, and restored those of the enemy under truce.  The Argives, Orneans, and Cleonaeans had seven hundred killed; the Mantineans two hundred, and the Athenians and Aeginetans also two hundred, with both their generals. On the side of the Lacedaemonians, the allies did not suffer any loss worth speaking of: as to the Lacedaemonians themselves it was difficult to learn the truth; it is said, however, that there were slain about three hundred of them.
Battle of Mantinea Stage 1 & 2, Battle of Mantinea Stage 3