The Achaeans at that time were at war with Machanidas, the tyrant of Lacedaemon, who, having a strong army, watched all opportunities of becoming entire master of Peloponnesus. When intelligence came that he was fallen upon the Mantineans, Philopoemen forthwith took the field, and marched towards him. They met near Mantinea, and drew up in sight of the city. Both, besides the whole strength of their several cities, had a good number of mercenaries in pay. When they came to fall on, Machanidas, with his hired soldiers, beat the spearmen and the Tarentines whom Philopoemen had placed in the front. But when he should have charged immediately into the main battle, which stood close and firm, he hotly followed the chase; and instead of attacking the Achaeans, passed on beyond them, while they remained drawn up in their place. With so untoward a beginning the rest of the confederates gave themselves up for lost; but Philopoemen, professing to make it a matter of small consequence, and observing the enemy's oversight, who had thus left an opening in their main body, and exposed their own phalanx, made no sort of motion to oppose them, but let them pursue the chase freely, till they had placed themselves at a great distance from him. Then seeing the Lacedaemonians before him deserted by their horse, with their flanks quite bare, he charged suddenly, and surprised them without a commander, and not so much as expecting an encounter, as, when they saw Machanidas driving the beaten enemy before him, they thought the victory already gained. He overthrew them with great slaughter (they report above four thousand killed in the place), and then faced about against Machanidas, who was returning with his mercenaries from the pursuit. There happened to be a broad deep ditch between them, alongside of which both rode their horses for a while, the one trying to get over and fly, the other to hinder him. It looked less like the contest between two generals than like the last defence of some wild beast brought to bay by the keen huntsman Philopoemen, and forced to fight for his life. The tyrant's horse was mettled and strong; and feeling the bloody spurs in his sides, ventured to take the ditch. He had already so far reached the other side, as to have planted his fore-feet upon it, and was struggling to raise himself with these, when Simmias and Polyaenus, who used to fight by the side of Philopoemen, came up on horseback to his assistance. But Philopoemen, before either of them, himself met Machanidas; and perceiving that the horse with his head high reared covered his master's body, turned his own a little, and holding his javelin by the middle, drove it against the tyrant with all his force, and tumbled him dead into the ditch. Such is the precise posture in which he stands at Delphi in the brazen statue which the Achaeans set up of him, in admiration of his valour in this single combat, and conduct during the whole day.
We are told that at the Nemean games, a little after this victory, Philopoemen being then general the second time, and at leisure on the occasion of the solemnity, first showed the Greeks his army drawn up in full array as if they were to fight, and executed with it all the manoeuvres of a battle with wonderful order, strength, and celerity. After which he went into the theatre, while the musicians were singing for the prize, followed by the young soldiers in their military cloaks and their scarlet frocks under their armour, all in the very height of bodily vigour, and much alike in age, showing a high respect to their general; yet breathing at the same time a noble confidence in themselves, raised by success in many glorious encounters. Just at their coming in, it so happened that the musician Pylades, with a voice well suited to the lofty style of poet, was in the act of commencing the Persians of Timotheus-"Under his conduct Greece was glorious and was free."The whole theatre at once turned to look at Philopoemen, and clapped with delight; their hopes venturing once more to return to their country's former reputation; and their feelings almost rising to the height of their ancient spirit.
It was with the Achaeans as with young horses, which go quietly with their usual riders, but grow unruly and restive under strangers. The soldiers, when any service was in hand, and Philopoemen not at their head, grew dejected and looked about for him; but if he once appeared, came presently to themselves, and recovered their confidence and courage, being sensible that this was the only one of their commanders whom the enemy could not endure to face; but, as appeared in several occasions, were frighted with his very name. Thus we find that Philip, King of Macedon, thinking to terrify the Achaeans into subjection again, if he could rid his hands of Philopoemen, employed some persons privately to assassinate him. But the treachery coming to light, he became infamous, and lost his character through Greece. The Boeotians besieging Megara, and ready to carry the town by storm, upon a groundless rumour that Philopoemen was at hand with succour, ran away, and left their scaling ladders at the wall behind them. Nabis (who was tyrant of Lacedaemon after Machanidas) had surprised Messene at a time when Philopoemen was out of command. He tried to persuade Lysippus, then general of the Achaeans, to succour Messene:
but not prevailing with him, because, he said, the enemy being now within it, the place was irrecoverably lost, he resolved to go himself, without order or commission, followed merely by his own immediate fellow-citizens, who went with him as their general by commission from nature, which had made him fittest to command.
Nabis, hearing of his coming, thought it not convenient to stay; but stealing out of the furthest gate with his men, marched away with all the speed he could, thinking himself a happy man if he could get off with safety. And he did escape but Messene was rescued.