When he was thirty years of age, Cleomenes, King of the Lacedaemonians, surprised Megalopolis by night, forced the guards, broke in, and seized the market-place. Philopoemen came out upon the alarm, and fought with desperate courage, but could not beat the enemy out again; yet he succeeded in effecting the escape of the citizens, who got away while he made head against the pursuers, and amused Cleomenes, till, after losing his horse and receiving several wounds, with much ado he came off himself, being the last man in the retreat. The Megalopolitans escaped to Messene, whither Cleomenes sent to offer them their town and goods again. Philopoemen perceiving them to be only too glad at the news, and eager to return, checked them with a speech, in which he made them sensible, that what Cleomenes called restoring the city was, rather, possessing himself of the citizens; and through their means securing also the city for the future. The mere solitude would, of itself, ere long force him away, since there was no staying to guard empty houses and naked walls.
These reasons withheld the Megalopolitans, but gave Cleomenes a pretext to pillage and destroy a great part of the city, and carry away a great booty.
Awhile after King Antigonus coming down to succour the Achaeans, they marched with their united forces against Cleomenes; who, having seized the avenues, lay advantageously posted on the hills of Sellasia. Antigonus drew up close by him, with a resolution to force him in his strength. Philopoemen, with his citizens, was that day placed among the horse, next to the Illyrian foot, a numerous body of bold fighters who completed the line of battle, forming, together with the Achaeans, the reserve. Their orders were to keep their ground, and not engage till from the other wing, where the king fought in person, they should see a red coat lifted up on the point of a spear. The Achaeans obeyed their order and stood fast, but the Illyrians were led on by their commanders to the attack. Euclides, the brother of Cleomenes, seeing the foot thus severed from the horse, detached the best of his light-armed men, commanding them to wheel about, and charge the unprotected Illyrians in the rear. This charge putting things in confusion, Philopoemen, considering those light-armed men would be easily repelled, went first to the king's officers to make them sensible what the occasion required. But they not minding what he said, but slighting him as a hare-brained fellow (as indeed he was not yet of any repute sufficient to give credit to a proposal of such importance), he charged with his own citizens, at the first encounter disordered, and soon after put the troops to flight with great slaughter. Then, to encourage the king's army further, to bring them all upon the enemy while he was in confusion, he quitted his horse, and fighting with extreme difficulty in his heavy horseman's dress, in rough uneven ground, full of water-courses and hollows, had both his thighs struck through with a thonged javelin. It was thrown with great force, so that the head came out on the other side, and made a severe, though not a mortal, wound. There he stood awhile, as if he had been shackled, unable to move. The fastening which joined the thong to the javelin made it difficult to get it drawn out, nor would any about him venture to do it. But the fight being now at the hottest, and likely to be quickly decided, he was transported with the desire of partaking in it, and struggled and strained so violently, setting one leg forward, the other back, that at last he broke the shaft in two; and thus, got the pieces pulled out. Being in this manner set at liberty, he caught up his sword, and running through the midst of those who were fighting in the first ranks, animated his men, and set them afire with emulation.
Antigonus after the victory asked the Macedonians, to try them, how it happened the horse had charged without orders before the signal?
They answering, that they were against their wills forced to it by a young man of Megalopolis, who had fallen in before his time: "This young man," replied Antigonus, smiling, "did like an experienced commander."This, as was natural, brought Philopoemen into great reputation.
Antigonus was earnest to have him in his service, and offered him very advantageous conditions, both as to command and pay. But Philopoemen, who knew that his nature brooked not to be under another, would not accept them; yet not enduring to live idle, and hearing of wars in Crete for practice' sake he passed over thither. He spent some time among those very warlike, and, at the same time, sober and temperate men, improving much by experience in all sorts of service;and then returned with so much fame that the Achaeans presently chose him commander of the horse. These horsemen at that time had neither experience nor bravery, it being the custom to take any common horses, the first and cheapest they could procure, when they were to march; and on almost all occasions they did not go themselves, but hired others in their places, and stayed at home. Their former commanders winked at this, because, it being an honour among the Achaeans to serve on horseback, these men had great power in the commonwealth, and were able to gratify or molest whom they pleased.