“The summit of Olympus, at the site 
Where stands Apollo’s temple, has a height 
Of full ten furlongs by the line, and more, 
Ten furlongs, and one hundred feet, less four. 
Eumelus’s son, Xenagoras, reached the place. 
Adieu, O king, and do thy pilgrim grace.” 

It is allowed, say the geometricians, that no mountain in height or sea in depth exceeds ten furlongs, and yet it seems probable that Xenagoras did not take his admeasurement carelessly, but according to the rules of art, and with instruments for the purpose. Here it was that Nasica passed the night. 
A Cretan deserted, who fled to the enemy during the march, discovered to Perseus the design which the Romans had to encompass him: for he, seeingthat Aemilius lay still, had not suspected any such attempt. He was startled at the news, yet did not put his army in motion, but sent ten thousandmercenary soldiers, and two thousand Macedonians, under command of Milo, with order to hasten and possess themselves of the passes. Polybius relatesthat the Romans found these men asleep when they attacked them; but Nasica says there was a sharp and severe conflict on the top of the mountain, that he himself encountered a mercenary Thracian, pierced him through with his javelin, and slew him; and that the enemy being forced to retreat, Milo stripped to his coat and fled shamefully without his armour, while he followed without danger, and conveyed the whole army down into the country. 
After this event, Perseus, now grown fearful, and fallen from his hopes, removed his camp in all haste; he was under the necessity either to stop before Pydna, and there run the hazard of a battle, or disperse his army into cities, and there expect the event of the war, which, having once made its way into his country, could not be driven out without great slaughter and bloodshed. But Perseus, being told by his friends that he was much superior in number, and that men fighting in the defence of their wives and children must needs feel all the more courage, especially when all was done in the sight of their king, who himself was engaged in equal danger, was thus again encouraged; and, pitching his camp, prepared himself to fight, viewed the country, and gave out the commands, as if he designed to set upon the Romans as soon as they approached. The place was a field fit for the action of a phalanx, which requires smooth standing and even ground, and also had divers little hills, one joining another, fit for the motions whether in retreat or advance of light troops and skirmishers. Through the middle ran the rivers Aeson and Leucus, which though not very deep, it being the latter end of summer, yet were likely enough to give the Romans some trouble. 
As soon as Aemilius had rejoined Nasica, he advanced in battle array against the enemy; but when he found how they were drawn up, and the number of their forces, he regarded them with admiration and surprise, and halted, considering within himself. The young commanders, eager to fight, riding along by his side, pressed him not to delay, and most of all Nasica, flushed with his late success on Olympus. To whom Aemilius answered with a smile: “So would I do were I of your age; but many victories have taught me the ways in which men are defeated, and forbid me to engage soldiers weary with a long march against an army drawn up and prepared for battle.” 
Then he gave command that the front of his army, and such as were in sight of the enemy, should form as if ready to engage, and those in the rear should cast up the trenches and fortify the camp; so that the hindmost in succession wheeling off by degrees and withdrawing, their whole order was insensibly broken up, and the army encamped without noise or trouble. 

When it was night, and, supper being over, all were turning to sleep and rest, on a sudden the moon, which was then at full and high in the heavens, grew dark, and by degrees losing her light, passed through various colours, and at length was totally eclipsed. The Romans, according to their custom, clattering brass pans and lifting up fire-brands and torches into the air, invoked the return of her light; the Macedonians behaved far otherwise: terror and amazement seized their whole army, and a rumour crept by degrees into their camp that this eclipse portended even that of their king. Aemilius was no novice in these things, nor was ignorant of the nature of the seeming irregularities of eclipses- that in a certain revolution of time, the moon in her course enters the shadow of the earth and is there obscured, till, passing the region of darkness, she is again enlightened by the sun. Yet being a devout man, a religious observer of sacrifices and the art of divination, as soon as he perceived the moon beginning to regain her former lustre, he offered up to her eleven heifers. At the break of day he sacrificed as many as twenty in succession to Hercules, without any token that his offering was accepted; but at the one-and-twentieth, the signs promised victory to defenders. He then vowed a hecatomb and solemn sports to Hercules, and commanded his captains to make ready for battle, staying only till the sun should decline and come round to the west, lest, being in their faces in the morning, it should dazzle the eyes of his soldiers. Thus he whiled away the time in his tent, which was open towards the plain where his enemies were encamped. 
Aemilius Paulus by Plutarch