Titus Livius (Livy), The History of Rome, Book 44
Alfred C. Schlesinger, Ph.D., Ed.

8. Greatly pleased by this news, the consul moved from Dium to Phila, both to strengthen its garrison and to distribute to the soldiers the grain, transportation of which was slow. [2] This march started unpleasant rumours; for some put it that he had retired from before the enemy out of fear, because he would have had to fight a battle if he had remained in Pieria, while others said that [3??] in his ignorance of the daily fluctuations in the fortunes of war, and as if events were awaiting his signal, he had dropped from his grasp advantages which presently could not be recovered. [4] For at one move he had lost his grip on Dium and had stirred up the enemy to perceiving at long last that he must recover what previously he had shamefully lost. [5] For on hearing of the departure of the consul, the king returned to Dium, rebuilt what had been cast down and despoiled by the Romans, replaced the battlements knocked off the walls, and strengthened the walls all around. Then he placed his camp five miles from the city on the nearer bank of the Elpeüs River, intending to use the river itself as a fortification since it was very hard to cross. [6] It flows from a ravine of Mount Olympus, is scanty in summer, but again in [p. 117]winter is swollen by rains; it forms great rapids¹ above its boulders, and below, by carrying off the eroded earth to the sea, produces great abysses and banks sheer on either side above a deeply-hollowed channel. [7] Thinking that the enemy's advance was barred by this river, the king intended to use up the rest of the summer.

[8] Meanwhile the consul sent Popilius with two thousand soldiers from Phila to Heracleum. [9] This is about five miles from Phila, on a cliff overhanging the river midway between Dium and Tempe.