Titus Livius (Livy), The History of Rome, Book 31
Cyrus Evans, Ed.

39. The consul was now taking refreshment, when he was told that the herald had arrived, and on what business; [2] he gave him no other answer, than that he should be admitted to an audience early the next morning: by which means Philip gained what he wanted —the length of that night, and part of the following day, during which he might get the start on his march. [3] He directed his route towards the mountains, a road which he knew the Romans with their heavy baggage would not attempt. The consul, having, at the first light, dismissed the herald with a grant of a truce, in a short time after discovered that the enemy had gone off; but not knowing what course to take in pursuit of them, he remained in the same camp for several days, which he employed in collecting forage. [4] He then marched to Stubera, and brought thither, from Pelagonia, the corn that was in the fields. From thence he advanced to Pluvina, not having yet discovered to what quarter the Macedonian had bent his course. [5] Philip, having at first fixed his camp at Bryanium, marched thence through cross-roads, and gave a sudden alarm to the enemy. The Romans, on this, removed from Pluvina, and pitched their camp near the river Osphagus. [6] The king also sat down at a small distance, forming his intrenchment on the bank of a river which the inhabitants call Erigonus. [7] Having there received certain information that the Romans intended to proceed to Eordaea, he marched away before them, in order to take possession of the defiles, and prevent the enemy from making their way, where the roads are confined in narrow straits. [8] There, with great haste, he fortified some places with a rampart, others with a trench, others with stones heaped up instead of walls, others with trees laid across, according as the situation required, or as materials lay convenient; [9] and thus a road, in its own nature difficult, he rendered, as he imagined, impregnable by the works which he drew across every pass. [10] The adjoining ground, being mostly covered with woods, was exceedingly incommodious to the phalanx of [p. 1382]the Macedonians, which is of no manner of use, except when they extend their very long spears before their shields, forming as it were a palisade; to perform which, they require an open plain. [11] The Thracians, too, were embarrassed by their lances, which also are of a great length, and were entangled among the branches that stood in their way on every side. [12] The body of Cretans alone was not unserviceable; and yet even these, though, in case of an attack made on them, they could to good purpose discharge their arrows against the horses or riders, where they were open to a wound, yet against the Roman shields they could do nothing, because they had neither strength sufficient to pierce through them, nor was there any part exposed at which they could aim. [13] Perceiving, therefore, that kind of weapon to be useless, they annoyed the enemy with stones, which lay in plenty in all parts of the valley: the strokes made by these on their shields, with greater noise than injury, for a short time retarded the advance of the Romans; [14] but quickly disregarding these missiles also, some, closing their shields in form of a tortoise, forced their way through the enemy in front; [15] others having, by a short circuit, gained the summit of the hill, dislodged the dismayed Macedonians from their guards and posts, and even slew the greater part of them, their retreat being embarrassed by the difficulties of the ground.