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

6. The king was in his bath, they say, when the presence of the enemy was announced. At this message he leapt in terror from his tub and dashed out crying that he had been beaten without a battle. [2] And thereafter, as his terror drove him to a succession of fear-struck plans and orders, he sent out two of his friends, one to Pella to cast into the sea the money stored in Phacus,¹ the other to Thessalonica to burn the dockyards. He recalled Asclepiodotus and Hippias and their forces from outpost duty and opened every approach for attack. [3] The king ran off with all the gilded statues at Dium, to prevent their falling into the hands of the enemy, and compelled the inhabitants of that region to move to Pydna. Thereby [p. 109]what might have seemed the rashness of the consul² in advancing to a position from which he could not retire without the consent of the enemy, was turned by the king into well-calculated boldness. [4] For the Romans had two passes by which they could extricate themselves: one through Tempe into Thessaly, the other into Macedonia past Dium. [5] Both of the passes were being held by the king's forces; [6] therefore if the king, by fearlessly holding his own, had resisted the first false appearance of approaching danger, he would have left the Romans no retreat through Tempe to Thessaly, nor any route for bringing up provisions from that direction.³ [7] For even without the opposition of an enemy Tempe is a defile difficult of passage; for besides five miles of narrows through which the road is cramped for a loaded animal, the cliffs on either side are so sheer that one can hardly look down without some dizziness of eye and brain. [8] An additional source of fear is the roar and depth of the Peneüs River flowing through the midst of the canyon. This place, so unfriendly by its very nature, was blocked at four separate points by the king's garrisons. [9] One was at the very entrance near Gonnus, the second at Condylus, an impregnable fort, the third in the vicinity of Lapathus, which they call the Palisade, the fourth set by the road itself where the canyon, in the middle of its course, is at its narrowest. [10] where it can easily be defended by no more than ten soldiers. [11] If the Romans' access to [p. 111]supplies through Tempe, as well as their line of⁴ retreat, had been cut off, they would have had to return to the mountains through which they had descended. [12] As they had deceived the enemy in this by stealth, they could not duplicate the feat without concealment and while the enemy were in possession of the higher summits; and the difficulty they had undergone would have laid low all hope. [13] There was no alternative left in this rash enterprise but to get out into Macedonia past Dium in the teeth of the enemy, and this undertaking, had not the gods deprived the king of his wits, would itself have been of the utmost difficulty. [14] For between the foothills of Mount Olympus and the sea lies an interval of a little more than a mile, half of which space is taken up with the broad estuary of the Baphyrus River, while part of the plain is obstructed by either the temple of Jupiter⁵ or the town. [15] The very small remainder could have been barred off by a ditch of no extravagant size and a palisade, and there was such an abundance of stone and of forest timber at hand that even a wall could have been thrown up and towers erected. [16] Since none of these possibilities revealed themselves to a mind blinded by sudden panic, the king stripped away all his defences and opened every approach to assault [17??] before taking refuge in Pydna.