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

27. It was obvious to everyone that he was troubled about the pay and nothing else; but as no one dared to give him the advice he asked for, Antigonus was sent back to announce that the king could use the services of five thousand cavalry only, and would not keep the rest of the host. [2] When the barbarians heard this, there was an indignant outcry from the remainder that they had been to no purpose lured away from their homes. [3] Clondicus again asked whether he would pay what had been agreed upon to these five thousand; and when he saw that to this, too, a devious reply was being concocted, the Gauls returned to the Danube, without injury to the messenger who had tricked them (a fate he had hardly hoped could befall him), but plundering that part of Thrace which adjoined their route. [4] This force of Gauls, even had the king remained inactive at the Elpeüs before the Romans, could if brought into Thessaly through the pass of Perrhaebia have not only stripped the fields by their ravages, so that the Romans could have looked for no provisions from there, but could even have stormed cities as long as Perseus held the Romans [5??] at the Elpeüs, in order to prevent their rescuing the cities of their allies. [6] The Romans would have had to consider their own plight, since they could neither remain if Thessaly, the army's source of supplies, were lost, nor could they advance [p. 179]while the camp of the Macedonians lay before them.¹ [7] By losing this added strength, Perseus weakened to no small degree the morale of the Macedonians, who had been depending on this source of hope.

[8] The same miserliness caused a rift with Gentius. For when Perseus had counted out three hundred talents for the envoys sent by Gentius to Pella, he permitted them to affix their seal to the money; then he sent ten talents to Pantauchus and ordered this paid at once to the king. [9] His own people were transporting the rest of the money marked with the seal of the [10??] Illyrians, and he ordered them to convey it by short stages, and then when the Macedonian frontier was reached, to halt there and wait for messengers from him. [11] After Gentius had received a scant portion of the money, he was continually spurred on by Pantauchus to assail the Romans with an act of hostility, and so he threw into prison Marcus Perpenna and Lucius Petilius, the ambassadors who happened to reach him at this time.² [12] On hearing of this Perseus thought that Gentius had committed himself to fight the Romans in any case, and sent a recall to the one conveying the money, as if his only concern was to save as much booty as possible for the Romans after his own defeat.

Herophon also returned from the court of Eumenes, the secret negotiations being still unrevealed. [13] The Macedonians spread the word that discussion about prisoners had taken place, and Eumenes, to avoid suspicion, informed the consul to this same effect.