The book on the Macedonian Wars belongs to the less preserved parts, but fortunately, we have access to Appian's sources Polybius or Livy.
The translation was made by Horace White; notes by Jona Lendering.
Outbreak of the Third Macedonian War (Cont'd)
 [From Constantine Porphyrogenitus, The Embassies] When Perseus learned these facts he sent other ambassadors to Rome,note[171 BCE.] who said that the king was surprised and wished to know for what reason they had abandoned the agreement and sent around legates against himself, their ally. If they were offended at anything, they ought to discuss the matter first. The Senate then accused him of the things that Eumenes had told them, and also of what Eumenes had suffered, and especially that Perseus had taken possession of Thrace and had collected an army and war material, which were not the doings of one desiring peace. Again he sent ambassadors who, deeply grieved, spoke as follows in the senate chamber: "To those who are seeking an excuse for war, o Romans, anything will serve for a pretext, but if you have respect for treaties - you who profess so much regard for them - what have you suffered at the hands of Perseus that you should bring war against him? It cannot be because he has an army and war material. He does not hold them against you, nor do you prohibit other kings from having them, nor is it wrong that he should take precautions against those under his rule, and against his neighbors, and foreigners who might have designs against him. But to you, Romans, he sent ambassadors to confirm the peace and only recently renewed the treaty.
 [From Constantine Porphyrogenitus, The Embassies] But, you say, he drove Abrupolis out of his kingdom. Yes, in self-defense, for he had invaded our territory. This fact Perseus himself explained to you, and afterward you renewed the treaty with him, as Eumenes had not yet slandered him. The affair of Abrupolis antedates the treaty and seemed to you just when you ratified it. You say that he made war on the Dolopians, but they were his own subjects. It is hard if he is to be obliged to give an account to you of what he does with his own. He gives it nevertheless, being moved by his high regard for you and for his own reputation. The Dolopians put their governor to death with torture, and Perseus asks what you would have done to any of your subjects who had been guilty of such a crime. But the slayers of Arthetaurus lived on in Macedonia! Yes, by the common law of mankind, the same under which you give asylum to fugitives from other countries. But when Perseus learned that you considered this a crime he forbade them his kingdom entirely.
 [From Constantine Porphyrogenitus, The Embassies] He gave aid to the Byzantines, the Aetolians, and the Boeotians, not against you, but against others. Of these things our ambassadors advised you beforehand, and you did not object until Eumenes uttered his slander against us, which you did not allow our ambassadors to answer in his presence. But you accuse Perseus of the plot against him at Delphi. How many Greeks, how many barbarians, have sent ambassadors to you to complain against Eumenes, to all of whom he is an enemy because so base a man! As for Erennius of Brundusium, who would believe that Perseus would choose a Roman citizen, your friend and patron, to administer poison to the Senate, as though he could destroy the Senate by means of him, or by destroying some of them render the others more favorable to himself ? Erennius has lied to those who are inciting you to war, furnishing them a plausible pretext. Eumenes, moved by hatred, envy, and fear, does not scruple to make it a crime on the part of Perseus that he is liked by so many people, that he is a Philhellene, and that he leads the life of a temperate ruler, free from drunkenness and luxury. And you endure to listen to such stuff from this accuser!
 [From Constantine Porphyrogenitus, The Embassies] Beware lest his slanders multiply against yourselves, if you cannot endure temperate, honest, and industrious neighbors. Perseus challenges Erennius and Eumenes and anybody else to scrutiny and trial before you. He reminds you of his father's zeal and assistance to you against Antiochus the Great. You realized it very well at the time; it would be base to forget it now. He invokes the treaties that you made with his father and with himself, and he does not hesitate to exhort you to fear the gods by whom you swore, and not to bring an unjust war against your allies and not to make nearness, sobriety, and preparation causes of complaint. It is not worthy of you to be stirred by envy and fear like Eumenes. On the contrary, it will be the part of wisdom for you to spare neighbors who are diligent and, as Eumenes says, are well prepared!"
 [From Constantine Porphyrogenitus, The Embassies] When the ambassadors had thus spoken, the Senate gave them no answer, but made a public declaration of war, and the consul ordered the ambassadors to depart from Rome the same day and from Italy within thirty days. The same orders were proclaimed to all Macedonian residents. Consternation mingled with anger followed this action of the Senate, that, on a few hours' notice, so many people were compelled to depart together, who were not able to find animals in so short a time, or to carry all their goods themselves. Some, in their confusion, could not reach a lodging place, but passed the night in the middle of the roads. Others threw themselves on the ground at the city gates with their wives and children. Everything happened that was likely to follow such an unexpected decree, for it was unexpected to them on account of the pending negotiation.