I have already stated that Cydas the Cretan, who was serving under Eumenes and held in especial honour by him, first of all came to <a class="linkToPlace" target="_blank" href="/place?placename=Amphipolis&groupId=320&placeId=623">Amphipolis</a> and communicated with Cheimarus a Cretan soldier in the service of Perseus, and on a second occasion at <a class="linkToPlace" target="_blank" href="/place?placename=Demetrias&groupId=536&placeId=1006">Demetrias</a> actually came up to the walk, and held converse first with Menecrates and afterwards with Antimachus.
And again that Herophon was twice sent by Perseus on a mission to Eumenes, and that in consequence of this, most of the Romans had a not unfounded suspicion of King Eumenes, is clear from their treatment of Attalus.
For they allowed the latter to come to <a class="linkToPlace" target="_blank" href="/place?placename=Rome&groupId=935&placeId=1669">Rome</a> from <a class="linkToPlace" target="_blank" href="/place?placename=Brundisium&groupId=411&placeId=762">Brundisium</a> and address the senate on any subject he chose, and at last sent him back after replying courteously to him, although he had not given any great assistance either previously or in the war with Perseus;
but as for Eumenes, who had been of the greatest service to them and given them the greatest assistance in their wars against Antiochus and Perseus, they not only prevented him from coming up to <a class="linkToPlace" target="_blank" href="/place?placename=Rome&groupId=935&placeId=1669">Rome</a>, but ordered him, though it was in the middle of winter, to leave <a class="linkToPlace" target="_blank" href="/place?placename=Italy&groupId=656&placeId=1199">Italy</a> in a given number of days.
From all this it is obvious that there had been some approaches made to Eumenes by Perseus, which caused this marked estrangement on the part of the Romans.
As to what these were and how far they went it is open for us to inquire.
Walbank Commentary