Addressing Phraataces by his bare name, without adding the title of king, he required him to lay aside the royal appellation, which he had arrogantly and without any warrant assumed, and at the same time to withdraw his forces from Armenia.

On the surrender of the Parthian princes he kept silence, ignoring a demand which he had no intention of according.

It was clearly his design to set up one of the elder brothers as a rival claimant to Phraataces, or at any rate to alarm him with the notion that, unless he made concessions, this policy would be adopted.
But Phraataces was not to be frightened by a mere message.

He responded to Augustus after his own fashion, dispatching to him a letter wherein he took to himself the favorite Parthian title of "king of kings," and addressed the Roman Emperor simply as "Caesar." The attitude of defiance would no doubt have been maintained, had Augustus confined himself to menaces; when, however, it appeared that active measures would be taken, when Augustus, in B.C.1, sent his grandson, Caius, to the East with orders to re-establish the Roman influence in Armenia even at the cost of a Parthian war, and that prince showed himself in Syria with all the magnificent surroundings of the Imperial dignity, the Parthian monarch became alarmed.

He had an interview with Caius in the spring of A.D.
1, upon an island in the Euphrates; where the terms of an arrangement between the two Empires were discussed and settled.