On several occasions Roman divisions destined from Armenia for Syria marched across Mesopotamia; the Arab emir Abgarus of Osrhoene was received under singularly favourable conditions into Roman protection; nay, Oruros, situated in Upper Mesopotamia somewhere between Nisibis and the Tigris 220 miles eastward from the Commagenian passage of the Euphrates, was designated as the eastern limit of the Roman dominion-- presumably their indirect dominion, inasmuch as the larger and more fertile northern half of Mesopotamia had been assigned by the Romans in like manner with Corduene to the Armenian empire.
The boundary between Romans and Parthians thus became the great Syro-Mesopotamian desert instead of the Euphrates; and this too seemed only provisional.

To the Parthian envoys, who came to insist on the maintenance of the agreements--which certainly, as it would seem, were only concluded orally--respecting the Euphrates boundary, Pompeius gave the ambiguous reply that the territory of Rome extended as far as her rights.

The remarkable intercourse between the Roman commander-in-chief and the Parthian satraps of the region of Media and even of the distant province Elymais (between Susiana, Media, and Persia, in the modern Luristan) seemed a commentary on this speech.( 20) The viceroys of this latter mountainous, warlike, and remote land had always exerted themselves to acquire a position independent of the great-king; it was the more offensive and menacing to the Parthian government, when Pompeius accepted the proffered homage of this dynast.
Not less significant was the fact that the title of "king of kings," which had been hitherto conceded to the Parthian king by the Romans in official intercourse, was now all at once exchanged by them for the simple title of king.

This was even more a threat than a violation of etiquette.

Since Rome had entered on the heritage of the Seleucids, it seemed almost as if the Romans had a mind to revert at a convenient moment to those old times, when all Iran and Turan were ruled from Antioch, and there was as yet no Parthian empire but merely a Parthian satrapy.