Far more fraught with momentous effects than these new relations of the Romans to the Armenians, Iberians, Bosporans, and Nabataeans was the proximity into which through the occupation of Syria they were brought with the Parthian state.  Complaisant as had been the demeanour of Roman diplomacy towards Phraates while the Pontic and Armenian states still subsisted, willingly as both Lucullus and Pompeius had then conceded to him the possession of the regions beyond the Euphrates,(19) the new neighbour now sternly took up his position by the side of the Arsacids; and Phraates, if the royal art of forgetting his own faults allowed him, might well recall now the warning words of Mithradates that the Parthian by his alliance with the Occidentals against the kingdoms of kindred race paved the way first for their destruction and then for his own.  Romans and Parthians in league had brought Armenia to ruin; when it was overthrown, Rome true to her old policy now reversed the parts and favoured the humbled foe at the expense of the powerful ally.  The singular preference, which the father Tigranes experienced from Pompeius as contrasted with his son the ally and son-in-law of the Parthian king, was already part of this policy; it was a direct offence, when soon afterwards by the orders of Pompeius the younger Tigranes and his family were arrested and were not released even on Phraates interceding with the friendly general for his daughter and his son-in-law.  But Pompeius paused not here.  The province of Corduene, to which both Phraates and Tigranes laid claim, was at the command of Pompeius occupied by Roman troops for the latter, and the Parthians who were found in possession were driven beyond the frontier and pursued even as far as Arbela in Adiabene, without the government of Ctesiphon having even been previously heard (689).  Far the most suspicious circumstance however was, that the Romans seemed not at all inclined to respect the boundary of the Euphrates fixed by treaty.  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