Meanwhile the aged Sanatroeces died, and was succeeded by his son, Phraates III.  This prince followed at first his father’s example, and abstained from mixing himself up in the Mithridatic war; but in B.C. 66, being courted by both sides, and promised the restoration of the provinces lost to Tigranes, he made alliance with Pompey, and undertook, while the latter pressed the war against Mithridates, to find occupation for the Armenian monarch in his own land.  This engagement he executed with fidelity.  It had happened that the eldest living son of Tigranes, a prince bearing the same name as his father, having raised a rebellion in Armenia and been defeated, had taken refuge in Parthia with Phraates.  Phraates determined to take advantage of this circumstance.  The young Tigranes was supported by a party among his countrymen who wished to see a youthful monarch upon the throne; and Phraates therefore considered that he would best discharge his obligations to the Romans by fomenting this family quarrel, and lending a moderate support to the younger Tigranes against his father.  He marched an army into Armenia in the interest of the young prince, overran the open country, and advanced on Artaxata, the capital.  Tigranes, the king, fled at his approach, and betook himself to the neighboring mountains.  Artaxata was invested; but as the siege promised to be long, the Parthian monarch after a time withdrew, leaving the pretender with as many troops as he thought necessary to press the siege to a successful issue.  The result, however, disappointed his expectations.  Scarcely was Phraates gone, when the old king fell upon his son, defeated him, and drove him beyond his borders.  He was forced, however, soon afterwards, to submit to Pompey, who, while the civil war was raging in Armenia, had defeated Mithridates and driven him to take refuge in the Tauric Chersonese.

Phraates, now, naturally expected the due reward of his services, according to the stipulations of his agreement with Pompey.  But that general was either dissatisfied with the mode in which the Parthian had discharged his obligations, or disinclined to strengthen the power which he saw to be the only one in these parts capable of disputing with Rome the headship of Asia.  He could scarcely prevent, and he does not seem to have tried to prevent, the recovery of Adiabene by the Parthians; but the nearer province of Gordyene to which they had an equal claim, he would by no means consent to their occupying.  At first he destined it for the younger Tigranes.  When the prince offended him, he made it over to Ariobarzanes, the Cappadocian monarch.  That arrangement not taking effect, and the tract being disputed between Phraates and the elder Tigranes, he sent his legate, Afranius, to drive the Parthians out of the country, and delivered it over into the hands of the Armenians.  At the same time he insulted the Parthian monarch by refusing him his generally recognized title of “King of Kings.”  He thus entirely alienated his late ally, who remonstrated against the injustice with which he was treated, and was only deterred from declaring war by the wholesome fear which he entertained of the Roman arms.