Soon after this, circumstances occurred in the border state of Commagene which threatened a rupture of the friendly relations that had hitherto subsisted between Volagases and Vespasian.  Caesennius Paetus, proconsul of Syria, the unsuccessful general in the late Armenian war, informed Vespasian, early in A.D. 72, that he had discovered a plot, by which Commagene, one of the Roman subject kingdoms, was to be detached from the Roman alliance, and made over to the Parthians.  Antiochus, the aged monarch, and his son Epiphanes were, according to Paetus, both concerned in the treason; and the arrangement with the Parthians was, he said, actually concluded.  It would be well to nip the evil in the bud.  If the transfer of territory once took place, a most serious disturbance of the Roman power would follow.  Commagene lay west of the Euphrates; and its capital city, Samosata (the modern Sumeisat), commanded one of the points where the great river was most easily crossed; so that, if the Parthians held it, they would have a ready access at all times to the Roman provinces of Cappadocia, Cilicia, and Syria, with a perfectly safe retreat.  These arguments had weight with Vespasian, who seems to have had entire confidence in Paetus, and induced him to give the proconsul full liberty to act as he thought best.  Thus empowered, Paetus at once invaded Commagene in force, and meeting at first with no resistance (for the Commagenians were either innocent or unprepared), succeeded in occupying Samosata by a coup de main.  The aged king wished to yield everything without a blow; but his two sons, Epiphanes and Callinicus, were not to be restrained.  They took arms, and, at the head of such a force as they could hastily muster, met Paetus in the field, and fought a battle with him which lasted the whole day, and ended without advantage to either side.  But the decision of Antiochus was not to be shaken; he refused to countenance his sons’ resistance, and, quitting Commagene, passed with his wife and daughters into the Roman province of Cilicia, where he took up his abode at Tarsus.  The spirit of the Commagenians could not hold out against this defection; the force collected began to disperse; and the young princes found themselves forced to fly, and to seek a refuge in Parthia, which they reached with only ten horsemen.  Volagases received them with the courtesy and hospitality due to their royal rank; but as he had given them no help in the struggle, so now he made no effort to reinstate them.  All the exertion to which he could be brought was to write a letter on their behalf to Vespasian, in which he probably declared them guiltless of the charges that had been brought against them by Paetus.  Vespasian, at any rate, seems to have become convinced of their innocence; for though he allowed Commagene to remain a Roman province, he permitted the two princes with their father to reside at Rome, assigned the ex-monarch an ample revenue, and gave the family an honorable status.