e success of any expedition against Parthia depended greatly on the
dispositions of the semi-dependent princes, who possessed territories
bordering upon those of the two great empires. Among these the most
important were at this time the kings of Armenia and Osrhoene. Armenia
had at the period of Niger's attempt been solicited by his emissaries;
but its monarch had then refused to take any part in the civil conflict.
Subsequently, however, he in some way offended Severus who, when he
reached the East, regarded Armenia as a hostile State requiring instant
subjugation. It seems to have been in the summer of A.D. 197, soon after
his first arrival in Syria, that Severus despatched a force against the
Armenian prince, who was named (like the Parthian monarch of the time)
Volagases. That prince mustered his troops and met the invaders at the
frontier of his kingdom. A battle seemed imminent; but ere the fortune
of war was tried the Armenian made an application for a truce, which
was granted by the Roman leaders. A breathing-space being thus gained,
Volagases sent ambassadors with presents and hostages to the Roman
emperor in Syria, professed to be animated by friendly feelings towards
Rome, and entreated Severus to allow him terms of peace. Severus
permitted himself to be persuaded; a formal treaty was made, and the
Armenian prince even received an enlargement of his previous territory
at the hands of his mollified suzerain.

The Osrhoenian monarch, who bore the usual name of Abgarus, made a more
complete and absolute submission. He came in person into the emperor's
camp, accompanied by a numerous body of archers, and bringing with
him his sons as hostages. Severus must have hailed with especial
satisfaction the adhesion of this chieftain, which secured him the
undisturbed possession of Western Mesopotamia as far as the junction of
the Khabour with the Euphrates. It was his design to proceed himself by
the Euphrates route, while he sent detachments under other leaders
to ravage Eastern Mesopotamia and Adiabene, which had evidently
been re-occupied by the Parthians. To secure his army from want, he
determined, like Trajan, to build a fleet of ships in Upper Mesopotamia,
where suitable timber abounded, and to march his army down the left
bank of the Euphrates into Babylonia, while his transports, laden with
stores, descended the course of the river. In this way he reached
the neighborhood of Ctesiphon without suffering any loss,