necessary for him, if he were to make head against his powerful rival, to draw together troops from all quarters.  Accordingly, towards the close of A.D. 193, he sent envoys to the princes beyond the Euphrates, and especially to the kings of Parthia, Armenia, and Hatra, entreating them to send their troops at once to his aid.  Volagases, under these circumstances, appears to have hesitated.  He sent an answer that he would issue orders to his satraps for the collection of a force, but made no haste to redeem his promise, and in fact refrained from despatching any body of distinctly Parthian troops to the assistance of Niger in the impending struggle.

While, however, thus abstaining from direct interference in the contest between the two Roman pretenders, Volagases appears to have allowed one of his dependent monarchs to mix himself up in the quarrel.  Hatra, at this time the capital of an Arabian community, and the chief city of central Mesopotamia (or the tract between the Sinjar and the Babylonian alluvium), was a dependency of Parthia, and though, like so many other Parthian dependencies, it possessed its native kings, cannot have been in a position to engage in a great war without permission from the Court of Ctesiphon.  When, therefore, we find that Barsemius, the King of Hatra, not only received the envoys of Niger favorably, but actually sent to his aid a body of archers, we must understand that Volagases sanctioned the measure.  Probably he thought it prudent to secure the friendship of the pretender whom he expected to be successful, but sought to effect this in the way that would compromise him least if the result of the struggle should be other than he looked for.  The sending of his own troops to the camp of Niger would have committed him irretrievably; but the actions of a vassal monarch might with some plausibility be disclaimed.

As the struggle between the two pretenders progressed in the early months of A.D. 194, the nations beyond the Euphrates grew bolder, and allowed themselves to indulge their natural feelings of hostility towards the Romans.  The newly subjected Mesopotamians flew to arms, massacred most of the Roman detachments stationed about their country, and laid siege to Nisibis, which since the cession Rome had made her head-quarters.  The natives of the region were assisted by their kindred races across the Tigris, particularly by the people of Adiabene, who, like the Arabs of Hatra, were Parthian vassals.  Severus had no sooner overcome his rival and slain him, than he hastened eastward with the object of relieving the troops shut up in Nisibis, and of chastising the rebels and their abettors.  It was in vain that the Mesopotamians sought to disarm his resentment by declaring that they had taken up arms in his cause, and had been only anxious to distress and injure the partisans of his antagonist.  Though they sent ambassadors to him with presents, and offered to make restitution of the Roman spoil still in their