Parthia had now, in fact, entered upon the third stage of her decline.  The first was reached when she ceased to be an aggressive and was content to become a stationary power; the second set in when she began to lose territory by the revolt of her own subjects; the third—­which commences at this point—­is marked by her inability to protect herself from the attacks of a foreign assailant.  The causes of her decline were various.  Luxury had no doubt done its ordinary work upon the conquerors of rich and highly-civilized regions, softening down their original ferocity, and rendering them at once less robust in frame and less bold and venturesome in character.

The natural law of exhaustion, which sooner or later affects all races of any distinction, may also not improbably have come into play, rendering the Parthians of the age of Verus very degenerate descendants of those who displayed such brilliant qualities when they contended with Crassus and Mark Antony.  Loyalty towards the monarch, and the absolute devotion of every energy to his service, which characterized, the earlier times, dwindled and disappeared as the succession became more and more disputed, and the kings less worthy of their subjects’ admiration.  The strength needed against foreign enemies was, moreover, frequently expended in civil broils; the spirit of patriotism declined; and tameness under insult and indignity took the place of that fierce pride and fiery self-assertion which had once characterized the people.

The war with Rome terminated in the year A.D. 165.  Volagases survived its close for at least twenty-five years; but he did not venture at any time to renew the struggle, or to make any effort for the recovery of his lost territory.  Once only does he appear to have contemplated an outbreak.  When, about the year A.D. 174 or 175, Aurelius being occupied in the west with repelling the attacks of the wild tribes upon the Danube, Avidius Cassius assumed the purple in Syria, and a civil war seemed to be imminent, Volagases appears to have shown an intention of once more taking arms and trying his fortune.  A Parthian war was at this time expected to break out by the Romans.  But the crisis passed without an actual explosion.  The promptness of Aurelius, who, on hearing the news, at once quitted the Danube and marched into Syria, together with the rapid collapse of the Cassian revolt, rendered it imprudent for Volagases to persist in his project.  He therefore laid aside all thought of renewing hostilities with Rome; and, on the arrival of Aurelius in Syria, sent ambassadors to him with friendly assurances, who were received favorably by the philosophic Emperor.