But Rome was not to escape the Nemesis which is wont to pursue the over-fortunate.  During the stay of the army in Babylonia a disease was contracted of a strange and terrible character, whereto the superstitious fears of the soldiers assigned a supernatural origin.  The pestilence, they said, had crept forth from a subterranean cell in the temple of Comsean Apollo at Seleucia, which those who were plundering the town rashly opened in the hope of its containing treasure, but which held nothing except this fearful scourge, placed there in primeval times by the spells of the Chaldaeans.  Such a belief, however fanciful, was calculated to increase the destructive-power of the malady, and so to multiply its victims.  Vast numbers of the soldiers perished, we are told, from its effects during the march homeward; their sufferings being further aggravated by the failure of supplies, which was such that; many died of famine.  The stricken army, upon entering the Roman territory, communicated the infection to the inhabitants, and the return of Verus and his troops to Rome was a march of Death through the provinces.  The pestilence raged with special force throughout Italy, and spread as far as the Rhine and the Atlantic Ocean.  According to one writer more than one half of the entire population, and almost the whole Roman army, was carried off by it.

But though Rome suffered in consequence of the war, its general result was undoubtedly disadvantageous to the Parthians.  The expedition of Cassius was the first invasion of Parthia in which Rome had been altogether triumphant.  Trajan’s campaign had brought about the submission of Armenia to the Romans; but it did not permanently deprive Parthia of any portion of her actual territory.  And the successes of the Emperor in his advance were almost balanced by the disasters which accompanied his retreat—­disasters so serious as to cause a general belief that Hadrian’s concessions sprang more from prudence than from generosity.  The war of Verus produced the actual cession to Rome of a Parthian province, which continued thenceforth for centuries to be an integral portion of the Roman Empire.  Western Mesopotamia, or the tract between the Euphrates and the Khabour, passed under the dominion of Rome at this time; and, though not reduced to the condition of a province, was none the less lost to Parthia, and absorbed by Rome into her territory.  Parthia, moreover, was penetrated by the Roman arms more deeply at this time than she had ever been previously, and was made to feel, as she had never felt before, that in contending with Rome she was fighting a losing battle.  It added to the disgrace of her defeats, and to her own sense of their decisive character, that they were inflicted by a mere general, a man of no very great eminence, and one who was far from possessing the free command of those immense resources which Rome had at her disposal.