Volagases had taken up his own position at Ctesiphon, bent on defending his capital.  It is possible that the approach of Severus by the line of march which he pursued was unexpected, and that the sudden presence of the Romans before the walls of Ctesiphon came upon the Parthian monarch as a surprise.  He seems, at any rate, to have made but a poor resistance.  It may be gathered, indeed, from one author that he met the invaders in the open field, and fought a battle in defence of Ctesiphon before allowing himself to be shut up within its walls.  But after the city was once invested it appears to have been quickly taken.  We hear of no such resistance as that which was soon afterwards offered by Hatra.  The soldiers of Severus succeeded in storming Ctesiphon on the first assault; the Parthian monarch betook himself to flight, accompanied by a few horsemen; and the seat of empire thus fell easily—­a second time within the space of eighty-two years—­into the hands of a foreign invader.  The treatment of the city was such as we might expect from the ordinary character of Roman warfare.  A general massacre of the male population was made.  The soldiers wore allowed to plunder both the public and the private buildings at their pleasure.  The precious metals accumulated in the royal treasury were seized, and the chief ornaments of the palace were taken and carried off.  Nor did blood and plunder content the victors.  After slaughtering the adult males they made prize of the women and children, who were torn from their homes without compunction and led into captivity, to the number of a hundred thousand.

Notwithstanding the precautions which he had taken, Severus appears to have become straitened for supplies about the time that he captured Ctesiphon.  His soldiers were compelled for some days to exist on roots, which produced a dangerous dysentery.  He found himself unable to pursue Volagases, and recognized the necessity of retreating before disaster overtook him.  He could not, however, return by the route of the Euphrates, since his army had upon its advance completely exhausted the resources of the Euphrates region.  The line of the Tigris was therefore preferred for the retreat; and while the ships with difficulty made their way up the course of the stream, the army pursued its march upon the banks, without, so far as appears, any molestation.  It happened, however, that the route selected led Severus near to the small state of Hatra, which had given him special offence by supporting the cause of his rival, Niger; and it seemed to him of importance that the inhabitants should receive condign punishment for this act of audacity.  He may also have hoped to eclipse the fame of Trajan by the capture of a town which had successfully resisted that hero.  He therefore stopped his march in order to lay siege to the place, which he attacked with military engines, and with all the other offensive means known at the time to the Romans.  His first