According to Dio, the first engagement was brought on accidentally by a contest which arose among the soldiers for the possession of a watering-place.  Herodian tells us that it commenced with a fierce assault of the Parthian cavalry, who charged the Romans with loud shouts, and poured into their ranks flight after flight of arrows.  A long struggle followed.  The Romans suffered greatly from the bows of the horse-archers, and from the lances of the corps mounted on camels; and though, when they could reach their enemy, they had always the superiority in close combat, yet after a while their losses from the cavalry and camels forced them to retreat.  As they retired they strewed the ground with spiked balls and other contrivances for injuring the feet of animals; and this stratagem was so far successful that the pursuers soon found themselves in difficulties, and the armies respectively retired, without any decisive result, to their camps.

The next day there was again a combat from morning to night, of which we have no description, but which equally terminated without any clear advantage to either side.  The fight was then renewed for the third time on the third day, with the difference that the Parthians now directed all their efforts towards surrounding the enemy, and thus capturing their entire force.  As they greatly outnumbered the Romans, these last found themselves compelled to extend their line unduly, in order to meet the Parthian tactics; and the weakness of the extended line seems to have given the Parthians an opportunity of throwing it into confusion, and thus causing the Roman defeat.  Macrinus took to flight among the first; and his hasty retreat discouraged his troops, who soon afterwards acknowledged themselves beaten, and retired within the lines of their camp.  Both armies had suffered severely.  Herodian describes the heaps of dead as piled to such a height that the manoeuvres of the troops were impeded by them, and at last the two contending hosts could scarcely see one another!  Both armies, therefore, desired peace.  The soldiers of Macrinus, who had never had much confidence in their leader, were demoralized by ill success, and showed themselves inclined to throw off the restraints of discipline.  Those of Artabanus, a militia rather than a standing force, were unaccustomed to sustained efforts; and having been now for some months in the field, had grown weary, and wished to return home.  Macrinus under these circumstances re-opened negotiations with his adversary.  He was prepared to concede something more than he had proposed originally, and he had reason to believe that the Parthian monarch, having found the Roman resistance so stubborn, would be content to insist on less.  The event justified his expectations.  Artabanus relinquished his demand for the cession of Mesopotamia, and accepted a pecuniary compensation for his wrongs.  Besides restoring the captives and the booty carried off by Caracallus in his raid, Macrinus had to pay a sum exceeding a million and a half of our money.  Rome thus concluded her transactions with Parthia, after nearly three centuries of struggle, by ignominiously purchasing a peace.