Together with its twin legions I Parthica and II Parthica, the third Parthian legion was levied for the attack on the eastern frontier. The campaign was a success and Ctesiphon, the Parthian capital was taken and sacked. III Parthica remained in the region afterwards, garrisoning the new province of Mesopotamia. Their main base camp was Rhesaena, where they had the duty of securing the main roads and protect the province against the Sassanidss. During the 3rd century, III Parthica took part in several other campaigns against the Parthians. In the early 5th century, the legion was still active in the region.
See also: List of Roman legions