Legio IIII Parthica: one of the Roman legions. Its name indicates that it was recruited to fight against the Parthians.
The name of this unit is a deliberate archaism: when it was created, the Parthian Empire, which had once threatened Rome's eastern frontier, had already been replaced by the Sasanian Empire.
This legion was created by the emperor Diocletian (284-305), who reorganized the eastern frontier of the Roman empire. The Fourth Parthian Legion occupied, together withh III Parthica, the region known as Osrhoene in western Mesopotamia. The capital of the region was Edessa and we may assume that its base was over there.
IIII Parthica is one of the last Roman army units whose existence is recorded. During the reign of the Byzantine emperor Maurice (582-602), the legion still existed. By then, its base was at Beroea (Aleppo).