Legio V Parthica

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archaism: when it was created, the Parthian empire, which had once threatened Rome's eastern frontier, had already been replaced by the Sasanian empire.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. According to Ammianus Marcellinus,^note[Ammianus Marcellinus, Roman History 18.9.3.] the Fifth Parthian legion, "along with a force of no mean size of natives", was stationed at Amida (modern Diyarbakır), the site of an important bridge across the Tigris, along the ancient road from Central Anatolia to Assyria.

When the city was attacked by the Persians in 359, it was unable to defend the town, even though it was reinforced with six additional legions. It was probably not reconstituted after its defeat, because it is not mentioned in the catalogue of late-fourth century military units that is included in the Notitia Dignitatum.