Trajan's Parthian campaign was engaged by Roman Emperor Trajan in 115 against the Parthian Empire in Mesopotamia. The war was initially successful for the Romans, but a series of setbacks, including wide-scale rebellions in the Eastern Mediterranean and North Africa and Trajan's death in 117, ended in a Roman withdrawal.

In 113, Trajan decided that the moment was ripe for a final resolution of the "eastern question" by the decisive defeat of Parthia and the annexation of Armenia. His conquests marked a deliberate change of Roman policy towards Parthia and a shift of emphasis in the empire's "grand strategy". In 114, Trajan invaded Armenia; annexed it as a Roman province and killed Parthamasiris, who had been placed on the Armenian throne by his relative, Parthia King Osroes I.

In 115, the Roman emperor overran northern Mesopotamia and annexed it to Rome as well. Its conquest was deemed necessary since otherwise, the Armenian salient could be cut off by the Parthians from the south. The Romans then captured the Parthian capital, Ctesiphon, before they sailed downriver to the Persian Gulf.

However, revolts erupted that year in the Eastern Mediterranean, North Africa and northern Mesopotamia, while a major Jewish revolt broke out in Roman territory, which severely stretched Roman military resources. Trajan failed to take Hatra, which avoided a total Parthian defeat. Parthian forces attacked key Roman positions, and Roman garrisons at Seleucia, Nisibis and Edessa were evicted by the local populaces. Trajan subdued the rebels in Mesopotamia; installed a Parthian prince, Parthamaspates, as a client ruler and withdrew to Syria. Trajan died in 117 before he could renew the war