In 109, Osroes I revolted against Parthian king
Pacorus II () in order to claim the throne for himself. During the reign of Pacorus II's son
Vologases III (), Osroes I managed to seize the western part of the empire, including
Mesopotamia, while Vologases III ruled in the east. In 113, Osroes I violated the
Treaty of Rhandeia with the
Romans by deposing Vologases III's brother
Axidares and appointing the latter's brother
Parthamasiris as the king of
Armenia. This gave the Roman emperor
Trajan () the
pretext to invade the Parthian domain and take advantage of the ongoing civil war between Vologases III and Osroes I. In 114, Trajan conquered Armenia and turned it into a Roman province. In 116, Trajan captured
Seleucia and
Ctesiphon, the capitals of the Parthians. Trajan even reached as far as the
Persian Gulf, where he forced the Parthian vassal ruler of
Characene,
Attambelos VII, to pay tribute. Fearing a revolt by the Parthians, Trajan installed Osroes I's son
Parthamaspates on the throne at Ctesiphon. During his expedition, Trajan captured a daughter of Osroes I, who remained a Roman captive until the peace treaty concluded between the two powers in 129. The gains of Trajan were short-lived. Revolts occurred in all the conquered territories, with the
Babylonians and
Jews pushing the Romans out of Mesopotamia, and the Armenians under Sanatruk causing the Romans problems. After Trajan's death in 117, the Parthians removed Parthamaspates from the throne and reinstated Osroes I. Trajan's successor,
Hadrian () renounced the remnants of Trajan's conquests in the east, and acknowledged the
Treaty of Rhandeia, with the Parthian prince
Vologases becoming the new king of Armenia. The weakened state of the western part of the Parthian Empire gave Vologases III (whose eastern domains were untouched) the opportunity to regain lost territory seized by Osroes I. In 129, Vologases III finally managed to remove Osroes I from power. == Coinage==