Osroes I

Osroes I ruled part of the Parthian Empire during the Roman invasion that nearly destroyed it, and his reign is the reason the invasion happened. He came to power around AD 109 in the west of the empire while Vologases III held the east, and the two fought each other for over a decade — a division that left neither able to concentrate against Rome. The pretext for war was Armenia. Under the settlement Nero had negotiated in AD 63, the king of Armenia was to be a Parthian prince invested by Rome, an arrangement that had kept the peace for half a century. Osroes deposed the sitting king and installed his own nephew Parthamasiris without Roman consent. Trajan treated it as a breach and marched east in AD 114. He annexed Armenia outright as a province. Parthamasiris came to him at Elegeia, laid his diadem at Trajan's feet expecting to receive it back, and was told the kingdom would not be given to anyone. He was killed shortly afterwards. Trajan then took Mesopotamia in two campaigns, entered Ctesiphon in AD 116, and reached the Persian Gulf, where Cassius Dio has him watch a ship sail for India and regret being too old to follow Alexander. The conquest collapsed almost immediately. Revolts broke out across the occupied territory and in the Jewish diaspora, and Trajan crowned a client king at Ctesiphon rather than hold it. Hadrian abandoned everything east of the Euphrates on his accession in AD 117. Osroes was defeated by Vologases and disappears around AD 129.

• Nationality: Parthian
• Roles: ruler