The Treaty of Rhandeia was a peace treaty concluded between the Roman Empire and the Parthian Empire at the frontier town of Rhandeia in what is now Turkey in 63 CE. The treaty, which finalized the Roman–Parthian War of 58–63, stipulated that henceforth a Parthian prince of the Arsacid line would sit on the Armenian throne, but his nomination, or right of investiture, was given to the emperor of Rome.^[1][2] Even though this essentially made Armenia a de jure client kingdom of Rome in, various contemporary Roman sources thought that Nero had de facto ceded Armenia to the Parthian Empire through this treaty.^[3] This compromise between Parthia and Rome lasted for several decades, until 114 CE, when Rome under Trajan broke the peace by invading Armenia and subsequently Parthia itself, taking direct control of Arsacid Armenia and incorporating it into a short-lived Roman province which lasted for a mere four years before it was outwardly relinquished under Trajan's successor Hadrian in 118 CE.^[2]

The Arsacid dynasty would nevertheless maintain the Armenian throne, albeit most often as client kings, until 428 CE, when the kingdom was partitioned by the Eastern Roman and Sasanian empires, and the eastern part of Armenia became a Sasanian province from then on ruled by a marzban.^[4]