Throughout most of its history during this period, under the reign of the Arsacid dynasty, the Armenian nobility was divided among Roman-loyalists, Parthian-loyalists, and neutrals.

Towards the middle of the 1st century AD, the rising Parthian influence disputed Roman supremacy, which was re-established by the campaigns of Gnaeus Domitius Corbulo.

[2] This conflict ended after the Battle of Rhandeia, in an effective stalemate and a formal compromise: a Parthian prince of the Arsacid line would henceforth sit on the Armenian throne, but his nomination had to be approved by the Roman emperor.

Trajan then deposed the Armenian king Parthamasiris and ordered the annexation of Armenia to the Roman Empire as a new province.

The new province reached the shores of the Caspian Sea and bordered to the north with the Caucasian Iberia and Albania, two vassal states of Rome.

A rebellion by the Parthian pretender Sanatruces was put down, though sporadic resistance continued and Vologases III of Parthia managed to secure an area of south-eastern Armenia just before Trajan's death in August 117.

Parthamaspates was soon defeated by the Parthians, and again fled to the Romans, who granted him the co-rule of Osroene in western Greater Armenia as a consolation.

Armenia was in frequent dispute between the two empires and their candidates for the Armenian throne, a situation which lasted until the emergence of a new power, the Sasanians.

Rome's power and influence increased over the years since, but Armenia retained its independence, even if only as a vassal state, although it was a Roman ally against the Sasanian Empire.

[10] The satrapies in the south on the other hand, which had been under Roman influence already since 298, were a group of six fully autonomous principalities allied to the Empire (civitates foederatae): Ingilene, Sophene, Antzitene, Asthianene, Sophanene and Balabitene.

[11] The local Armenian nakharar were fully sovereign in their territories, and were merely required to provide soldiers upon request and to dispatch a golden crown to the emperor, as a token of submission.

In its aftermath, the satraps were stripped of their sovereignty and their rights of hereditary succession, being in effect reduced to the status of tax-paying and imperially-administered civitates stipendariae.

[citation needed] In 591, the treaty between Khosrow II and Maurice ceded most of Persarmenia to the Eastern Roman Empire.

With the ebbing of the Caliphate's power and the fracturing of its outlying territories into autonomous statelets, the Byzantines were able to re-assert their influence over the Armenian principalities during the campaigns of John Kourkouas in the early 10th century.

As a consequence of Diocletian's victory over the Sassanids, all of Armenia was once again a vassal state of Rome by 299: Rome secured in this way a wide zone of cultural influence east of Anatolia, which led to a wide diffusion of Syriac Christianity from a center at Nisibis in the first decades of the 4th century, and to the eventual full Christianization of Armenia.