Adiabene is an Assyrian vassal kingdom of the Parthian empire, with its capital at Arbela (modern-day Arbil, Iraq).

Despite the overthrow of the Parthians by the Sassanids in 224 CE, the feudatory dynasties remain loyal to the Parthians, and resist Sassanid advance into Adiabene and Atropatene.

Due to this, and religious differences, Adiabene is never regarded as an integral part of Iran, even though the Sassanids control it for several centuries.After the Roman Empire gradually makes Christianity its official religion during the fourth century, the inhabitants of Adiabene, who are Assyrian Christians, side with Christian Rome rather than the Zoroastrian Sassanids.

The East Roman (Byzantine) Empire sends armies to the region during the Byzantine-Sassanid Wars, but this does nothing to change the territorial boundaries.

Adiabene remains a province of the Sassanid Empire until the Islamic conquests of Persia.