Parthian Empire
Osroene was generally allied with the Parthian Empire. After a period under the rule of the Parthian Empire, it was absorbed into the Roman Empire in 114 as a semiautonomous vassal state, and incorporated as a simple Roman province in 214. There is an apocryphal legend that Osroene was the first state to have accepted Christianity as state religion, but there is not enough evidence to support that claim.