After the fall of the Arsacid dynasty in Persia, the succeeding Sasanian Empire aspired to reestablish Persian control. The Sassanid Persians occupied Armenia in 252. However, in 287, Tiridates III the Great was established King of Armenia by the Roman armies. After Gregory the Illuminator's spreading of Christianity in Armenia, Tiridates accepted Christianity and made it his kingdom's official religion. The traditional date for Armenia's conversion to Christianity is established at 301, preceding the Roman Emperor Constantine the Great's conversion and the Edict of Milan by a dozen years.