The origin of Araratian Pontifical Diocese dates back the beginning of the 4th century. With the Christianzation of Armenia, Saint Gregory the Illuminator established the Catholicosate of All Armenians in Vagharshapat, as well as the Araratian Pontifical Diocese and appointed Bishop Albianus as the first primate vicar of the newly-founded diocese. The name of the diocese is derived from Mount Ararat; the symbol of the Armenian nation. At first, the diocese included the territories of Ararat plain, Nakhijevan, Kotayk and the western territories of Lake Sevan. It is believed that the diocese was commonly known as the Diocese of Yerevan between the 15th and 19th centuries. Under the Russian rule during the mid 19th century, the jurisdiction of the diocese was expanded to included the territories of Syunik and Shirak as well, followed by the area of Kars in 1878, covering almost the entire area of Eastern Armenia.