|The Etchmiadzin Cathedral, the mother church of the Armenian Apostolic Church, was established in 301 AD.|
In 301 AD, Armenia adopted Christianity as a state religion, becoming the first state to do so. The claim is primarily based on the fifth-century work of Agathangelos titled “The History of the Armenians.” Agathangelos witnessed at first hand the baptism of the Armenian King Trdat III (c. 301/314 A.D.) by St. Gregory the Illuminator. Trdat III decreed Christianity was the state religion.
Armenia established a Church that still exists independently of both the Catholic and the Eastern Orthodox churches, having become so in 451 AD as a result of its stance regarding the Council of Chalcedon. Today this church is known as the Armenian Apostolic Church, which is a part of the Oriental Orthodox communion, not to be confused with the Eastern Orthodox communion. During its later political eclipses, Armenia depended on the church to preserve and protect its unique identity. The original location of the Armenian Catholicosate is Echmiadzin. However, the continuous upheavals, which characterized the political scenes of Armenia, made the political power move to safer places. The Church center moved as well to different locations together with the political authority. Therefore, it eventually moved to Cilicia as the Holy See of Cilicia.
The Armenians collective has, at times, constituted a Christian "island" in a mostly Muslim region. There is, however, a minority of ethnic Armenian Muslims, known as Hamshenis but many Armenians view them as a separate race, while the history of the Jews in Armenia dates back 2,000 years. The Armenian Kingdom of Cilicia had close ties to European Crusader States. Later on, the deteriorating situation in the region led the bishops of Armenia to elect a Catholicos in Etchmiadzin, the original seat of the Catholicosate. In 1441, a new Catholicos was elected in Etchmiadzin in the person of Kirakos Virapetsi, while Krikor Moussapegiants preserved his title as Catholicos of Cilicia. Therefore, since 1441, there have been two Catholicosates in the Armenian Church with equal rights and privileges, and with their respective jurisdictions. The primacy of honor of the Catholicosate of Etchmiadzin has always been recognized by the Catholicosate of Cilicia.
While the Armenian Apostolic Church remains the most prominent church in the Armenian community throughout the world, Armenians (especially in the diaspora) subscribe to any number of other Christian denominations. These include the Armenian Catholic Church (which follows its own liturgy but recognizes the Roman Catholic Pope), the Armenian Evangelical Church, which started as a reformation in the Mother church but later broke away, and the Armenian Brotherhood Church, which was born in the Armenian Evangelical Church, but later broke apart from it. There are other numerous Armenian churches belonging to Protestant denominations of all kinds.
Through the ages many Armenians have collectively belonged to other faiths or Christian movements, including the Paulicians which is a form of Gnostic and Manichaean Christianity. Paulicians sought to restore the pure Christianity of Paul and in c.660 founded the first congregation in Kibossa, Armenia.
Another example is the Tondrakians, who flourished in medieval Armenia between the early 9th century and 11th century. Tondrakians advocated the abolishment of the church, denied the immortality of the soul, did not believe in an afterlife, supported property rights for peasants, and equality between men and women.
The Orthodox Armenians or the Chalcedonian Armenians in the Byzantine Empire were called Iberians ("Georgians") or "Greeks". See Gregory Pakourianos – the great Byzantine general. Their descendants are the Hayhurum and Catholic Armenians in Georgia.