The Cathedral of Etchmiadzin, the earliest domed church, was built in AD 301-303 by King Trdat III (Tiridates) who’s reign was made memorable by the official conversion of Armenia to Christianity and St Gregory the Illuminator who was the successor of the two Apostles, Saints Thaddeus and Bartholomew.
The Armenians received the holy Religion of Christ through the Apostoles Saints Saints Thaddeus and Bartholomew, who preached the Gospel in Armenia and laid the foundation of the Church of Christ there.
The Church of Armenia was the first Christian Church established among the then heathen nations. Etchmiadzin became an Apostolic seat, and it has ever since been occupied by the Catholics of Holy Etchmiadzin, the Mother-see of the Armenian Church. It contains a miraculous picture of the Virgin with the infant, about which there is quite a literature of legendary lore. The design of the church is original, being in the general form of a Greek cross with a central cupola. It seems to have been build on the model of Sassanid structures (the Persian architectural style). The early frescoes inside the cathedral were restored in the 18th century.