The Armenian Apostolic Church is one of the oldest Christian denominations in the world, tracing its roots back to the early 4th century. It was the first nation to adopt Christianity as its state religion in 301 AD, largely due to the efforts of Saint Gregory the Illuminator. The church follows the Apostolic tradition and emphasizes the importance of the sacraments. The church's structure is led by the Catholicos, who is the spiritual leader and head of the Armenian Church. Its teachings are based on the Bible and the writings of the early church fathers. The Armenian Apostolic Church also has a rich cultural heritage, including unique liturgical practices and a distinct architectural style in its churches.