Armenian tradition dates the church's founding to the first century missions of the apostles Thaddeus and Bartholomew, from whom it takes the name Apostolic, but its decisive moment came in the early fourth century. Gregory the Illuminator, imprisoned for years by King Tiridates III for refusing to worship pagan deities, is credited with converting the king after healing him from an illness attributed to his persecution of Christians. Tiridates then made Christianity the state religion of Armenia around 301, commonly cited as the earliest formal adoption of Christianity by any state, predating the Roman Empire's turn under Constantine by more than a decade.
The church's independence was reinforced by language as much as by politics. Around 405 the monk Mesrop Mashtots devised a dedicated Armenian alphabet, commissioned so scripture and liturgy could be rendered in the vernacular rather than only in Greek or Syriac, and the resulting translation of the Bible is still admired for its literary quality. The alphabet gave Armenian Christianity a textual and educational culture entirely its own, centered on monastic schools that produced chronicles, hymnody and theology for the following fifteen centuries.
Armenia's geographic position between the Byzantine and Persian, later Byzantine and Islamic, worlds made the church a marker of national identity under successive foreign rulers, a role its distinct alphabet and independent doctrine only deepened.