Armenia is the first country to have adopted Christianity as its state religion.
According to tradition, Armenia was evangelized by the apostles Bartholomew and Thaddeus. Armenia became the first country to adopt Christianity about 300 CE when St. Gregory the Illuminator converted the Arsacid king Tiridates III. The new Armenian church soon struck a course independent of the founding church at Caesarea Cappadocia (now Kayseri, Turkey), though it developed in close relationship with the Syrians, who provided it with scriptures and liturgy and much of its basic institutional terminology.
According to Eusebius (historian) and Tertullian (author), Armenian Christians were persecuted by kings Axidares, Khosrov I, and Tiridates III, the last of whom was converted to Christianity by Gregory the Illuminator. Ancient Armenia's adoption of Christianity as a state religion (the first state to do so) has been referred to by Nina Garsoïan as "probably the most crucial step in its history." This conversion distinguished it from its Iranian and Mazdean roots and protected it from further Parthian influence. According to Mary Boyce, the acceptance of Christianity by the Arsacid-Armenian rulers was partly in defiance of the Sassanids.