Mirian III () was a king of Iberia or Kartli (Georgia), contemporaneous to the Roman emperor Constantine the Great (r. 306–337). He was the founder of the royal Chosroid dynasty. According to the early medieval Georgian annals and hagiography, Mirian was the first Christian king of Iberia, converted through the ministry of Nino, a Cappadocian female missionary. After Christianization of Iberia he is credited with establishment of Christianity as his kingdom's state religion and is regarded by the Georgian Orthodox Church as saint and is canonized as Saint Equal to the Apostles King Mirian (). Traditional chronology after Prince Vakhushti assigns to Mirian's reign—taken to have lasted for 77 years—the dates 268–345, which Professor Cyril Toumanoff corrects to 284–361. He is also known to the contemporary Roman historian Ammianus Marcellinus and the medieval Armenian chronicles. Name "Mirian" is the Georgian form of the Iranian name of Mihrān. The name is transliterated in Greek as Mithranes. According to the Life of Vakhtang, his name was also associated with Mirdat, meaning "given by Mithra", the name of the ancient Iranian sun god. His name is rendered as Meribanes by the Roman historian Ammianus Marcellinus (XXI, 6, 8). The regnal numbers as in Mirian III are modern and were not used by the medieval Georgian authors. Since two kings preceded him with that name, Mirian has been assigned the ordinal "III" in Georgian historiography. Background and accession Mirian was a member of the House of Mihran, one of the Seven Great Houses of Iran. The family, based at Ray in northern Iran, traced its ancestry back to the ruling Arsacid Empire, the predecessors of the Sasanian Empire. Mirian himself was also born in Iran and was originally a Zoroastrian. In 284, the Sasanian King of Kings (shahanshah) Bahram II () secured the Iberian throne for Mirian, which laid the foundation for Mihranid rule in Iberia, which would last into the sixth century. Thus, the Chosroid dynasty of which Mirian became its first head, was a branch of the Mihranid princely family. The motive behind Bahram II's move was to strengthen Sasanian authority in the Caucasus and utilize the position of the Iberian capital Mtskheta as an entrance to the important passes through the Caucasus Mountains. This was of so high importance to Bahram II, that he allegedly himself went to Mtskheta in order to secure Mirian's position. He also sent one of his