Period I: The Imperial State Church Of The Undivided Empire, Or Until The Death Of Theodosius The Great, 395

The history of the Church in the first period of the second division of the history of ancient Christianity has to deal primarily with three lines of development, viz.: first, the relation of the Church to the imperial authority and the religious forces of the times, whereby the Church became established as the sole authorized religion of the Empire, and heathenism and heresy were prohibited by law; secondly, the development of the doctrinal system of the Church until the end of the Arian controversy, whereby the full and eternal deity of the Son was established as the Catholic faith; thirdly, the development of the constitution, the fixation of the leading ecclesiastical conceptions, and the adaptation of the system of the Church to the practical needs of the times. The entire period may be divided into two main parts by the reign of Julian the Apostate (361-363); and the reign of Constantine as Emperor of the West (312-324) may be regarded as a prelude to the main part of the history. On the death of Theodosius the Great in 395, the Empire became permanently divided, and though in the second period the courses of the Church in the East and in the West may be treated to some extent together, yet the fortunes, interests, and problems of the two divisions of the Church begin to diverge.