By the accession of Constantine to the sole sovereignty of the Roman Empire, A. D.324, ancient Christianity may be conveniently divided into two great periods. In the first, it was a religion liable to persecution, suffering severely at times and always struggling to maintain itself; in the second, it became the religion of the State, and in its turn set about to repress and persecute the heathen religions. It was no longer without legal rights; it had the support of the secular rulers and was lavishly endowed with wealth. The conditions of the Church in these two periods are so markedly different, and the conditions had such a distinct effect upon the life and growth of the Christian religion, that the reign of Constantine is universally recognized as marking a transition from one historical period to another, although no date which shall mark that transition is universally accepted. The year 311, the year in which the Diocletian persecution ceased, has been accepted by many as the dividing point. The exact date adopted is immaterial.

The principal sources in English for the history of the Christian Church before A. D.324 are:

The Ante-Nicene Fathers. Translations of the Writings of the Fathers down to A. D.325. American edition, Buffalo and New York, 1885-1896; new edition, New York, 1896 (a reprint). The collection, cited as ANF, contains the bulk of the Christian literature of the period, with the exception of the less important commentaries of Origen.

Eusebius, Church History. Translated with Prolegomena and Notes by Arthur Cushman McGiffert. In A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church. Second series, New York, 1890. The Church History of Eusebius is the foundation of the study of the history of the Church before A. D.324, as it contains a vast number of citations from works now lost. The edition by Professor McGiffert is the best in English, and is provided with scholarly notes, which serve as an elaborate commentary on the text. It should be in every library. This work is cited as Eusebius, Hist. Ec. The text used in the extracts given in this source book is that of Ed. Schwartz, in Die Griechischen Christlicher: Schriftsteller der ersten drei Jahrhunderte. Kleine Ausgabe, Leipsic, 1908. This text is identical with the larger and less convenient edition by the same editor.