Eusebius was commonly known among the ancients as Eusebius of Caesarea or Eusebius Pamphili. The first designation arose from the fact that he was bishop of Caesarea for many years; the second from the fact that he was a close friend and admirer of Pamphilus, a proselyte of Caesarea and a martyr. At least 40 contemporaries bore the same name, among which the most famous were Eusebius of Samosata—and so arose the necessity of distinguishing him from these others by specific designation.
The year of the Edict of Milan, which divides the first from the second epoch of Church history, does like service for the life and for the literary medium of the Church’s first historian. According to the growing assent of scholars, 313 marks off chronologically the Alexandrian from the Byzantine period of Greek literature, and it is 313 that cleaves into uneven but appropriate parts that career of Eusebius Pamphilil. In training and in literary taste, Eusebius belongs to the earlier time. Officially and in literary productivity, he belongs to the later. It was shortly after 313 that Eusebius became a bishop, as it was, for the most part, after 313 that his works were actually composed. Of events contemporary with these later years, Eusebius recorded much that is valued, but it is for what he tells of the earlier period—of the days before the Peace of the Church—that he looms so large in the history of history and of literature. Through him—through him almost alone—are preserved to us the feeble memories of an age that died with himself.