Ecclesiastical History, Books 1-5

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 forty 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.

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