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Eusebius of Caesarea (; Greek: Εὐσέβιος τῆς Καισαρείας, Eusébios tés Kaisareías; AD 260/265 – 339/340), also known as Eusebius Pamphili (from the Greek: Εὐσέβιος τοῦ Παμϕίλου), was a historian of Christianity, exegete, and Christian polemicist. He became the bishop of Caesarea Maritima about 314 AD. Together with Pamphilus, he was a scholar of the Biblical canon and is regarded as an extremely learned Christian of his time. He wrote Demonstrations of the Gospel, Preparations for the Gospel, and On Discrepancies between the Gospels, studies of the Biblical text. As "Father of Church History" (not to be confused with the title of Church Father), he produced the Ecclesiastical History, On the Life of Pamphilus, the Chronicle and On the Martyrs.

During the Council of Antiochia (325) he was excommunicated for subscribing to the heresy of Arius, and thus withdrawn during the First Council of Nicaea where he accepted that the Homoousion referred to the Logos. Never recognized as a saint, he became counselor of Constantine the Great, and with the bishop of Nicomedia he continued to polemicize against Saint Athanasius of Alexandria, Church Fathers, since he was condemned in the First Council of Tyre in 335.