When Eusebius (c. A.D. 260-340) wrote his Ecclesiastical History, his vital concern was to record facts before they disappeared and before eyewitnesses were killed and libraries were burned and destroyed in persecutions by Rome. He faithfully transcribed the most important existing documents of his day so that future generations would have a collection of factual data to interpret. Thus Eusebius richly deserves the title Father of Church History.
Eusebius' Ecclesiastical History is one of the classics of early Christianity and of equal stature with the works of Flavius Josephus. Eusebius chronicles the events of the first three centuries of the Christian Church in such a way as to record a vast number of vital facts about early Christianity that can be learned from no other ancient source.
Eusebius of Caesarea (circa 260-340 AD), studied under Bishop Pamphilius of Caesarea, who was at that time the foremost authority on the Bible, closely following the teachings of Origen. During the Great Persecution of Christians started by Emperor Diocletian in 303, Eusebius began accumulating what would later become his magnum opus, Historia Ecclesiastica, salvaging many Christian manuscripts from obliteration. Although Eusebius himself survived the Great Persecution, his teacher Pamphilius would be imprisoned and eventually martyred.