Eusebius
A.D. 260 - 340
Eusebius lived through the Great Persecution under Diocletian and served as the bishop of Caesarea during the reign of Constantine. He was one of the bishops present at the Council of Nicaea. He is best known for writing his Ecclesiastical History.
When he wrote his History, Eusebius' vital concern was to record facts before they disappeared and before eyewitnesses might be killed and libraries might be burned during the next persecution. He faithfully transcribed the most important existing documents of his day, enabling later generations to have a collection of factual history about the first three centuries of Christianity.
Eusebius' Ecclesiastical History is one of the classics of early Christianity and stands in equal stature with the historical works of Josephus.