Born in Caesarea, Eusebius studied under the director of the theological school in that city, Pamphilus (a future martyr), whom he so admired that he adopted his name, calling himself Eusebius Pamphili.

A devoted disciple of Origen, Pamphilus expanded the library that Origen had established at Caesarea and passed on to Eusebius the great master’s critical and scientific approach to texts. After Pamphilus’s martyrdom, Eusebius fled to Tyre and then to Egypt, where he may have been imprisoned for the faith.

When the persecution ended in 313 c.e., he returned to Caesarea and was made its bishop. As bishop of an important diocese—and one not far from Alexandria—Eusebius naturally became involved in the controversy of Arianism.

He was present at the Council of Nicaea in 325 and signed the Orthodox statement produced by the council known as the Nicene Creed, but he signed more for peacekeeping reasons than for a genuine conviction of its theological precision.

He was wary of the term homoousios (of one being), because he felt it smacked of Sabellianism (an earlier heresy that taught that the Trinity was three modes of being God, with no real distinction between Father, Son, and Holy Spirit).

After Nicaea, Eusebius became a leader of the moderate (or semi-Arian) party, which sought compromise and harmony over precise theological expression; this was a position favored also by the emperor Constantine the Great.

The oft-presented view that Eusebius enjoyed a close friendship with the emperor and was his trusted adviser has been criticized given their relatively few personal or literary exchanges.

It is more true that Eusebius’s uncritical admiration of the first Christian emperor—whom he believed God had sent to bring the church into an era of peace—enthusiastically colored his theology of the church with a certain triumphalism.

In spite of his tainted theological associations with the Arians and his biased treatment of Constantine, Eusebius will always be honored as the “Father of Ecclesiastical (Church) History.”

He is the first to attempt to compose a work chronicling the important people and events in the early church up to his own day, in c. 324. Entitled Church History, it is a rich collection of historical facts, documents, and excerpts from pagan and Christian authors, some of which are extant only in this work.

Some of the principal themes traced throughout the work are the list of bishops in the most important cities, Orthodox Christian writers and their defense of the faith up against the heresies of their day, the times of persecutions along with authentic stories of the martyrs and confessors in each of the periods, the fate of the Jews, and the development of the canonical books of the New Testament.

Although it contains a number of errors, the very “plethora of details” it gives and the eyewitness accounts of the persecutions and martyrdoms make it a work of inestimable value.

Eusebius is witness to an understanding of ecclesiology that is both rooted in tradition and energetically engaged in expressing the faith in terms called for by the shifting winds of time. Also, his candid approach to the canon of the New Testament allows the reader a splendid glimpse of early Christianity in the process of discerning an important issue.

Besides his Church History, Eusebius’s writings include Life of Constantine (an unfinished work, which is more of an encomium than a historical biography), apologetical works (against pagans and Jews), biblical works (including commentaries, a harmony of the Gospels, and a geographical dictionary of the Bible), dogmatic works (such as Defense of Origen), sermons, and a few extant letters.