Eusebius of Caesarea (c. 260 – c. 341) was the most significant of the early historians of the church. His Ecclesiastical History was a chronicle of Christianity from Jesus to Constantine’s success in taking over the Roman Empire. Eusebius himself played a role in the most significant event of Christianity in the fourth century. As the bishop of Caesarea, Eusebius was one of the leaders of the semi-Arian party. He wrote about the events of his own day in his Life of Constantine. As historian and participant, Eusebius was vital to the transition of the Christian church from proscribed sect to dominant religion.