The History of the Church from Christ to Constantine, written by Eusebius of Caesarea (c. 260–339 AD), is the first comprehensive narrative of the Christian Church's development from its apostolic origins to its 4th-century triumph under Emperor Constantine. Known as the 'Father of Church History', Eusebius used his access to the vast Theological Library of Caesarea to preserve a massive collection of primary sources—letters, martyr acts, and imperial edicts—many of which would otherwise be lost.