Christian historiography began early, perhaps as early as Luke-Acts, which is the primary source for the Apostolic Age, though its historical reliability is disputed. In the first Christian centuries, the New Testament canon was developed. The growth of Christianity and its enhanced status in the Roman Empire after Constantine I (see State church of the Roman Empire) led to the development of a distinct Christian historiography, influenced by both Christian theology and the nature of the Christian Bible, encompassing new areas of study and views of history. The central role of the Bible in Christianity is reflected in the preference of Christian historians for written sources, compared to the classical historians' preference for oral sources and is also reflected in the inclusion of politically unimportant people. Christian historians also focused on development of religion and society. This can be seen in the extensive inclusion of written sources in the "Ecclesiastical History" written by Eusebius of Caesarea around 324 and in the subjects it covers. Christian theology considered time as linear, progressing according to divine plan. As God's plan encompassed everyone, Christian histories in this period had a universal approach. For example, Christian writers often included summaries of important historical events prior to the period covered by the work.