The trend towards moralising historiography continued with Polybius who used his sources to underpin his theories on government. These later Greek historians tended to see the need for history to be instructive; they used their sources to construct theories on morals and politics, which led to Greek history eventually being overtaken by philosophy.
Although the Roman historians modelled their writing on their Greek forerunners the quality of their work tended to be of a lesser standard with the possible exception of Tacitus. Caesar had an accessible style but he moulded his accounts of the past to glorify his own achievements while Livy introduced myth and legend in order to make his writing more entertaining. With the decline of the Roman Empire and the military and political history it had generated came the rise of Christianity and a new style of historiography.
Christian history was inevitably propagandist. The purpose of history had changed; it was now a weapon to oppose paganism. Historians of the Christian period such as Martin of Tours found in their study of the past, examples of divine intervention in the world and wrote history replete with miracles and disasters designed to convince readers of the greatness of their Christian God. Even Bede, who, for his time, was rigorous in his historical method, who searched out and scrupulously named all his sources, even he, marshalled his sources with the express intention of teaching the message of the true faith. As a monk he was also dependent on the secular power of the day and the fact that his Historia ecclesiastica gentis Anglorum is dedicated to the Northumbrian king Ceolwulf is a clue to the Northumbrian, Anglo-Saxon bias in his work.