If historiography is to be divided—as history used to be—into ‘periods’, the years of Saint Augustine's episcopate would mark an important watershed among them. Little more than twenty years lie between the publication of the last great work of classical historiography, that of Ammianus Marcellinus, and the Seven books of histories against the pagans by Orosius. In 395, when Ammianus, in all probability, had just completed his work, Augustine became bishop of Hippo. Orosius, the Spanish priest who had found his way to Hippo in his flight from the barbarian upheavals in his home province, wrote his work at Augustine's bidding, in the years 416–17. Ten books of his master's great work of historical apologetics, the City of God, were by now completed. Ammianus was not much read during the middle ages; Orosius, though he found few imitators, became one of the standard text-books. To contrast these two authors as ‘classical’ and ‘medieval’ or as ‘pagan’ and ‘Christian’ does not take us far. They share scarcely any assumptions about how history is to be written and what it is about. Ammianus wrote towards the end of a century of profound changes in the life of the Roman Empire, political, economic and social, as well as religious. The rate of change quickened towards the end of the century. A further crisis lay between the publication of his book and the writing of Orosius's. These were the years following the death of Theodosius I, the years which saw the division of the Empire between his young sons and the political troubles attendant on the eclipse of imperial power.