Ammianus’ account of the reign of the emperor Jovian (27 June 363-17 February 364) provides an excellent case study of Ammianus’ authorial technique. It is itself relatively brief (the last six chapters of Book 25), and focuses strongly on two main subjects: the new emperor’s election, and the peace treaty which he subsequently negotiated with the Persians. The reign also receives coverage in a variety of other sources, not least Themistius’ fifth Oration. The latter provided the starting-point for this chapter,1 and also suggests a third subject for consideration here: Jovian’s religious policies. The range of alternative sources makes it possible to consider not just what Ammianus actually wrote, but also what he might have written, and hence bring into focus the way in which his skills as a writer were deployed to shape the available raw material.2