In Books 26 ?31 Ammianus Marcellinus deals with the period of the emperors Valentinian and Valens. The representatives of the new dynasty differ greatly from their predecessor Julian, both personally and in their style of government. The Empire is divided between the two rulers, and suffers increasingly from barbarian invasions. Faced with these changes, Ammianus adapts his historical method. His treatment of the events becomes less detailed and more critical. The years following on the death of Julian are painted in dark colours, as the disaster at Hadrianople casts its shadow before. The papers in this volume, on History and Historiography, Literary Composition and Crisis of Empire, were presented during the conference \'Ammianus after Julian\' held in 2005.