This is a commentary on Book XXIV of the Res Gestae by the fourth century historian Ammianus Marcellinus. The commentary discusses philological, literary, linguistic and historical problems in the Latin text.

This is the first book on Ammianus to place equal emphasis on the literary and historical aspects of his writing. Barnes assesses Ammianus' depiction of historical reality by simultaneously investigating both the historical accuracy and the literary qualities of the Res Gestae. He examines its structure and arrangement, emphasizes its Greek, pagan, and polemical features, and points out the extent to which Ammianus drew on his imagination in shaping the narrative.

Book 26 of Ammianus' Res Gestae is the first of the hexad which deals with the rule of the emperors Valentinian and Valens (364-378). In the first five chapters Ammianus describes the election of Valentinian, who appointed his brother Valens as his co-ruler, and subsequently divided the empire into an eastern and a western part. The next chapters deal with the revolt of Procopius. They offer the most detailed account of a coup d' état in Roman historiography. The memory of Julian, whose death was the central theme of the preceding book, is still very much alive. None of the three protagonists of Book 26 was remotely his equal. His loss meant a turn for the worse in the history of Rome.

In Book 28 Ammianus describes the military activity of Valentinian on the Rhine. The historian speaks with admiration about his efforts to strengthen the northwestern border of the empire. He shows a similar esteem for the general Theodosius, who re-established order in Britain. However, in the greater part of Book 28 there is an air of gloom. Ammianus writes reluctantly about the judicial terror inflicted on the Roman aristocracy by powerful magistrates. In his digression about Roman manners he speaks with contempt about the senatorial elite and the Roman plebs, because they fail to live up to the standards of their ancestors. The final chapter illustrates the disastrous effects of the mismanagement of the province of Tripolis by corrupt officials.

Book 29 opens with the judicial terror in Antioch following the discovery of a plot against the emperor in the East, Valens, who played an active role in hunting down and executing the culprits. The account of these internal troubles is balanced by two long chapters at the end of the book dealing with warfare in Africa and Central Europe. The general Theodosius mercilessly crushed the revolt of the Moorish prince Firmus, while the emperor in the West, Valentinian, had to deal with violent invasions of the Quadi and the Sarmatians. The two central chapters are devoted to different aspects of Valentinian’s character, his cruelty on the one hand, his diligence in reinforcing the border defenses on the other.

Continuing the series of philological and historical commentaries on Ammianus' Res Gestae this volume deals with Book 28, which is devoted primarily to the deplorable events in Rome during the reign of Valentinian and his defense of the Rhine frontier.