This is the final volume in the series of commentaries on Ammianus’ Res Gestae. The last book of Ammianus Marcellinus’ Res Gestae is the most important source for a momentous event in European history: the invasion of the Goths across the Danube border into the Roman Empire and the ensuing battle of Adrianople (378 CE), in which a Roman army was annihilated and the emperor Valens lost his life. Many contemporaries were of the opinion that this defeat heralded the decline of the Empire. Ammianus is sharply critical of the way Valens and his generals handled the military situation, but holds on to his belief in the permanence of Roma Aeterna, reminding his readers of earlier crises from which the Empire had recovered and pointing to the incompetence of the barbarians in siege craft.