The so-called Chronica urbis Romae has long been valued for the exact year-month-day figures that it gives for the reign of every Roman emperor from Julius Caesar to Licinius, especially those for the emperors of the third century, whose dates of accession and death are for the most part unknown. This book, for the first time, submits every year-month-day figure found in this text to a detailed historiographical analysis that puts our understanding of the historical accounts of the chronologies of the Roman emperors - particularly those of the third century - on a completely new footing. In so doing it provides new insights into the nature of this text and the methods of Roman historians. This volume concludes with detailed studies of the chronological information on Roman emperors provided by Cassius Dio and the witnesses to the now-lost fourth-century Kaisergeschichte; a new critical edition and translation of the text based upon a fresh examination of all the manuscripts and made in the light of recent studies; and an analysis of the verbal parallels between this text and other surviving Greek and Latin histories, particularly those of the fourth century.