This book explores the reign of Constantine the Great (306-337) and, more generally, the political history of the third century, thus putting Constantine's career and many of his decisions in context. It traces events under the first Tetrarchy and then explores Constantine's rise to power, his rule and reforms, and continuity and change with regard to his predecessors. It considers how he was able to transform the empire and establish his own dynasty, highlighting his political and military prowess, and therefore provides an essential overview of the political history of the period.