Constantine the Great died on 22 May ad 337. He left behind three sons, Constantine II, Constantius II, and Constans, to face the challenge of how to rule the Roman empire, and how to divide it between them. This book follows the lives of the sons from the death of their father and traces how they first shared the empire as a triarchy, until Constantine II was killed by his brother Constans in the civil war of 340, and after that as a diarchy, until Constans was murdered by a usurper in 350. It also tackles the question of division. It is well known that the Roman empire came to be divided into eastern and western halves in 395; what is less known is that this was the culmination of a great series of divisions and reunifications stretching across the fourth century. Division was a process, rather than an event, and it is a process that has received little attention in scholarship. This book uses the power-sharing of the sons of Constantine as a case study for division, and how it worked in practice. Constantius was the last man standing of Constantine’s sons, and reunified the empire under the rule of a sole Augustus, like his father. However, the cracks were already starting to show. The reunification of the empire proved to be a failure, and this book traces the threads of Constantinian division as the empire ossified into separate halves.