The era of Diocletian and Constantine is a significant period for the Roman empire, with far-reaching administrative changes that established the structure of government for three hundred years, and the time when the Christian Church passed from persecution to imperial favour. It is also a complex period of co-operation and rivalry between a number of co-emperors, the result of Diocletian's experiment of government by four rulers (the tetrarchs).

This book examines imperial government at this crucial but often neglected period of transition, through a wide study of the pronouncements that the emperors and their officials produced, drawing together material from a wide variety of sources: the law codes, Christian authors, inscriptions, and papyri. The study covers the format, composition, and promulgation of documents, and includes chronological catalogues of imperial letters and edicts, as well as extended discussions of the Gregorian and Hermogenian Codes, and the ambitious Prices Edict. Much of this has had little detailed coverage in English before. There is also a chapter that elucidates the relative powers of the members of the imperial college.

Finally, Dr Corcoran assesses how effectively the machinery of government really matched the ambitions of the emperors.