The era of Diocletian and Constantine—when the Christian church passed from persecution to imperial favor—saw far-reaching administrative changes that established the structure of government in the Roman Empire for three hundred years. This was a complex period of cooperation and rivalry between co-emperors, the result of Diocletian's experiment in government by four rulers, the tetrarchs. Drawing together material from a wide variety of sources, Corcoran studies the vast range of documents issued by the emperors and their officials, and assesses how effectively the machinery of government matched imperial ambitions.