Under the Dominate, "i.e." the Late Roman Empire, the emperor Diocletian began in AD 293 reforms of the provincial administration that were completed under the Emperor Constantine the Great in 318. Diocletian set up 12 dioceses (later several were split; see under Roman province), originally two to four for each of the four co-emperors under the short-lived Tetrarchy (two senior "Augusti", each above a "Caesar"), each governed by a "vicarius" ('vicar') who acted on behalf of the praetorian prefect. Each diocese comprised several Roman provinces (known in Greek as "eparchies"), each under the authority of a provincial governor, whose title varied from province to province (the range of titles includes republican relics such as "proconsul," as well as novelties such as "corrector provinciae", "moderator provinciae", and "praeses provinciae"). Although the vicar's authority was supreme within his diocese, he was under the authority of praetorian prefect whose power he partook of (see below) or the emperor himself.