VICARIUS. — Title of an official in the Roman Empire. Initially the extraordinary representative of the praefectus praetorio, under Diocletian it assumed the character of an autonomous organ.
He was placed at the head of the great administrative districts (dioceses), which, initially numbering twelve and later fifteen, grouped the provinces and whose union gave rise to the four prefectures into which—from the time of Constantine onward—the entire Empire was divided.
Appointed directly by the emperor, the vicarius, although hierarchically inferior to the praefectus praetorio, not only possessed his own administrative and judicial power but also served as a controlling organ over the activities of the praefectus himself. He was also responsible for overseeing the governors of the provinces within his diocese and could impose fines upon them. The vicarius bore the honorary title of spectabilis.