VICARIUS. - Title of an official of the Roman Empire. At first an extraordinary representative of the praefectus praetorio, under Diocletian he assumed the form of an autonomous office.
He was placed at the head of the large districts (dioceses) which, numbering twelve at first and later fifteen, grouped together the provinces, and whose union gave rise to the four prefectures into which—beginning with the age of Constantine—the whole Empire was divided.
Appointed directly by the emperor, the v., although hierarchically subordinate to the praefectus praetorio, not only possessed his own administrative and jurisdictional authority, but also constituted a body supervising the activity of the praefectus himself. He was furthermore entrusted with the oversight of the governors of the provinces composing his diocese and could impose fines upon them. The V. was entitled to the honorary appellation spectabilis.