An exarch was the holder of any of various historical offices, some of them being political or military and others being ecclesiastical.

In the Late Roman Empire, usually dated 284 AD to 641 AD, the regional governance district known as the Roman or civil diocese was made up of a grouping of provinces each headed by a Vicarius, who were the representatives of praetorian prefects. There were initially twelve dioceses, rising to fourteen by the end of the 4th century.