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.
Emperor Constantine.
The Roman provinces were the administrative regions of Ancient Rome outside Roman Italy that were controlled by the Romans under the Roman Republic and later the Roman Empire. Each province was ruled by a Roman appointed as governor.
Roman Empire under Augustus (31 BC – AD 14), showing the empire as of 31 BC in yellow, additions to 19 BC in dark green, additions in 9 BC in light green, and additions to AD 6 in pale green. Client states in mauve.