A praetorian prefecture was the largest civil region of the late Roman Empire. Each was run by a praetorian prefect, who began as commander of the emperor's guard. By about AD 400 there were four, grouping the dioceses of the empire.
Key takeaways
- Praetorian prefects began as the two commanders of the Praetorian Guard, then became the emperor's chief administrators [1].
- Around AD 400 there were four prefectures: Gaul, Italy, Illyricum and the East [1].
- The map draws 43 provinces from about AD 200, not prefectures, which came much later.
- Each prefecture contained several dioceses, and each diocese contained several provinces [1].
How praetorian prefectures worked
The Praetorian Guard was the emperor's household force, and it was led by two praetorian prefects. Over time the prefects became the emperor's chief aides, with wide administrative and judicial duties [1]. Historians are not sure exactly how they turned into civil administrators of whole regions. A popular claim that Constantine created territorial prefectures in AD 318 or 324 comes from a late writer, but Wikipedia's article treats it as a misconception [1].
What seems clear is the sequence. Under the tetrarchy, there were two prefects at any time, probably one for each senior emperor. After Constantine reunited the empire, the prefect's military duties passed to new army commanders, and the office became purely civilian. When Constantine died in AD 337 his sons divided the empire and each new Augustus had his own prefect, which created the first permanent territorial prefectures [1].
By about AD 400, as recorded in an official list called the Notitia Dignitatum, there were four [1]:
- Gaul: the dioceses of Gaul, Viennensis, Hispania and Britain.
- Italy: the dioceses of Italy, Africa, Pannonia, Dacia and Macedonia.
- Illyricum: sometimes a separate prefecture, covering Pannonia, Dacia and Macedonia.
- The East: the dioceses of Thrace, Asia, Pontus and Oriens.
The prefecture was the biggest unit in the civil system. Each contained several dioceses, and each diocese contained provinces [1]. The dioceses were headed by vicars who answered to the prefect [2].
What the map does and does not show
The map does not draw prefectures. Its province layer shows 43 outlines based on the empire around AD 200, long before these regions existed. From AD 395 the map colours the East purple and the West orange, which is a political split between two emperors, not a map of the prefectures. Readers should not mix up the two.
An example from our data
Look at the year of the split, AD 395, where the map's event is "Theodosius I dies; the empire is divided permanently between his sons". The map counts 42 provinces held and an area of 4.72 million km². Behind that single picture sat the late Roman system of prefectures, which the map itself does not draw.
Earlier, the picture was different. In AD 211 the map counts 43 provinces held and an area of 4.81 million km², and nothing like a prefecture existed yet. Compare the two year pages to see how much the system changed. The homepage section on East and West explains the split between the two halves, and the Byzantine Empire page follows the Eastern half after the West fell.
The thing people get wrong
The name sounds as if a praetorian prefecture was a military district run by the guard. By the time territorial prefectures appeared, the office was civil: the prefect's military duties had gone to other commanders [1]. The title is a leftover from the guard where it began.
A second mistake is to think the four prefectures were the same thing as the Eastern and Western halves. They were civil regions of a different kind, and the split into two halves was a political arrangement between emperors.
Frequently asked questions
Who were the praetorian prefects?
They started as the two commanders of the emperor's bodyguard, the Praetorian Guard. They later became the emperor's chief aides, and finally civil governors of large regions.
How many praetorian prefectures were there?
Four by about AD 400: Gaul, Italy, Illyricum and the East. At times Illyricum was separate and at times it was not.
Are prefectures on the map?
No. The map draws the provinces of about AD 200, and a different colour for the Eastern and Western halves after AD 395.
Sources
- Praetorian prefecture, Wikipedia.
- Roman diocese, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against Ancient World Mapping Center outlines and Pleiades).