Praetorian prefect was the title of a high office in the Roman Empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

. Originating as the commander of the Praetorian Guard

Praetorian Guard

The Praetorian Guard was a force of bodyguards used by Roman Emperors. The title was already used during the Roman Republic for the guards of Roman generals, at least since the rise to prominence of the Scipio family around 275 BC...

, the office gradually acquired extensive legal and administrative functions, with its holders becoming the Emperor's chief aides. Under Constantine I

Constantine I

Constantine the Great , also known as Constantine I or Saint Constantine, was Roman Emperor from 306 to 337. Well known for being the first Roman emperor to convert to Christianity, Constantine and co-Emperor Licinius issued the Edict of Milan in 313, which proclaimed religious tolerance of all...

, the office was much reduced in power and transformed into a purely civilian administrative post, while under his successors, territorially-defined praetorian prefecture

Praetorian prefecture

The praetorian prefecture was the largest administrative division of the late Roman Empire, above the mid-level dioceses and the low-level provinces. Praetorian prefectures originated in the reign of Constantine I The praetorian prefecture was the largest administrative division of the late Roman...

s emerged as the highest-level administrative division of the Empire.