prefect, in ancient Rome, any of various high officials or magistrates having different functions.
In the early republic, a prefect of the city (praefectus urbi) was appointed by the consuls to act in the consuls’ absence from Rome. The position lost much of its importance temporarily after the mid-4th century bc, when the consuls began to appoint praetors to act in the consuls’ absence. The office of prefect was given new life by the emperor Augustus and continued in existence until late in the empire. Augustus appointed a prefect of the city, two praetorian prefects (praefectus praetorio), a prefect of the fire brigade, and a prefect of the grain supply. The prefect of the city was responsible for maintaining law and order within Rome and acquired full criminal jurisdiction in the region within 100 miles (160 km) of the city. Under the later empire he was in charge of Rome’s entire city government. Two praetorian prefects were appointed by Augustus in 2 bc to command the praetorian guard; the post was thereafter usually confined to a single person. The praetorian prefect, being responsible for the emperor’s safety, rapidly acquired great power. Many became virtual prime ministers to the emperor, Sejanus being the prime example of this. Two others, Macrinus and Philip the Arabian, seized the throne for themselves.
By ad 300 the praetorian prefects virtually directed the civil administration of the empire. They executed judicial powers as delegates of the emperor, organized tax levies, and supervised provincial governors. They also commanded troops and served as quartermasters general to the emperor’s court. Under the emperor Constantine I the Great (reigned 312–337), the praetorian prefects were stripped of their military commands, but they retained their judicial and financial functions and remained the highest officers of the empire.