Praetorian prefect (, ) was the title of a high office in the
Roman Empire. Originating as the commander of the
Praetorian Guard, the office gradually acquired extensive legal and administrative functions, with its holders becoming the Emperor's chief aides. Under
Constantine I, the office was much reduced in power and transformed into a purely civilian administrative post, while under his successors, territorially-defined
praetorian prefectures emerged as the highest-level administrative division of the Empire. The prefects again functioned as the chief ministers of the state, with many laws addressed to them by name. In this role, praetorian prefects continued to be appointed until the reign of
Heraclius in the 7th century CE, when wide-ranging reforms reduced its power and converted it to a mere overseer of provincial administration. The last traces of the prefecture disappeared in the
Byzantine Empire by the 840s.