The Praetorian Guard (Latin: cohortēs praetōriae) was an elite unit of the Imperial Roman army that served as personal bodyguards and intelligence agents for the Roman emperors.
During the Roman Republic, the Praetorian Guards were escorts for high-ranking political officials (senators and procurators) and were bodyguards for the senior officers of the Roman legions. In 27 BC, after Rome's transition from republic to empire, the first emperor of Rome, Augustus, designated the Praetorians as his personal security escort. For three centuries, the guards of the Roman emperor were also known for their palace intrigues, by whose influence upon imperial politics the Praetorians could overthrow an emperor and then proclaim his successor as the new caesar of Rome. In AD 312, Constantine the Great disbanded the cohortes praetoriae and destroyed their barracks at the Castra Praetoria.
In the period of the Roman Republic (509–27 BC) the Praetorian Guard originated as bodyguards for Roman generals. The first historical record of the praetorians is as bodyguards for the Scipio family, ca. 275 BC. Generals with imperium (command authority of an army) also held public office, either as a magistrate or as a promagistrate, each was provided with lictors to protect the person of the office-holder. In practice, the offices of Roman consul and of proconsul each had twelve lictors, whilst the offices of praetor and of propraetor each had six lictors. In absence of an assigned, permanent personal bodyguard, senior field officers safeguarded themselves with temporary bodyguard units of selected soldiers. In Hispania Citerior, during the Siege of Numantia (134–133 BC), General Scipio Aemilianus safeguarded himself with a troop of 500 soldiers against the sorties of siege warfare aimed at killing Roman field commanders.
At the end of 40 BC, two of the three co-rulers who were the Second Triumvirate, Octavian and Mark Antony, had Praetorian Guards. Octavian installed his praetorians within the pomerium, the religious and legal boundary of Rome; the first occasion when troops were permanently garrisoned in Rome proper.