Origins
The Praetorian Guard evolved from the personal bodyguards that Roman generals had employed since the Republic. The term “praetorian” derived from praetorium, the general’s tent in a military camp, and cohors praetoria originally referred to the elite troops protecting the commander. Julius Caesar, Pompey, and Marc Antony all maintained such guards during the civil wars of the late Republic. When Augustus (formerly Octavian) emerged victorious and established the Principate in 27 BCE, he formalized this institution into a permanent imperial guard stationed in and around Rome.
Augustus initially established nine praetorian cohorts, each of approximately 500 men, though he kept only three in Rome while dispersing the others in nearby Italian towns to avoid the appearance of military occupation. This was a politically astute compromise: the emperor needed protection in a city where weapons were traditionally forbidden, but Romans were deeply suspicious of standing armies within the sacred boundary (pomerium) of the city. Under Tiberius’s prefect Sejanus, all nine cohorts were concentrated in a single fortified camp, the Castra Praetoria, on Rome’s northeastern edge—a fateful centralization that magnified the Guard’s political influence.
The Praetorians enjoyed significant advantages over regular legionaries. They served only sixteen years (versus twenty in the legions), received triple pay, and were stationed in the empire’s capital rather than distant frontiers. Recruitment initially drew from Italy and heavily Romanized provinces, though this gradually expanded. The Guard attracted ambitious soldiers seeking proximity to power, comfortable postings, and rapid advancement. Their privileged position, however, contained the seeds of political dysfunction: soldiers with such power over the emperor’s person inevitably recognized their ability to influence imperial succession.
Structure & Function
The Praetorian Guard was organized into cohorts (cohortes praetoriae), varying in number from nine under Augustus to sixteen under Vitellius, before stabilizing at ten under Vespasian. Each cohort was commanded by a tribune, with centurions leading individual centuries. At the Guard’s head stood the Praetorian Prefect (praefectus praetorio), one of the most powerful positions in the empire. The Prefect commanded the Guard, administered military justice in Italy, and gradually accumulated judicial, administrative, and advisory functions that made the office second only to the emperor himself.
The Guard performed multiple functions beyond personal protection. Praetorians accompanied the emperor everywhere, maintained order at public events, arrested enemies of the state, conducted sensitive political operations, and served as a rapid reaction force. In wartime, they fought alongside the legions, often forming the elite reserve that decided critical battles. Their ceremonial duties at court, games, and state occasions kept them visible as symbols of imperial power. The fire brigades (vigiles) and urban cohorts (cohortes urbanae) served under related commands, creating a comprehensive security apparatus for Rome.
Politically, the Guard’s relationship with each emperor followed a transactional logic. New emperors traditionally secured Praetorian loyalty through donatives—massive cash payments distributed upon accession. Claudius reportedly paid 15,000 sesterces per man (equivalent to over ten years’ pay for a legionary) to the Praetorians who had proclaimed him emperor after assassinating Caligula. This established a dangerous precedent: the Guard came to expect increasingly large payments for their support, and emperors who could not or would not pay faced deadly consequences.
Historical Significance
The Praetorian Guard embodied what modern scholars call the “Praetorian problem”—the tendency of elite military units to become political actors rather than servants of the state. Over their three-century existence, the Praetorians were implicated in the deaths of at least thirteen emperors and the proclamation of numerous others. Their intervention in succession crises demonstrates how personal loyalty to a leader can become institutional self-interest: by the third century, the Guard openly auctioned the throne to the highest bidder (famously selling it to Didius Julianus in 193 CE).
The Guard’s influence extended beyond coups and assassinations. Praetorian Prefects became the emperors’ most trusted advisors and administrators, with some—like Sejanus under Tiberius—effectively running the empire. The office evolved into a supreme judicial and administrative position; second-century prefects like Papinian and Ulpian were among Rome’s most distinguished jurists. This dual military-administrative role influenced later institutions, including the Byzantine tagmata and Ottoman household troops.
Constantine I’s dissolution of the Praetorian Guard in 312 CE, after their support for his rival Maxentius, ended the institution but not the problem it represented. Throughout history, elite guards have repeatedly followed the Praetorian pattern: the Janissaries, the Streltsy, and various palace guards have all transformed from protectors to political kingmakers. The term “Praetorian” itself became a byword for military intervention in politics, and the “Praetorian problem” remains a central concern in civil-military relations theory, particularly regarding developing nations where military coups threaten democratic governance.
Key Developments
- 27 BCE: Augustus establishes nine praetorian cohorts as permanent imperial guard
- 2 BCE: Augustus appoints first Praetorian Prefects (two, to prevent concentration of power)
- 23 CE: Sejanus concentrates all cohorts in Castra Praetoria; Guard’s political influence increases
- 31 CE: Sejanus, having dominated Tiberius’s government, is overthrown and executed
- 41 CE: Praetorians assassinate Caligula; proclaim Claudius emperor and receive massive donative
- 68-69 CE: Year of Four Emperors; Praetorians switch allegiances multiple times
- 69 CE: Vespasian reorganizes Guard at ten cohorts; reforms recruitment
- 193 CE: Guard murders Pertinax, auctions throne to Didius Julianus
- 193 CE: Septimius Severus disbands existing Guard, reconstitutes with loyal legionaries
- 217 CE: Praetorian Prefect Macrinus orchestrates Caracalla’s assassination, becomes emperor
- 238 CE: Praetorians murder Balbinus and Pupienus after brief reign
- 284 CE: Praetorians proclaim Diocletian; Guard’s influence wanes as emperors leave Rome
- 306-312 CE: Guard supports Maxentius in civil war against Constantine
- 312 CE: Constantine defeats Maxentius at Milvian Bridge; disbands Praetorian Guard permanently