1. They originated during the Roman Republic.

Relief showing Praetorian Guard

The Praetorian Guard was a fixture of the imperial era, but their origins date back to groups of elite soldiers that protected generals during the Roman Republic. As early as the second century B.C., special units were selected to shadow famed Roman leaders such as Marc Antony, Scipio Africanus and Lucius Cornelius Sulla whenever they ventured into the field. Julius Caesar later enlisted his tenth legion as personal security, but the Praetorian Guard as we know it didn’t appear until shortly after Augustus became Rome’s first emperor in 27 B.C. After ascending to the throne, Augustus established his own imperial guards comprised of nine cohorts of 500 to 1,000 men each. The unit would endure as a symbol of imperial might for over 300 years. By A.D. 23, it even operated out of its own fortress, the Castra Praetoria, located on the outskirts of Rome.

2. They served as emergency firefighters.

Fire was a constant threat in ancient Rome, and though the Empire had had a dedicated firefighting corps called the “Vigiles,” it wasn’t unusual for the emperor’s Praetorians to lend a hand in the event of a particularly unruly blaze. Guardsmen are known to have chipped in at a fire at the Temple of Vesta, and they were likely involved in setting up firebreaks during an infamous conflagration that leveled much of Rome during Nero’s reign. While the Praetorians significant numbers would have helped combat fires, their presence also had a public relations component. By dispatching his personal guard to assist in disaster relief, the emperor could show the citizenry that he was concerned for their welfare.

3. They performed at the Roman games.

The Praetorian Guard often handled crowd control at the Roman games, but they occasionally stepped into the arena and played an active role in the bloodshed. There is evidence that the Guard took part in gruesome wild beast hunts to demonstrate their combat prowess, and they played a notorious role in a “naumachia,” or staged sea battle, hosted by Emperor Claudius in A.D. 52. The spectacle saw as many as 19,000 men and some 100 boats clash in a mock naval engagement on the Fucine Lake. Most of the participants were prisoners and slaves, and the Praetorians, armed with catapults and ballistae, surrounded the battle on rafts to add to the mayhem and prevent any of the condemned from escaping.

4. They acted as a secret police force.

Credit: Hulton Archive/Getty Images

The Praetorians were known to engage in espionage, intimidation, arrests and killings to protect the interests of the Roman emperor. For clandestine operations, they may have employed a special wing of troops known as “speculatores.” Formerly a reconnaissance corps under the Roman Republic, by the imperial era this unit had graduated to serving as couriers and intelligence operatives in the service of the Caesar. Speculatores and other members of the Praetorians would disguise themselves as ordinary citizens at gladiator contests, theatrical performances and protests to monitor and arrest anyone who criticized the emperor. They also kept tabs on suspected enemies of the state, and in some cases they even secretly executed those judged to be an imminent threat to the emperor or his policies.

5. They played a role in assassinating several emperors.

Praetorian Guard proclaiming Claudius emperor

The Praetorians’ may have been tasked with protecting the Roman Emperor, but they were also the single greatest threat to his life. The unit was a major player in the webs of deceit that characterized imperial Rome, and they were willing to slaughter and install new emperors when tempted by promises of money or power. Disgruntled Praetorians famously engineered the assassination of Caligula and the selection of Claudius as his successor in A.D. 41. Among others, the Guard or their prefect also played a part in the murder of Commodus in 192, Caracalla in 217, Elagabalus in 222 and Pupienus and Balbinus in 238. In some cases, the Praetorians were partially responsible for both installing andmurdering a would-be emperor. Galba ascended the throne in A.D. 68 after winning the support of the Guard, only to be killed at their hands the following year after he neglected to properly reward them. Likewise, Emperor Pertinax was confirmed by the Praetorians in 193 and then slain just three months later when he tried to force them to accept new disciplinary measures.

6. They famously auctioned the emperorship to the highest bidder.

Didius Julianus (Credit: Anderson Alinari/Getty Images)

According to the ancient historian Cassius Dio, after murdering Emperor Pertinax in A.D. 193, the Praetorian Guard tried to cash in on the power vacuum by placing the Roman throne on the auction block. Following a brief bidding war between former consul Didius Julianus and Pertinax’s father-in-law, Titus Flavius Sulpicianus, the Praetorians reportedly sold control of the Empire to Julianus for the enormous sum of 25,000 Roman sesterces per man. The incident is one of the most notorious episodes in the unit’s history, but some historians argue that Dio’s account of an imperial “auction house” is overblown. While Julianus paid the Praetorians a fortune for their support, the Guard was equally motivated by fear that Sulpicianus would seek revenge for the killing of his son-in-law after ascending the throne.

7. They once fought against one another in battle.

Vespasian crowned emperor (Credit: DeAgostini/Getty Images)

One of the most unusual incidents in the Praetorians’ history came in A.D. 69, when the general Vitellius defeated the Emperor Otho and seized the Roman throne. Fearing assassination at the hands of Otho’s loyal Praetorians, Vitellius dismissed the standing members of the Guard and replaced them with a new, larger force of troops recruited from his own legions. Unfortunately for Vitellius, his reign lasted mere days before Vespasian, the commander of the legions in Judea, declared himself emperor and moved on Rome. Vespasian enlisted several of the Otho’s now-unemployed Praetorians in his army, and these aggrieved soldiers later clashed with Vitellius’ Guard in a series of heated battles on the outskirts of the city. Vespasian ultimately prevailed, and the exiled Praetorians were restored to their former positions.

8. They were disbanded for supporting a pretender to the Roman throne.

Battle of the Milvian Bridge

The structure of the Praetorian Guard was permanently altered in the late-second century, when the Emperor Septimius Severus dismissed its members and began recruiting bodyguards directly from the legions. Still, their run as the guardians of the Roman throne didn’t officially end until the fourth century. In 306, the Praetorians tried to play the role of kingmaker one last time when they installed the usurper Maxentius as the western emperor in Rome. Following a dizzying chain of civil wars and rival claims to the throne, Maxentius and his Praetorians were confronted by the Emperor Constantine at 312’s Battle of Milvian Bridge. While the Praetorians supposedly made a valiant last stand along the Tiber River, they were soundly defeated, and Maxentius was killed. Convinced the Praetorians could no longer be trusted, Constantine disbanded the unit once and for all, reassigned its members to the outskirts of the Empire, and oversaw the destruction of their barracks at the Castra Praetoria.