The Praetorian Guard: the real power behind the Roman emperors

At first, Roman generals typically created small protective units made up of their most loyal soldiers.

Scipio Africanus and Julius Caesar each formed personal bodyguards from among their veterans.

These units generally existed outside formal army command and served as close protection during campaigns. 

Augustus gave this informal tradition official organisation after he had taken sole control in 27 BCE and, by 13 BCE, he had established twelve cohorts under central leadership, stationed across Italian cities.

Tiberius later reduced their number to nine to limit their size and concentrate control.

Each cohort consisted of around 500 men who pledged their loyalty directly to the emperor, bypassing Senate oversight and regular army channels.

The first Praetorian Prefects are absent from early records with later figures such as Lucius Seius Strabo and his son Sejanus appearing in the records. 

Initially, Augustus avoided placing all twelve cohorts in the city to prevent unrest or accusations of tyranny, but over time, that caution faded.

In 23 CE, Tiberius relocated the Guard into a permanent base within Rome called the Castra Praetoria.

Built just outside the Servian Wall, the rectangular fort measured about 440 by 380 metres and placed the Guard close to the emperor's decisions, palace movements and the Senate's sessions.

Entry into the Guard depended on a combination of proven service and personal recommendation.

Most recruits came from central Italian regions such as Etruria, Umbria, and Latium, which emperors trusted for their cultural loyalty and familiarity with Roman norms.

Preference was often given to those who had notable service records from previous military roles. 

Unlike legionaries who typically served for twenty years, Praetorians completed their term of service in sixteen years.

This shorter commitment made the position attractive, along with better pay and earlier retirement.

Under Augustus, ordinary legionaries received a base annual salary of around 900 sesterces, later raised to 1,200 by Domitian, while the Praetorians under Augustus likely earned between 1,500 and 1,800 sesterces annually, but this rose to as much as 3,000 under later emperors.

At retirement, they earned donativa, which were lump sum payments or land grants, and these often allowed them to enter local society or join local politics. 

Praetorians often moved quickly into higher positions, some of whom frequently became centurions or optiones after only a few years.

The highest authority within the Guard was the Praetorian Prefect, who typically managed all nine cohorts, managed internal discipline, and served as the emperor’s personal advisor.

Over time, this role expanded into legal and administrative powers as well. Some Prefects, such as Macrinus in the early third century, even rose to the imperial throne. 

Under Augustus, their pay reached levels far beyond those of any other soldiers.

Later emperors sometimes added bonuses to maintain their support during transitions or crises.

Their legal protection also set them apart, as Guards operated within the city without control by provincial governors or military tribunals.

They arrested senators, executed rivals, and enforced imperial decrees without challenge.

Very few civilian authorities could effectively restrain them once they received orders from the emperor or Praetorian Prefect.

Notably, during the reigns of Domitian and Elagabalus, they assisted in the targeted removal of imperial enemies. 

Additionally, during public festivals and triumphs, the Guard marched in formation beside the emperor, and often stood at his side during Senate visits, or surrounded him during games, to remain visible reminders of armed authority inside Rome.

Their presence showed imperial strength and discouraged opposition. 

Once stationed within the city, the Guard secured access to private meetings and to the decrees and plans that governed imperial succession.

They listened at doors, escorted ambassadors, and carried messages between imperial relatives and, over time, they developed a growing awareness of factions and rivalries within the palace, which allowed them to exploit tension for their benefit. 

Some emperors who lacked popular support came to rely increasingly on the Guard as their only protection.

They frequently paid higher donatives or granted political favours to maintain that loyalty, which led the Guard to begin demanding influence in appointments and in trials and decisions over inheritances. 

For instance, emperors who delayed payments often faced mutiny or assassination, while others who relied on different forces, such as provincial legions, soon discovered that the Guard would not tolerate rivals.

Those realities made emperors increasingly cautious, but also increasingly vulnerable.

Following the death of Augustus, the succession of Tiberius introduced the Guard to political intrigue on a new scale.

While Tiberius gradually secured support, the real shift occurred when Lucius Aelius Sejanus, who was his Praetorian Prefect, began eliminating rivals. 

By 23 CE, Sejanus had convinced Tiberius to centralise the Guard in Rome and give him sole command. He then positioned himself to control access to the emperor, directing correspondence and managing important political appointments.

Once Tiberius had withdrawn to Capri in 26 CE, Sejanus effectively governed the city alone. 

At first, the Senate obeyed him out of fear, but later, they began to see his drive for power.

In 31 CE, Tiberius issued a sudden order for his arrest, delivered during a Senate meeting. Sejanus was executed the same day.

His downfall revealed both the Guard's willingness to act and the danger of allowing a single commander too much authority.

In 41 CE, the assassination of Caligula by disgruntled Praetorians shocked the Senate.

Caligula had repeatedly mocked and insulted his bodyguards, often treating them as servants rather than soldiers.

However, his murder created a vacuum, and some senators considered alternatives to the imperial system. 

However, the Guard acted swiftly: they found Claudius, who was Caligula’s uncle, hiding in a corner of the palace and declared him emperor.

They then escorted him to the Castra Praetoria, where he accepted their acclamation.

To secure their support, Claudius paid a donative of 15,000 sesterces to each soldier, which was an unprecedented bribe. 

This event made clear that the Senate had lost control of imperial succession.

From that point forward, the Praetorian Guard assumed the right to confirm or deny any new emperor. 

Later, after Nero’s death in 68 CE, chaos erupted. Galba took power with support from the Senate but refused to honour the Guard’s expectation of a donative, which proved to be a fatal decision.

Within months, they turned against him and backed Otho, who had promised payment and favours. 

Vitellius, supported by the legions of Germania, then marched on Rome and defeated Otho’s forces.

However, the Guard remained a threat to his authority. As Vespasian’s troops approached from the east, elements within the Guard quietly opened the city’s gates.

Once Vespasian had taken control, he dismissed much of the Guard and rebuilt it with men from his own Danubian legions.

While some ancient accounts suggest Vitellius expanded the Guard to sixteen cohorts, the exact number remains uncertain.

Regardless, Vespasian reduced them back to nine. 

Each transition during 69 CE showed that the Guard held the power to preserve or destroy emperors.

Their allegiance did not rest on law or tradition, but depended on personal benefit. 

In 193 CE, the death of Pertinax exposed the Guard’s full corruption in full. After they had killed the emperor during a dispute over military discipline, the Praetorians shut themselves inside their barracks and said that the imperial throne was for sale. 

Two senators named Sulpicianus and Didius Julianus submitted competing offers.

Julianus outbid his rival by promising 25,000 sesterces per soldier, so the Guard accepted his offer and declared him emperor on the spot.

The Senate, under threat, confirmed the appointment. 

However, outrage spread quickly and the legions in the provinces, which were disgusted by the sale of imperial power, declared support for Septimius Severus.

As Severus approached the capital, Julianus failed to mount a defence. The Senate condemned him to death, and Severus removed many members from the Guard, replacing it with his own men drawn from loyal Pannonian legions. 

Afterward, few viewed the Guard as honourable or loyal. Their role in selling the empire became the darkest chapter in their history.

Following Severus’ reforms, the Guard never fully regained its former position.

Later emperors bypassed the Guard by creating alternate protective units that included the equites singulares or personal cavalry escorts.

They had substantially reduced the Guard's numbers and had shifted reliance to provincial troops, which undermined its influence. 

Eventually, Constantine the Great delivered the final blow after he had defeated Maxentius at the Battle of the Milvian Bridge in 312 CE because he viewed the Praetorians as too dangerous to survive.

He demolished their barracks, which effectively disbanded the institution, and scattered the remaining soldiers.

Although the Scholae Palatinae may have originated under Diocletian, Constantine expanded their role to serve as the new palace guard drawn from provincial cavalrymen. 

Their disappearance largely removed the last internal military threat to imperial succession.

For over three centuries, the Praetorian Guard had exercised power from within the walls of Rome, but their history clearly shows how armed loyalty eroded civil authority and became a tool for personal gain.