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Why did the princeps/emperors of various dynasties prior to Constantine the Great (d.337 AD) allow the Praetorian Guard to continue to amass such power and repeatedly cause trouble, including palace coups?

It would appear that the Praetorian Guard gained their reputation for having some power over the principate, rather than the principate or dominate having power over them, with the rise of Sejanus who consolidated the Praetorian Guard into one camp under a prefecture. Prefects of the Praetorian Guard would prove to be troublesome from that time, but the Praetorian Guard remained problematic as an institution even if prefects were executed.

There were notably different units of guards who were chosen by the emperor himself to protect him. (The Imperial German Bodyguard, the Speculatores, and the and Equites Singulares). Despite this, the Praetorian Guard remained powerful.

If the Praetorian Guard and its prefecture created repeated problems then why were they not restructured or reduced? Why not circulate elite veterans of various legions or rotate the Guard?

The only compelling reason I can think of is the need to have absolute discretion and trust, but this is probably why the Princeps rotated their personal bodyguards. The Praetorian Guard were the only ones allowed to be armed in certain areas of Rome, and their loyalty was to the 'Emperor' first before the Roman Senate or People. Perhaps it was problematic to rotate other units of the legions through the Guard as the Praetorian Guard was specifically loyal to the institution of the principate.

Constantine the Great, who seemed to be adept at consolidating imperial power, finally dissolved the Praetorian Guard in around 313 AD.

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    I've been wondering about that too, recently. – Felix Goldberg Oct 26 '17 at 7:21
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    I suspect you'll find the answer somewhere along the lines of "Morale is the state of mind. It is steadfastness and courage and hope. It is confidence and zeal and loyalty. It is élan, esprit de corps and determination" - George C. Marhshall – J Asia Oct 26 '17 at 9:27
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tl;dr

Why didn't Roman emperors restructure or dismantle the Praetorian Guard?

Several tried. It didn't end well for them. Most paid for the attempt with their lives.


Although most people tend to think of the Praetorians in the context of the Roman Emperor, they had actually existed long before Rome became an empire. During the Roman Republic, generals or magistrates (called "praetors") had groups of soldiers known as Praetorian Cohorts assigned to them.

The number of Praetorians grew considerably during the civil wars that were initiated by Caesar's crossing of the Rubicon. Both Augustus and Mark Antony had several Praetorian Cohorts. When Augustus became emperor, he united the Praetorian Cohorts into the Praetorian Guard. He had learned firsthand the advantages of having a military force that was loyal to him, personally.

Augustus maintained several cohorts in Rome and dispersed the rest to other Italian cities. Their influence grew substantially under Augustus' heir, Tiberius, and his Praetorian Prefect, Sejanus.

When Tiberius retired to Capri in the last decade of his reign, Sejanus became the administrative head of Rome and, effectively, the leader of the empire. Sejanus passed numerous reforms that favouring the Praetorian Guard. In particular, he moved them from the outskirts of Rome into the city itself and built their barracks (the Castra Praetoria) which would become the Praetorian Guard's headquarters for the next three centuries.

From that point, the Praetorian Guard became simply too powerful to challenge by anyone who didn't have an army at their backs. They could make and break emperors. For example, the guard was instrumental in the removal of Gaius (Caligula) in AD 41, and Nero in AD 68.

The case of Gaius is instructive. in 40 AD, Gaius had announced his intention to leave Rome permanently to the senate. He meant to move to Alexandria in Egypt. This move would have removed much of the power and influence of both the senate and the Praetorian Guard. He was murdered the following year, and the Guard proclaimed his uncle Claudius emperor.

As mentioned above, the Praetorians were also instrumental in the overthrow of Nero, who they replaced with Galba. They then turned against Galba, replacing him with Otho. Otho committed suicide after just three months in power and was replaced by Vitellius.

One of Vitellius' first moves as emperor was to disband the Praetorian Guard. He also had more than 100 of them executed for their role in the murder of Galba. Vitellius created a new guard comprised of Germanic troops who were loyal to him.

Most of the surviving Praetorians pledged their loyalty to Vespasian. When he became emperor, the Praetorian Guard was restored in order to bring order back to Italy in the aftermath of the "Year of the Four Emperors".

Time and again, the Praetorians would involve themselves in Imperial politics. When the emperor Pertinax decided to reform the Praetorian Guard in 193, on the grounds that it had become too powerful and corrupt, the response of the Guard was to murder the emperor and auction the empire to the highest bidder!

(In case you're interested, Didius Julianus won the auction. He would reign for a whole nine weeks.)

It wasn't until Constantine that Rome had an emperor with the power (and sufficient military force at his back) to disband the Praetorian Guard.

The Guard had sided with Maxentius in the civil war, but he was decisively defeated and killed at the Battle of the Milvian Bridge in 312. Constantine dissolved the Praetorian Guard the following year, symbolically destroying their barracks in Rome and assigning surviving Praetorians to postings in the distant reaches of the empire, far away from the political centre.


Sources

Erdkamp, Paul: A Companion to the Roman Army, Wiley, 2011

Smith, R.E: The Army Reforms of Septimius Severus, Franz Steiner, 1972

Southern, Patricia: The Roman Empire from Severus to Constantine, Routledge, 2015

Southern, Patricia, & Dixon, Karen R: The Late Roman Army, Yale, 1996

Speidel, M.P: Maxentius and His "Equites Singulares" in the Battle at the Milvian Bridge, Classical Antiquity, Vol 5, No 2 (Oct 1986), pp 253-262.

  • Thanks for a detailed answer and history. I suppose it does and does not answer the question completely. I suppose the princeps were effectively hostages in their own palaces if they chose to go after the Praetorians? Why not bring in legions to take them on? At times it sounds like they reached the power of the Seljuk Turks in relation to the Abbasid Caliphate or the power of the Shogun and Samurai at certain points in the Empire of Japan. I am just trying to grasp how that happened in Rome with other legions. It would seem the Senate or Principate or other legions could reign them in. – Seanchaí Oct 26 '17 at 11:44
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    @Seanchaí Most legions were stationed on the frontiers of the empire, where they were needed. Bringing one (or more) to Rome to remove the Praetorians could just as easily have started another civil war (and if that happened, there was no guarantee that the emperor who started it would still be emperor when it ended!). – sempaiscuba Oct 26 '17 at 11:58
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    @sempaiscuba Great answer! I remember reading recently but my ancient brain can't recall the details that when one of the Emperors (Caligula?) was murdered, the senators planned a return to the Republican system. As this would have stripped the Praetorian Guard of its power base, they declared Claudius Emperor. Have I got it completely wrong? (I'm prepared for the answer Yes ;-) ) – TheHonRose Oct 26 '17 at 21:30
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    @TheHonRose Josephus certainly claimed that the Senate attempted to use Caligula's death as an opportunity to restore the republic, but the military remained loyal to Claudius. – sempaiscuba Oct 26 '17 at 22:03
  • Besides harbouring weird geopolitical plans, Caligula also made the mistake of taunting and insulting several leading Guards officers. I wonder if that did not have more to do with his murder. But +1 of course. – Felix Goldberg Oct 27 '17 at 5:04

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