How the Roman Republic Became the Roman Empire

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Podcast Transcript

The Roman Republic existed for almost 500 years. The Romane Empire then existed for almost another 500 years. 

The two institutions had a great deal in common, but they radically differed in how Rome was administered. 

The Republic was set up explicitly to prevent the rule of a single individual, and yet, during the empire, that is exactly what happened. 

Learn more about how the Roman Republic became the Roman Empire on this episode of Everything Everywhere Daily.


In a previous episode, I discussed the difference between the Roman Republic and the Roman Empire. Julius Caesar is largely considered by historians to have been the last leader of the Roman Republic, and his posthumously adopted son Octavian, later called Augustus, is considered to be the first Roman Emperor. 

However, this change didn’t happen overnight. 

When we think of an empire, we think of a single state that controls a large amount of land and has conquered other nations. However, the Roman Republic had already been doing that. Using that definition, the Roman Republic was an empire. 

What made the Roman Empire an empire was the existence of an emperor. Strangely enough, there wasn’t an official legal position in Rome called an emperor.  


The English word emperor comes from the Latin word imperator. An Imperator was someone who held imperium, which meant legal authority. A general had imperium over his troops. A magistrate had imperium over a particular region or a particular jurisdiction. One person’s imperium could be greater than another person’s imperium. 

If having imperium made someone an emperor, then many people in Roman history would have been emperors because they had imperium.

So, to understand how the empire came about and how the position of what we call an emperor developed, we have to go back to the unique circumstances at the end of the republic.

Julius Caesar was an extremely talented general and an extremely ambitious politician. His ambition sparked a civil war, which he won and resulted in his being declared dictator for life. 

The idea of a dictator for life didn’t sit well with the senatorial class, so they conspired and assassinated Caesar in 44 BC. 

After Caesar was dead, the conspirators didn’t receive the hero’s welcome they thought they would receive. The plebeian Romans actually liked Caesar. The end result was yet another civil war. 

In his will, Caesar, the wealthiest person in Rome at this point, posthumously adopted his great-nephew Octavian as his son and also bequeathed him ? of his fortune. 

Octavian immediately began using the same name as his now adopted father, Gaius Julius Caesar. Historians will usually use Caesar to refer to Julius Caesar. However, Octavian now began to call himself Caesar, which he did for the rest of his life. 

This was done to give himself what the Romans called dignitas. When Caesar was later declared a god in 42 BC, it was so Octavian could say he was the son of a god, further increasing his dignitas

The years after Caesar’s assassination were tumultuous. Octavian fought Caesar’s right-hand man, Marc Antony. They later reconciled and fought the Senate, won, formed a new triumvirate, turned on each other, and began a new civil war, in which Octavian came out on top. 

In 30 BC, Octavian was now the last man standing and the most powerful man in Rome. 

However, this did not make him an emperor. 

Octavian wasn’t the military commander that Julius Caesar was. However, he was a much more shrewd politician and statesman. 

Caesar’s mistake was in accepting the position of dictator for life. By doing so, he positioned himself as a tyrant and earned the enmity of the Senate.

Octavian knew the key was to have power but not to look like he had power. 

On January 13, 27 BC, Octavian famously gave up his control of the provinces he governed and all the armies he controlled. 

This abandonment of power was mostly for show. He still controlled a vast fortune, and most soldiers felt a personal loyalty to him, as they did to Julius Caesar. He was also still, legally, a consul, the highest authority in Rome. 

Moreover, no one wanted to see a return to civil war, which they felt was a risk if Octavian had just walked away from his power. Octavian was a stabilizing force in Roman society, regardless of what you thought of him.

The Senate didn’t want Octivan to give up power, so they granted him a ten-year extension on his control over the provinces. Octavian feigned reluctance, but again, it was for show. 

He didn’t want to make the same mistake Caesar did by appearing too ambitious and too greedy for power. Whatever power he had appeared to have been constitutionally given to him by the Senate through legal channels. 

Also, just three days after Octavian threatened to give up power, the Senate bestowed upon him the title of Augustus, which roughly translates to “illustrious one.” This is usually the point where most historians mark the beginning of the Roman Empire. 

He was also given the title of princeps senatus, which simply means the first senator. The princeps senatus was not an official position. It was simply the person listed first on the member rolls and was usually the most esteemed member of the Senate. 

It was from this title that the terms princeps and principate were derived. Augusts would often call himself princeps as it implied he was simply the first among equals and was much more humble sounding than a dictator. More on the princeps in a bit. 

By 23 BC, after having served as consul for eight consecutive years from the year 30 BC, Augustus realized that he needed to change his approach. There were two consuls appointed every year, and it was the ultimate honor in Roman society….and he was hogging one of them.

So, he stepped down from being consul. As he was no longer officially a consul, the Senate instead granted him the powers of the tribune of the plebs for life…. but not the title. 

This made his person sacrosanct. He also had the power to convene the Senate, veto any laws, submit bills before the Senate and the People’s Assembly, speak first at any assembly, and oversee elections. 

He was also given the right to supervise public morals, a right normally given to censors.  

If this sounds like wide-ranging power, it was. However, it wasn’t absolute. All of his powers existed in other constitutional offices. The Senate and the rest of the positions on the Cursus Honoram still existed. 

The senate offered him the power to make his word law, and he turned it down. The reason was having that power basically made him a dictator, and it wasn’t a good look. Furthermore, it wasn’t necessary as he basically had all the power he needed. 

In 19 BC he was also given consular authority and imperium within Rome that superseded the imperium of everyone else, including consuls. 

When the military was successful in one of the provinces he controlled, he was given credit. When they were successful in a senatorial province, he was still given credit because he was the princeps senatus. The end result was that no one was allowed to have a triumph other than him. 

In 12 BC, his former Triumver Lepidus died, who also held the position of Pontifex Maximus, the highest religious figure in the Roman religion. That was a lifetime position, which was then given to Augustus. 

In 2 BC, he was given the title pater patriae, or “father of the country.”

There was one other thing that Augustus did that helped establish the power of the emperor….he lived a really long time. 

When Julius Caesar died, Octavian was only 18 years old, and he was thrust into power at a very young age. He was 36 when he was proclaimed Augustus. He managed to live to the age of 75. 

By the time he died, and given the life span of the average Roman, almost no one could remember the days of the Republic.  The powers given to Augustus were the norm. 

Augustus was also smart in that he accumulated powers without actually holding the office, and he did so gradually over a period of decades. He was willing to forgo the powers given to him, which he felt were too much. 

He achieved everything Julius Caesar wanted to do, but without making the same mistakes.  

There was, however, a problem. All of these honors were given to him as a person. There wasn’t an office that held all of these powers that someone else could fill. 

When Augustus died in the year 14, there was a question as to what would happen. Augustus, after having many other close relatives die unexpectedly, ended up selecting his stepson Tiberius as his successor. 

Before he died, he extended many of his powers to Tiberius, including his tribunate and proconsular powers. In his will, much of his wealth was given to Tiberius. He also legally adopted Tiberius as his son. 

Just a few weeks after the death of Augustus, the senate bestowed upon Tiberius the title of princpes and augustus and he was also elected Pontifex Maximus. 

As the adopted son of Octavian Gaius Julius Caesar, he too was able to use the name Caesar. 

Most importantly, the Roman system, by this time, had become accustomed to being run by a single individual. 

This system of collected powers and titles became known as the principate. 

The powers and honors bestowed upon the princeps expanded over time. One of the few documents we have that outlines the powers of the princep was the Lex de imperio Vespasiani, a document created after the ascension of Emperor Vespasian in the year 69. 

The Lex de Imperio Vespasiani is only the second part of a two-page document, but it provides a partial list of the powers of the emperor. In it, it gives the emperor the powers to endorse candidates for office and expand the boundaries of the city, as well as the power to do anything “he believes, in the interests of the State … that he should do.”

The powers clearly had expanded by this time, but they were still, at least in theory, given by the Senate to keep up the illusion of the republic. Vespasian wasn’t related to previous emperors but still used Caesar as a title, which is something all subsequent emperors did. 

The principate lasted from 27 BC until the year 284 and the rise of Emperor Diocletian.  Diocletian changed the nature of the role of emperor and began a period known as the dominate. Dominate comes from the word dominus, which means ‘lord.’

The dominate differed from the principate in that the Empire became much closer to a monarchy. Diocletian split up the empire into halves, each of which was to be ruled by a senior augustus and a junior caesar. The caesar was to be groomed to take over for the augustus. 

For all practical purposes, the emperor was an autocrat whose word was law. However, throughout the Roman Empire, the senate did at least rubber stamp every new emperor. The official list of emperors, as opposed to those who claimed to be emperor, is determined by those who were approved by the senate. 

The reason why the imperial system was created, and the reason why there was something we call a Roman emperor, was due to the slow accumulation of power over a period of decades by Augustus. 

Those powers and titles that he accumulated were then passed down in a bundle, approved by the Roman senate, to the men we think of today as Roman Emperors.