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— CH. 1 · ORIGINS OF THE PRINCIPATE —

Roman emperor

~6 min read · Ch. 1 of 7
7 sections

  • In 27 BC, Octavian and the Senate concluded a political agreement known as the First Settlement. This moment marked the formal beginning of the Roman Empire under the title princeps, meaning first among equals. Octavian had spent years consolidating power after defeating Mark Antony at Actium in September 31 BC. He returned to Rome claiming he would restore the Republic, yet he retained control over almost all provinces for ten-year terms that he could renew indefinitely. The Senate granted him the honorific augustus, which denoted elevated status rather than legal kingship. Augustus held supreme military command through imperium maius, giving him authority over all troops without time limits. He also assumed tribunician power in 23 BC, allowing him to veto magistrates and propose laws while remaining technically subordinate to the Senate. Ancient writers like Plutarch and Tacitus viewed Julius Caesar as the last dictator, whereas modern historians mark 27 BC as the start of imperial rule. Most Romans simply saw the emperor as whoever ruled the state, regardless of specific titles or offices.

  • Diocletian introduced reforms in 285 AD that transformed the empire into an absolute monarchy called the Dominate. Emperors adopted the diadem crown as their supreme symbol of power, abandoning the subtle republican pretenses of earlier centuries. Diocletian declared himself Jovius, the son of Jupiter, making anything related to him sacred. The emperor no longer needed Senate ratification for his powers, becoming the sole source of law. New laws were given directly to praetorian prefects instead of being shared publicly with the Senate. Consuls continued to be appointed each year, but by this point the office was often occupied by the emperor himself. Anastasius I became the last known emperor to use tribunicia potestas at the start of the 6th century. Constans II was the final Eastern emperor to visit Rome before the title of consul fell into disuse entirely. The personal court and administration traveled alongside the ruler, rendering the Senate's role redundant. This shift from princeps to dominus symbolized the complete transformation of government structure over three hundred years.

  • The Augustan institution lacked a clear succession system, forcing emperors to adopt candidates as sons rather than announce heirs formally. Primogeniture held no relevance in early Empire politics, though Tiberius married Julia the Elder to maintain family connections. Vespasian broke tradition by openly declaring his sons Titus and Domitian as sole heirs after the Year of the Four Emperors collapsed. Commodus died in 192 AD at the hands of his own soldiers, ending a dynasty that had ruled since Augustus. From that death until the 5th century, scarcely a decade passed without succession conflicts or civil war. Very few emperors during this period died of natural causes. Legitimacy depended on acceptance by the Roman army rather than any legal criteria. Septimius Severus declared himself the adoptive son of Marcus Aurelius to strengthen his claim. Many usurpers were retroactively recognized as legitimate once they defeated rivals or gained Senate approval. Maxentius controlled Rome for several years despite lacking recognition from the Tetrarchs. The year 193 became known as the Year of the Five Emperors due to multiple simultaneous claims to power.

  • Diocletian established the Tetrarchy in 285 AD to provide smoother succession and greater continuity of government. This system placed two senior emperors called augusti alongside two subordinates serving as caesares who would succeed them. When Diocletian retired in 305 AD, his caesar succeeded him and appointed a new subordinate. Each pair ruled over half the empire, creating permanent Western and Eastern divisions. Constantine I reunited the empire in 324 AD but imposed hereditary succession principles Diocletian had intended to avoid. Theodosius I died in 395 AD, leaving his sons Honorius and Arcadius to rule separate halves permanently. Milan and later Ravenna served as capitals for the West while Constantinople remained the Eastern seat. Julius Nepos continued claiming the title until his murder in 480 AD after being expelled to Dalmatia. Odoacer shipped imperial regalia to Emperor Zeno in Constantinople following Romulus Augustulus's overthrow in 476 AD. Historians mark this date as the fall of the Western Roman Empire, though territory had already reduced to Italy alone.

  • Constantine the Great moved the capital from Rome to Constantinople in 330 AD, formerly known as Byzantium. He became the first Christian emperor, establishing the idea that rulers were God's chosen protectors on earth. Emperors after Theodosius I saw themselves as heads of the Church under what scholars term Caesaropapism. The absolute power of the Roman emperor increased with the advent of Christian ideas according to George Ostrogorsky. Heraclius began using basileus as the traditional Greek title for monarchs starting in 629 AD. Michael I Rangabe was the first emperor to actually use the full title Roman emperor in official documents. The Byzantine state followed a model where the emperor played ruler and head of Church roles simultaneously. A formal coronation performed by the Patriarch of Constantinople became standard procedure. Political and secular power often remained distinct despite theoretical unity between church and state. Muslim conquests of the 7th century gave Byzantine imperialism new purpose and sense of divine mission.

  • The Eastern Empire survived another thousand years after the Western collapse in the late 5th century. Italy was recovered during Justinian I's reign but reverted to Lombard control by the end of the 6th century. Rome fell to the Lombards in 751 AD during Constantine V's reign after being surrounded completely. Pepin the Short defeated them and received favor from Pope Stephen II, who became head of Papal States. Charlemagne was crowned Imperator Romanorum by Pope Leo III on Christmas Day 800 AD, ending recognition of Eastern emperors. Western rulers began calling the Empire the Greek Empire while regarding themselves as true successors. The line of Eastern emperors continued until Constantinople's sack in 1204 AD created three exile lines: Nicaea, Trebizond, and Thessalonica. Nicean rulers recovered Constantinople in 1261 AD and restored the empire traditionally. The Empire of Trebizond existed for two hundred more years using modified titles since 1282 AD. Constantinople finally fell to Ottoman Turks in 1453 AD when last emperor Constantine XI Palaiologos died in battle. Morea and Trebizond fell in 1461 AD, marking the final extinction of Byzantine imperial authority.

  • The title imperator dates back to 189 BC when Aemilius Paulus won Rome's first attested triumph. Pompey and Sulla held the title with great pride before Julius Caesar assumed it as a proper name. Augustus used Imperator instead of his first name, becoming Imperator Caesar rather than Caesar Imperator. Tiberius, Caligula, and Claudius avoided using the title initially, though Caligula was hailed imperator by the Senate on accession. Nero's late reign saw imperator return to nomenclature in 66 AD, after which virtually all emperors adopted it. Vespasian made imperator the main appellation of the ruler, transforming its original military meaning into sovereign power. Diocletian introduced dominus noster addressing emperors as our Lord while imperator continued usage. Aurelian officially adopted dominus in coinage starting around 270 AD. The East translated imperator as autokrator, meaning self-ruler, until the empire's end. Michael III and Basil I issued coins in 866-867 AD addressed as imperator and rex respectively. Charlemagne transformed imperator into the official Latin title of the Holy Roman Empire. Caesar evolved from Gaius Julius Caesar's cognomen into heir apparent designation before becoming part of imperial formula. Justinian II awarded caesar to Tervel of Bulgaria in 705 AD, losing its imperial character entirely.

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Augustus (title)

Common questions

When did the Roman Empire officially begin under Octavian?

The Roman Empire formally began in 27 BC when Octavian and the Senate concluded a political agreement known as the First Settlement. This event marked the start of imperial rule under the title princeps, meaning first among equals.

What reforms did Diocletian introduce to transform the Roman government structure?

Diocletian introduced reforms in 285 AD that transformed the empire into an absolute monarchy called the Dominate. Emperors adopted the diadem crown as their supreme symbol of power and abandoned the subtle republican pretenses of earlier centuries.

How did succession work for early Roman emperors before the Tetrarchy system?

The Augustan institution lacked a clear succession system, forcing emperors to adopt candidates as sons rather than announce heirs formally. Legitimacy depended on acceptance by the Roman army rather than any legal criteria or primogeniture rules.

Which emperor moved the capital from Rome to Constantinople and when did this occur?

Constantine the Great moved the capital from Rome to Constantinople in 330 AD, formerly known as Byzantium. He became the first Christian emperor and established the idea that rulers were God's chosen protectors on earth.

When did the Eastern Roman Empire finally fall to Ottoman Turks after surviving another thousand years?

Constantinople fell to Ottoman Turks in 1453 AD when last emperor Constantine XI Palaiologos died in battle. Morea and Trebizond fell in 1461 AD, marking the final extinction of Byzantine imperial authority.

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All sources

91 references cited across the entry

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  4. 4inlineEutropius, Breviarium 7.8 "From that period he held the government as sole ruler for forty-four years, for during the twelve previous years he had held it in conjunction with Antony and Lepidus. Thus
  5. 5inlineJerome, Chronichon, 184th Olympiad. "2nd ruler of the Romans, Octavianus Caesar Augustus reigned for 56 years and 6 months; from whom the kings basileus of the Romans are called Augusti."
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  74. 74inlineRes Gestae I.7, "For ten years in succession I was one of the triumvirs for the re-establishment of the constitution. To the day of writing this June/July AD 14 I have been princeps senatus for forty
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