Roman Emperors Who Changed the Course of History

Certainly, the Roman Empire, throughout its long history, had several emperors who significantly impacted the course of events. World History Edu presents ten Roman emperors whose actions and reigns were especially influential:

Augustus (r. 27 BC – 14 AD)

After his victory at the Battle of Actium and the subsequent defeat of Mark Antony and Queen Cleopatra of Egypt, Augustus effectively ended the Roman Republic, which had been in existence for nearly five centuries. Image: Augustus as Roman pharaoh in an Egyptian-style depiction, a stone carving of the Kalabsha Temple in Nubia

Originally known as Octavian, he was the first Roman emperor, establishing the principate, the foundational system of Roman imperial government. He brought about the Pax Romana, a period of relative peace and stability.

Augustus, who was the adopted son of Roman dictator and general Julius Caesar, overhauled the Roman administrative and taxation system, laying down a foundation that would serve the empire for centuries.

He expanded the empire’s borders, securing its frontiers, especially in areas like Spain, Gaul, and the Balkans, and annexing regions like Egypt.

Also, he established the Praetorian Guard, an elite unit intended to protect the emperor. Over time, however, they would play significant roles in the political intrigue of the empire.

In the nutshell, Augustus’ reign set the standard for subsequent emperors. The title “Augustus” became synonymous with the position of the emperor, and his model of governance heavily influenced the subsequent history of Rome.

Nero (r. 54-68 AD)

Emperor Nero

Nero’s reign was marked by extravagance, the persecution of Christians, and massive public works projects. His rule ended in a revolt, and his death marked the beginning of the Year of the Four Emperors.

Nero, Rome’s fifth emperor and the final of the Julio-Claudian dynasty, is one of the most controversial emperors in Roman history. His reign was characterized by both significant cultural contributions and notorious episodes of excess and cruelty.

A massive fire consumed much of Rome over six days. While it’s uncertain how the fire started, rumors spread that Nero himself had set the fire to clear land for his Domus Aurea, a lavish palace complex. This gave rise to the infamous, though likely apocryphal, image of Nero “fiddling while Rome burned.”

Following the Great Fire, Nero blamed Christians for the catastrophe, leading to severe persecutions. Many Christians were arrested, tortured, and executed, with some being burned alive as nighttime illuminations in the imperial gardens.

After the fire, Nero commissioned the construction of the Domus Aurea (“Golden House”), an enormous and opulent palace complex that covered parts of central Rome. This architectural wonder included an artificial lake, gardens, and a colossal statue of Nero himself.

The later years of Nero’s reign were marked by unrest and military revolt, most notably the rebellion led by Vindex in Gaul and by the legate of Hispania, Galba. Nero’s lack of popularity with the Senate and the Roman elite, combined with these revolts, led to his downfall.

Facing a loss of support and the advancing forces of Galba, Nero chose to commit suicide in 68 AD, famously lamenting, “What an artist dies in me!”

His death marked the end of the Julio-Claudian dynasty and initiated the chaotic “Year of the Four Emperors.”

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Vespasian (r. 69-79 AD)

As the founder of the Flavian dynasty, he restored stability after the Year of the Four Emperors. He also initiated the construction of the Roman Colosseum.

Vespasian, who reigned as Roman emperor from 69 AD to 79 AD, was the founder of the Flavian dynasty, succeeding the short-lived Year of the Four Emperors. His reign was marked by stability, economic reforms, monumental building projects, and military achievements.

Perhaps the most iconic of Vespasian’s contributions to Rome was the construction of the Flavian Amphitheatre, better known as the Colosseum. Built on the site of Nero’s drained lake from the Domus Aurea, the Colosseum served as a gift to the Roman people and a symbol of the Flavian dynasty’s commitment to public welfare.

Vespasian, with his son Titus, quelled the Jewish Revolt in Judaea, leading to the capture of Jerusalem in 70 AD. The Arch of Titus in Rome commemorates this victory.

Vespasian worked diligently to establish his family’s legacy, grooming his sons Titus and Domitian to succeed him.

He famously joked about his own mortality and the financial needs of the empire. On his deathbed, he’s reputed to have said, “Dear me, I think I’m becoming a god!” referencing the Roman practice of deifying emperors after their death.

READ MORE: Last Words of Famous Figures in History

Trajan (r. 98-117 AD)

Emperor Trajan

Trajan is known for his ambitious military campaigns that expanded the empire to its maximum territorial extent.

Trajan, who reigned as Roman emperor from 98 AD to 117 AD, is often remembered as one of the “Five Good Emperors” of the Roman Empire. His rule was characterized by military expansion, significant infrastructure development, and benevolent governance.

One of Trajan’s most significant contributions was his military expansion. He embarked on two major campaigns, which resulted in the annexation of Dacia (modern-day Romania) and a vast expansion into the eastern territories, including parts of the Parthian Empire like Armenia, Mesopotamia, and the Nabatean Kingdom.

The conquest of Dacia brought immense wealth into the empire, especially from Dacian gold mines. Trajan used this wealth for public works and to alleviate the burden of taxes on the provinces.

Trajan initiated extensive building projects throughout the empire. In Rome, the most significant was the Trajan’s Forum, which included Trajan’s Column, a monumental column that chronicled his victory in Dacia. He also commissioned the construction of roads, bridges, aqueducts, and harbors, which facilitated trade and movement throughout the empire.

Apart from monumental structures, Trajan invested heavily in essential civic infrastructure. The Aqua Traiana, a new aqueduct for Rome, ensured the city had a fresh water supply.

Unlike many of his predecessors, Trajan enjoyed a good relationship with the Roman Senate. He was known for ruling with the Senate’s advice, thereby maintaining a harmonious political environment.

Hadrian (r. 117-138 AD)

Hadrian, Trajan’s successor, fortified the empire’s frontiers and built Hadrian’s Wall in Britain. He also made significant contributions to Roman architecture.

Similar to his predecessor, Trajan, Hadrian is considered one of the “Five Good Emperors” of the Roman Empire.

However, unlike Trajan, Hadrian believed in consolidating and fortifying the empire’s existing territories rather than pursuing further expansion. He reinforced this belief by withdrawing from some of the eastern territories that Trajan had conquered.

Demonstrating his emphasis on fortification, Hadrian ordered the construction of a stone wall (known as Hadrian’s Wall) across the width of Britain to keep out the Picts and other northern tribes. This wall stands as one of the most significant Roman legacies in Britain.

Hadrian was a patron of the arts and architecture. The Pantheon in Rome, with its iconic dome, was rebuilt under his orders and stands as a testament to Roman architectural prowess.

Unlike many emperors, Hadrian carefully planned his succession. He adopted Antoninus Pius on the condition that Antoninus would, in turn, adopt Marcus Aurelius, ensuring a stable transition of power.

READ MORE: List of Roman Deities and their Greek Equivalents

Marcus Aurelius (r. 161-180 AD)

Marcus Aurelius

Known as the philosopher emperor, Marcus Aurelius’ reign is noted for his Stoic philosophy and the challenges he faced with the Marcomannic Wars and internal strife.

Marcus Aurelius, who ruled as Roman Emperor from 161 to 180 AD, is often remembered not only as a political leader but also as a philosopher-king. His reign was marked by military challenges, especially the Marcomannic Wars, as well as his dedication to Stoic philosophy, which he documented in his personal notes, now known as “Meditations.”

Marcus Aurelius is credited with enacting laws that protected slaves, children, and the impoverished. He also sought to appoint competent and just administrators, placing emphasis on virtue and ability rather than solely on aristocratic birth.

One criticism of Marcus’s reign was his choice of successor. His son, Commodus, who succeeded him, is often deemed one of Rome’s more problematic emperors. Marcus’s decision to break with the adoptive tradition of the “Five Good Emperors” and instead pass the throne to his biological son had lasting repercussions for the empire.

Constantine the Great (r. 306-337 AD)

Constantine the Great, the Roman emperor was the son of Emperor Constantius I. Having defeated the likes of Licinius and Maxentius by 324, he became the sole ruler of the empire.

One of the most significant aspects of Constantine’s reign was his conversion to Christianity. While the exact nature and timing of his conversion are debated, the Battle of the Milvian Bridge in 312 AD stands out, where, according to sources, he saw a vision of the Christian cross and was assured victory with the words “In this sign, you will conquer.” He emerged victorious and attributed his success to the Christian God.

In 313 AD, Constantine and his co-emperor Licinius issued the Edict of Milan, which granted religious tolerance to Christians throughout the empire. It marked the beginning of the end for state-sponsored persecution of Christians, allowing the Christian community to emerge from the shadows and grow rapidly.

He initiated various administrative and economic reforms. He introduced the “solidus,” a gold coin that became a stable and standard currency for centuries. He also divided the empire into smaller provinces grouped into larger administrative districts called ‘dioceses’ for more effective governance.

Recognizing the strategic and economic significance of Byzantium, Constantine refounded and expanded the city, renaming it Constantinople (modern-day Istanbul) in 330 AD. This city would later become the capital of the Byzantine Empire and serve as a vital Christian stronghold for a millennium.

Constantine’s rule also saw the end of the Tetrarchic system, a system of multiple rulers governing the vast Roman Empire. By the time of his death, Constantine had consolidated power, ruling as a sole emperor.

Theodosius I (r. 379-395 AD)

Theodosius the Great made Christianity the state religion of the Roman Empire and was the last emperor to rule both the Eastern and Western halves of the empire.

Theodosius I, also known as Theodosius the Great, was the last emperor to rule both the Eastern and Western Roman Empires before they were permanently divided into two separate entities. Under Theodosius, pagan practices and ceremonies were progressively outlawed. Temples were closed, sacrifices were banned, and the ancient Olympic Games, a cornerstone of Hellenic tradition, were prohibited due to their pagan origins.

He convened the First Council of Constantinople in 381 AD, which reaffirmed the tenets of Nicene Christianity and further marginalized Arianism. This council also expanded the Nicene Creed, which is still used in many Christian denominations today.

Upon his death in 395 AD, the empire was permanently divided between his two sons, with Honorius receiving the West and Arcadius the East. This division paved the way for the eventual fall of the Western Roman Empire and the survival and flourishing of the Eastern Roman Empire (Byzantine Empire).

Justinian I (r. 527-565 AD)

Justinian I

An emperor of the Eastern Roman (Byzantine) Empire, Justinian the Great is known for his ambitious attempt to reconquer the Western Roman Empire and for his codification of Roman law, known as the “Corpus Juris Civilis.”

Justinian I, known as Justinian the Great, ruled the Byzantine Empire (often referred to as the Eastern Roman Empire) from 527 to 565 AD. His reign was transformative, leaving a lasting impact on the empire and the wider world.

Arguably Justinian’s most enduring legacy is the codification of Roman laws. This massive legal undertaking culminated in the “Corpus Juris Civilis,” which became the foundation for much of European legal thought. It comprised the “Codex” (a compilation of existing laws), the “Digest” (a compilation of legal opinions), the “Institutes” (a legal textbook), and the “Novellae” (new laws). This code would influence legal systems for centuries, particularly during the Renaissance when it was “rediscovered” and subsequently impacted the development of modern legal codes.

After the Nika Riots (in 532 AD) resulted in the burning of the original Hagia Sophia church, Justinian commissioned the construction of a new Hagia Sophia. This architectural marvel, with its vast dome, became the center of Orthodox Christianity and remains one of the world’s most iconic buildings.

Diocletian (r. 284-305 AD)

To address the vastness and diversity of the empire, Diocletian introduced the tetrarchy system, where four emperors would rule the empire, two Augusti and two Caesars. He also initiated the last major persecution of Christians.

Recognizing the vastness and complexity of governing the Roman Empire, Diocletian introduced the Tetrarchy (rule of four). He appointed Maximian as his co-emperor (or “Augustus”), and each of them had a junior co-emperor or “Caesar.” This system ensured smoother transitions of power and allowed for the vast territories to be governed more effectively.

Diocletian’s reign is infamous for the empire’s last and most severe persecution of Christians, which began in 303 AD. Churches were destroyed, scriptures were burned, and many Christians were tortured or executed.

In order to counteract the economic turmoil and inflation, Diocletian introduced new, more stable coinage. He established mints and attempted to stabilize the empire’s economy through these monetary reforms.

In a move almost unprecedented among Roman emperors, Diocletian voluntarily abdicated the throne in 305 AD, believing that he was too old to govern effectively. He retired to his palace in modern-day Croatia, where he spent his last years gardening.

The crisis only came to an end when Diocletian (reign: 284-305) came to power in 284, at which point he proceeded to divide the empire into the eastern and western part.


Each of these emperors, through their decisions, policies, and personal characteristics, played a pivotal role in shaping the history and trajectory of the Roman Empire and even empires that followed after its demise.

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