Roman emperors did not all wield power in the same way. Some built durable institutions; some stretched the empire’s borders; others changed the terms on which Rome governed, worshipped, or imagined itself. A list of “greatest” rulers can easily become a parade of familiar names, so this guide looks instead at emperors whose decisions left a lasting mark on the Roman world.
That means the choices below are not a ranking of personal virtue. Nero, for example, remains famous because ancient writers and later tradition made him a symbol of imperial excess. Augustus and Constantine belong here for a different reason: the political settlements created in their reigns outlasted them by generations.
1. Augustus (27 BCE–14 CE): the man who made emperors possible
Augustus emerged from the violence that followed Julius Caesar’s assassination and turned a shattered republic into an imperial system. He carefully retained republican language while concentrating military command, finances and political authority in his own hands. The arrangement became the model his successors inherited.
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His reign also set the visual and civic language of empire. Temples, forums and monuments made rule visible in Rome and across the provinces. The Met’s chronology of the early empire notes that the death of Augustus in 14 CE brought Tiberius to power and made dynastic succession an established principle rather than an emergency solution.
2. Claudius (41–54): the unlikely administrator
Claudius was not the obvious candidate for power after Caligula’s assassination, yet his reign shows why Roman history cannot be reduced to battlefield fame. He expanded the imperial bureaucracy, relied on freedmen in administration, and made the conquest of Britain a major imperial project. His government also absorbed new provincial elites into the Roman political world.
Ancient sources were often hostile to Claudius, particularly because they disliked the influence wielded by court insiders. That hostility should be read carefully. His administration left a more organised imperial state than the one he inherited.
3. Vespasian (69–79): restoring order after civil war
The year 69 brought four competing emperors in quick succession. Vespasian’s victory founded the Flavian dynasty and stabilised a state battered by military revolt and political uncertainty. He put imperial finances on firmer footing and began the amphitheatre later known as the Colosseum, a project that connected the new dynasty to the centre of Rome.
His importance lies in recovery. The empire did not need another theatrical claimant; it needed a ruler capable of making an exhausted system function again.
4. Trajan (98–117): empire at its widest reach
Trajan’s reign is often remembered as the territorial high point of Roman power. His campaigns brought Dacia into the empire and briefly extended Roman control into Mesopotamia. Yet his influence cannot be measured on a map alone. The Forum of Trajan, Trajan’s Market and the column that still bears his name made military success part of Rome’s public landscape.
The expansion had costs, and some eastern gains proved difficult to hold after his death. Even so, Trajan became a benchmark against which later emperors were judged.
5. Hadrian (117–138): drawing the line
Hadrian made a deliberate choice that differed from Trajan’s: he consolidated. He withdrew from exposed eastern territories and invested in fortifications, administration and provincial travel. Hadrian’s Wall in northern Britain is the best-known surviving symbol of that approach, but the larger point was strategic. Roman power could not be defined only by continual expansion.
He also travelled extensively through the provinces, leaving buildings, benefactions and a more personal imperial presence in places far from Rome.
6. Marcus Aurelius (161–180): rule under pressure
Marcus Aurelius is often introduced as the philosopher-emperor because of the private reflections collected as Meditations. His reign, however, was not peaceful. It included war on several frontiers and the Antonine Plague, a crisis that affected the empire’s population and resources.
His place in this list comes from the contrast between ideal and circumstance. Marcus Aurelius is a reminder that even a ruler celebrated for self-discipline had to govern through military, economic and public-health pressures.
7. Septimius Severus (193–211): the military emperor’s new model
Septimius Severus came to power after another civil war and strengthened the army’s position within the state. He raised soldiers’ pay, founded a dynasty and campaigned in Africa and Britain. The changes helped secure his rule, but they also made the empire increasingly dependent on military loyalty and expenditure.
His reign belongs to the story of Rome’s transformation in the third century, when the balance between senate, court and army shifted dramatically.
8. Diocletian (284–305): rebuilding an empire in crisis
By the late third century, Rome had endured rapid turnover among emperors, invasions and financial strain. Diocletian responded by reshaping how the empire was governed. He divided authority among multiple rulers in the Tetrarchy, enlarged the administrative structure and attempted major tax and currency reforms.
The Tetrarchy did not survive intact after he retired, but the larger administrative and political changes did. Diocletian’s Rome was a more openly imperial, more bureaucratic state than Augustus’s.
9. Constantine (306–337): a Christian emperor and a new capital
Constantine’s influence reaches far beyond a single battle or building. After winning control of the empire, he supported Christianity and, with Licinius, issued the Edict of Milan in 313, permitting freedom of worship. He also founded Constantinople as a new imperial capital in 330.
The Met’s timeline records both developments as turning points in late Roman history. They did not make the empire instantly Christian or erase Rome’s importance, but they changed the political and religious direction of the Mediterranean world.
10. Theodosius I (379–395): the last ruler of a united empire
Theodosius I ruled both eastern and western halves of the empire before his death in 395. Afterwards, authority passed to his sons Arcadius in the east and Honorius in the west. The division had earlier precedents, but it became a lasting political reality.
His reign also intensified the state’s support for Nicene Christianity. Those changes belonged to a longer process rather than a single moment of conversion, yet they helped define the late Roman world inherited by Byzantium and medieval Europe.
Why “influential” does not mean uncomplicated
Roman emperors are unusually vulnerable to shorthand: the wise stoic, the mad tyrant, the conqueror, the reformer. The surviving evidence is uneven, much of it written by elite observers with their own political interests. A better way to read these rulers is to ask what changed during and after their reigns: succession, frontiers, administration, cities, religion and the relationship between the army and the state.
For another side of imperial power, see our guide to how Roman emperors were turned into gods in ancient Rome.
