Roman Emperors: Timeline and the Most Important Emperors

Roman emperors ruled one of the largest and most influential states of the ancient world for centuries, but the office of “emperor” was never as simple as a hereditary crown. Some rulers inherited power, some were adopted, some were chosen by armies and others seized control through civil war.

The system began with Augustus, who carefully avoided calling himself king. Over time, imperial authority became more openly monarchical, military and court-centered. By late antiquity, the Roman state had multiple emperors, separate eastern and western courts and a political system very different from the one Augustus had created.

This guide follows the major dynasties and rulers of imperial Rome. For the larger political story, start with our rise and fall of the Roman Empire or browse the Ancient Rome hub.

Who was the first Roman emperor?

Augustus is conventionally regarded as the first Roman emperor. Born Gaius Octavius, he became Julius Caesar’s adopted heir and defeated his rivals in the civil wars that followed Caesar’s assassination.

In 27 BCE the Senate granted him the title Augustus. Rather than abolish republican institutions, he accumulated military command, tribunician authority, prestige and control over key provinces. This political system is usually called the Principate.

Augustus ruled until 14 CE and created a model that later emperors adapted rather than simply copied.

How did Roman emperors gain power?

There was no single constitutional rule of succession. Roman emperors came to power in several ways:

• Family succession: rulers could promote sons, stepsons or other relatives.
• Adoption: an emperor could formally adopt an adult successor.
• Military support: armies often played a decisive role in proclaiming emperors.
• Senatorial recognition: the Senate could formally recognize a ruler, though its independence varied greatly.
• Civil war: several emperors gained power by defeating rivals.

Because Rome lacked a fixed succession law, the death of an emperor could produce stability—or a violent struggle for control.

The Julio-Claudian emperors

The first imperial dynasty ruled from 27 BCE to 68 CE. It connected the families of Julius Caesar, Augustus, the Claudii and the descendants of Augustus’s wife Livia.

Augustus (27 BCE–14 CE)

Augustus ended the civil wars, reorganized the army, stabilized provincial administration and created the political structure of the Principate.

His reign also transformed Rome’s public image through building programs, religious restoration and carefully managed political symbolism.

Tiberius (14–37)

Tiberius was Augustus’s stepson and adopted heir. He was an experienced general and inherited a stable imperial system.

His relationship with the Senate deteriorated over time, and the later years of his reign became associated with treason trials and the influence of the Praetorian prefect Sejanus.

Caligula (37–41)

Gaius, better known by the childhood nickname Caligula, became emperor after Tiberius.

Ancient literary sources portray him as cruel, extravagant and unstable, but those accounts were written by elite authors hostile to his rule and need to be treated critically.

Caligula was assassinated by members of the Praetorian Guard in 41.

Claudius (41–54)

Claudius was proclaimed emperor after Caligula’s assassination. Despite being underestimated by some contemporaries, his government expanded imperial administration and completed major public works.

His most famous military achievement was the conquest of Britain beginning in 43 CE. That expansion is explored in our guide to Roman Britain.

Nero (54–68)

Nero became emperor as a teenager. His early government was influenced by advisers including Seneca and Burrus, but his reign later became associated with court conflict, executions and growing political opposition.

He is famously connected with the Great Fire of Rome in 64 CE, although the claim that he deliberately burned the city is not supported by reliable evidence.

Revolts in the provinces and the loss of military support forced Nero from power in 68. His death ended the Julio-Claudian dynasty.

The Year of the Four Emperors

Nero’s death exposed the weakness of Roman succession. In 69 CE, four emperors claimed power in rapid succession: Galba, Otho, Vitellius and Vespasian.

The struggle demonstrated a lasting political reality: armies stationed far from Rome could decide who became emperor.

Vespasian ultimately won the civil war and founded the Flavian dynasty.

The Flavian emperors

Vespasian (69–79)

Vespasian restored political stability after the civil war of 69. He improved imperial finances and began major construction projects, including the amphitheater later known as the Colosseum.

His rise also showed that an emperor did not need to come from Rome’s oldest aristocratic families.

Titus (79–81)

Titus had commanded Roman forces during the Jewish revolt and oversaw the capture of Jerusalem in 70 CE before becoming emperor.

His short reign coincided with major disasters, including the eruption of Mount Vesuvius in 79 and a serious fire in Rome.

Domitian (81–96)

Domitian strengthened imperial administration and frontier defense but had an increasingly hostile relationship with members of the Senate.

He was assassinated in a palace conspiracy in 96. The Senate condemned his memory, contributing to the strongly negative portrayal found in some ancient sources.

Nerva and the so-called Five Good Emperors

The period from Nerva to Marcus Aurelius is traditionally remembered as one of relative stability and effective imperial government. The label “Five Good Emperors” is a later historical judgment rather than a Roman political category.

Nerva (96–98)

Nerva was an elderly senator chosen after Domitian’s assassination. His rule was brief and politically fragile.

He adopted the successful general Trajan as his heir, establishing a succession that avoided immediate civil war.

Trajan (98–117)

Trajan was one of Rome’s most successful military emperors. Under him, the empire reached its greatest territorial extent, conventionally dated to 117 CE.

He conquered Dacia and launched major campaigns against the Parthian Empire. The wealth generated by conquest helped fund public works, including Trajan’s Forum and Column in Rome.

Hadrian (117–138)

Hadrian abandoned some of Trajan’s eastern conquests and focused more heavily on consolidating and defending existing imperial territory.

He traveled extensively through the provinces and is closely associated with frontier works such as Hadrian’s Wall in Britain.

His reign demonstrates that Roman emperors did not always measure success through continuous territorial expansion.

Antoninus Pius (138–161)

Antoninus Pius ruled during a comparatively peaceful period. His long reign was marked more by administration and legal activity than major conquest.

He rarely left Italy, governing through the imperial bureaucracy and provincial governors.

Marcus Aurelius (161–180)

Marcus Aurelius is remembered both as an emperor and as a Stoic philosopher, especially through his work commonly called the Meditations.

His reign was far from peaceful. Rome fought the Parthian Empire and faced repeated warfare along the Danube frontier. The Antonine Plague also struck the Roman world during this period.

Commodus and the end of the Antonine age

Marcus Aurelius was succeeded by his biological son Commodus, ending the sequence of adoptive succession that had characterized several earlier emperors.

Commodus increasingly presented himself through extravagant imperial imagery and identified strongly with Hercules. Relations with sections of the elite deteriorated badly.

He was assassinated in 192, triggering another succession crisis.

The Year of the Five Emperors

In 193 CE, several men competed for imperial power after Commodus’s death.

Pertinax ruled briefly before being murdered by the Praetorian Guard. Didius Julianus then acquired the throne in a notorious political auction conducted by the Guard.

Provincial armies proclaimed rival commanders. Septimius Severus ultimately defeated his competitors and founded the Severan dynasty.

The Severan dynasty

Septimius Severus (193–211)

Septimius Severus came from Lepcis Magna in Roman North Africa. He relied heavily on military support and increased soldiers’ pay and privileges.

His reign strengthened the political importance of the army and further changed the balance between emperor, Senate and military.

Caracalla (198–217)

Caracalla ruled jointly with his father and later with his brother Geta. After Severus’s death, Caracalla had Geta killed and ruled alone.

His most famous measure was the Constitutio Antoniniana of 212, which granted Roman citizenship to most free inhabitants of the empire.

Elagabalus (218–222)

Elagabalus came to power as a teenager and became associated in hostile ancient sources with religious innovation and court scandal.

He promoted the Syrian sun god Elagabal in Rome and alienated important political and military groups. He was killed by the Praetorian Guard.

Severus Alexander (222–235)

Severus Alexander was the last emperor of the Severan dynasty. His death at the hands of his own troops in 235 conventionally marks the beginning of the Crisis of the Third Century.

The Crisis of the Third Century

From 235 to 284, Rome experienced rapid imperial turnover, civil war, invasion, economic disruption and breakaway states.

Many emperors were proclaimed by armies and then killed after short reigns. The empire temporarily fragmented into competing political units.

The period demonstrates how closely imperial authority had become tied to military success.

Decius (249–251)

Decius attempted to strengthen Roman religious unity and required inhabitants of the empire to perform public sacrifice, producing a major persecution of Christians.

He died fighting Goths at the Battle of Abritus in 251, becoming the first Roman emperor known to have died in battle against an external enemy.

Valerian (253–260)

Valerian suffered one of the most humiliating defeats in Roman imperial history when he was captured alive by the Persian king Shapur I in 260.

Gallienus (253–268)

Gallienus ruled during severe military crisis and introduced important changes in army organization and command.

Aurelian (270–275)

Aurelian reunified much of the empire after defeating the Palmyrene and Gallic breakaway regimes.

His achievements earned him the title Restitutor Orbis, “Restorer of the World.”

Diocletian and the Tetrarchy

Diocletian came to power in 284 and introduced the most important restructuring of imperial government since Augustus.

He created the Tetrarchy, a system in which two senior emperors, called Augusti, ruled alongside two junior Caesars.

The idea was to improve frontier defense and create an orderly method of succession. Diocletian also reorganized taxation, provinces, military command and imperial ceremony.

The Tetrarchy did not survive intact after his retirement, but it permanently changed the structure of Roman government.

Constantine the Great

Constantine emerged from the civil wars that followed the Tetrarchy and became sole emperor.

His reign transformed the empire in several ways. He supported Christianity, founded Constantinople as an imperial capital and introduced major administrative and monetary reforms.

The Battle of the Milvian Bridge in 312 became closely associated with Constantine’s support for Christianity. In 313, the agreement usually called the Edict of Milan established religious toleration for Christians and others.

Constantine was baptized near the end of his life in 337.

The sons of Constantine

After Constantine’s death, his sons divided the empire and eventually fought among themselves.

This pattern—multiple emperors governing different regions while remaining part of one Roman imperial system—became increasingly common in late antiquity.

Julian (361–363)

Julian, later called “the Apostate” by Christian writers, attempted to restore and reorganize traditional Roman religious practices after decades of increasing imperial support for Christianity.

His reign was brief. He died during a campaign against the Persian Empire in 363.

Valentinian and Valens

Valentinian I ruled in the West while his brother Valens governed the East.

Valens was killed at the Battle of Adrianople in 378 during fighting against Gothic forces. The defeat became one of the major military shocks of the late Roman period.

Theodosius I

Theodosius I ruled the entire Roman Empire briefly before his death in 395.

His reign was crucial to the Christianization of imperial government, and Nicene Christianity became increasingly privileged by the state.

After his death, his sons Arcadius and Honorius ruled the eastern and western courts separately.

Western emperors in the fifth century

The fifth-century Western Empire faced increasing territorial loss, fiscal weakness and political instability.

Honorius (395–423)

Honorius ruled during major crises including the Gothic sack of Rome in 410 and the collapse of regular Roman administration in Britain.

Valentinian III (425–455)

Valentinian III’s long reign depended heavily on powerful generals, especially Aetius.

Aetius helped coordinate Roman and allied resistance to Attila the Hun in Gaul in 451. Valentinian later killed Aetius personally and was himself assassinated the following year.

Majorian (457–461)

Majorian is often regarded as one of the last Western emperors to make a serious attempt to restore central authority.

He campaigned in Gaul and Spain and planned a major expedition against the Vandals in North Africa. After the fleet was destroyed, his political position collapsed and the general Ricimer had him removed.

Who was the last Roman emperor in the West?

Romulus Augustulus is conventionally described as the last Western Roman emperor. He was placed on the throne by his father Orestes in 475 and deposed by Odoacer in 476.

However, Julius Nepos—whom Orestes had driven from Italy—continued to claim the Western imperial title from Dalmatia until his death in 480.

The question therefore depends on whether “last emperor” means the final ruler in Italy or the final internationally recognized Western claimant.

For the broader collapse, see Why Did the Roman Empire Fall?.

What happened to the Eastern Roman emperors?

Imperial rule did not end in 476. Emperors continued to rule from Constantinople for centuries.

Modern historians usually call this state the Byzantine Empire, but its inhabitants continued to identify themselves as Romans.

Emperors such as Justinian I later reconquered substantial western territories. The eastern Roman imperial line ultimately ended only when Constantinople fell to the Ottoman Empire in 1453.

Major Roman emperors timeline

• 27 BCE–14 CE — Augustus: establishes the Principate.
• 14–37 — Tiberius: consolidates the Augustan system.
• 41–54 — Claudius: conquest of Britain begins.
• 54–68 — Nero: last Julio-Claudian emperor.
• 69–79 — Vespasian: restores stability after civil war.
• 98–117 — Trajan: empire reaches greatest territorial extent.
• 117–138 — Hadrian: consolidates frontiers.
• 161–180 — Marcus Aurelius: philosopher emperor and frontier commander.
• 193–211 — Septimius Severus: strengthens military monarchy.
• 284–305 — Diocletian: creates the Tetrarchy.
• 306–337 — Constantine: supports Christianity and establishes Constantinople.
• 379–395 — Theodosius I: last emperor to rule both East and West together.
• 475–476 — Romulus Augustulus: final emperor ruling in Italy.

Which Roman emperor was the most powerful?

There is no objective single answer because “powerful” can mean military success, territorial extent, political control or long-term influence.

Augustus created the imperial system. Trajan ruled the empire at its greatest extent. Diocletian reshaped late Roman government. Constantine permanently changed the political and religious direction of the empire.

Each exercised power in a different Roman political system.

Were all Roman emperors dictators?

Roman imperial government concentrated enormous authority in one ruler, but the exact structure changed over time.

Augustus deliberately framed his position through republican offices and titles. Later emperors increasingly used court ceremony and openly monarchical language.

Some emperors ruled with the cooperation of the Senate and established elites, while others relied more heavily on military coercion. The office itself evolved significantly between Augustus and late antiquity.

How many Roman emperors were there?

The answer depends on how historians count disputed rulers, co-emperors, usurpers and eastern emperors after 476.

There is no single universally accepted total. Roman history included many periods when several men claimed imperial authority at the same time.

Roman emperors FAQ

Who was the first Roman emperor?

Augustus, who ruled from 27 BCE to 14 CE, is conventionally regarded as the first Roman emperor.

Who was emperor when Jesus was born?

Augustus ruled during the period traditionally associated with the birth of Jesus.

Who was emperor when Jesus was crucified?

Tiberius was emperor during the governorship of Pontius Pilate in Judaea.

Which emperor conquered Britain?

Claudius launched the Roman conquest of Britain in 43 CE, although conquest and resistance continued for decades.

Which emperor built the Colosseum?

Construction began under Vespasian and the amphitheater was inaugurated under his son Titus. Domitian later completed additional work.

Which emperor built Hadrian’s Wall?

Hadrian ordered the frontier system built across northern Britain beginning in 122 CE.

Who was the last Western Roman emperor?

Romulus Augustulus is the conventional answer because he was deposed in Italy in 476. Julius Nepos continued to claim the title until 480.

Sources and further reading

• Suetonius, The Twelve Caesars.
• Cassius Dio, Roman History.
• Herodian, History of the Roman Empire.
• Anthony Birley, Marcus Aurelius.
• Pat Southern, The Roman Empire from Severus to Constantine.
• David S. Potter, The Roman Empire at Bay.
• Encyclopaedia Britannica — List of Roman emperors
• The Metropolitan Museum of Art — Roman imperial history