The division of the Roman Empire refers to the gradual and eventually permanent separation of the empire into two distinct halves, the Western Roman Empire and the Eastern Roman Empire, a process that unfolded over more than a century from the reign of Emperor Diocletian in the 280s CE to the final formal division upon the death of Emperor Theodosius I in 395 CE. The division was a response to the enormous size of the empire and the difficulty of governing and defending it from a single center. It had profound consequences for world history, as the two halves developed very differently, with the Western Empire collapsing in 476 CE while the Eastern Empire, later known as the Byzantine Empire, survived for nearly another thousand years.
WHAT WAS ANCIENT ROME?
Ancient Rome was one of the most powerful civilizations in world history. It began as a small city-state on the Italian peninsula and grew over many centuries into a vast empire that stretched from Britain in the northwest to Egypt in the southeast. At its height, the Roman Empire controlled much of Europe, North Africa, and parts of the Middle East, governing an estimated 70 million people. The division of this enormous empire was one of the most significant turning points in its long history, and understanding it helps explain both the fall of the Western Roman Empire and the survival of the Eastern Roman world for centuries afterward.
DIVISION OF THE ROMAN EMPIRE – BACKGROUND AND THE CRISIS OF THE THIRD CENTURY
To understand why the empire was divided, it is necessary to understand the deep crisis that Roman governance faced in the third century CE. The period from 235 to 284 CE is known to historians as the Crisis of the Third Century. During these roughly fifty years, the empire experienced more than fifty different emperors, most of whom died violently. At the same time, the empire was attacked from multiple directions: Germanic tribes pressed in from the north and west along the Rhine and Danube rivers, while the newly powerful Sassanid Persian Empire launched repeated invasions from the east. Regions of the empire temporarily broke away and declared their own rulers. Trade declined, disease spread, and the currency lost much of its value. The empire came close to total collapse.
Several emperors in the later third century managed to stabilize the situation temporarily, but it was Diocletian, who came to power in 284 CE, who introduced the most far-reaching solution.
DIVISION OF THE ROMAN EMPIRE – DIOCLETIAN AND THE TETRARCHY
Diocletian ruled from 284 to 305 CE and is widely regarded as one of the most capable administrators in Roman history. He recognized that the empire had grown too large and its problems too complex for a single ruler to manage effectively. His solution was a system known as the Tetrarchy, meaning rule by four, which he established in 293 CE.
Under the Tetrarchy, the empire was divided into two administrative halves, each governed by a senior emperor called an Augustus and a junior emperor called a Caesar. Diocletian himself served as the senior Augustus of the Eastern half, based at Nicomedia in modern-day Turkey. His colleague Maximianus served as the Augustus of the Western half, based at Milan in northern Italy rather than Rome, which was too far from the frontiers. Two junior Caesars, Galerius in the east and Constantius in the west, assisted them. Each tetrarch was responsible for governing and defending his portion of the empire. The intention was that each Caesar would eventually succeed his Augustus, creating an orderly succession and avoiding the civil wars that had plagued the empire for decades.
Diocletian also carried out sweeping administrative reforms, creating new smaller provinces to make government more manageable, separating military command from civilian administration, and reorganizing the army. He overhauled the tax system and attempted to control inflation through the Edict on Maximum Prices in 301 CE, which set price ceilings for hundreds of goods and services across the empire. He also launched the last major persecution of Christians in the Roman Empire, the Great Persecution beginning in 303 CE. In 305 CE, Diocletian became the first Roman emperor to voluntarily abdicate, retiring to his palace in Spalatum on the Adriatic coast, in what is now Split in modern-day Croatia.
DIVISION OF THE ROMAN EMPIRE – CONSTANTINE AND CONSTANTINOPLE
After Diocletian’s abdication, the Tetrarchy quickly broke down. The intended system of orderly succession collapsed into civil wars as multiple claimants fought for control. After more than a decade of conflict, Constantine, the son of the western Caesar Constantius, emerged as the dominant figure. He defeated his final rival Licinius in 324 CE and reunited the empire under his sole rule.
Constantine’s most consequential decision was the founding of a new imperial capital in the east. In 330 CE, he established the city of Constantinople on the site of the Greek city of Byzantium, at the strategic crossing point between Europe and Asia on the Bosphorus strait. Constantinople was ideally located for the defense of the eastern frontier and access to the wealthy provinces of the east. Constantine built the city on a grand scale, filling it with monuments, public buildings, churches, and a new Senate. He declared it the New Rome.
Constantine also issued the Edict of Milan in 313 CE, granting religious tolerance to Christians throughout the empire, and became the first Roman emperor to convert to Christianity, a conversion that would have enormous consequences for both the empire and for world history. The founding of Constantinople shifted the center of gravity of the empire decisively eastward and reinforced the growing divide between the two halves.
DIVISION OF THE ROMAN EMPIRE – THE FINAL DIVISION IN 395 CE
After Constantine’s death, the empire was divided and reunited several times among his successors. The last ruler to govern a truly unified Roman Empire was Theodosius I, who came to power in 379 CE. Theodosius made Christianity the official state religion of the empire in 380 CE, formally ending the legal practice of traditional Roman polytheism. He also temporarily reunited the two halves after military conflicts in the west.
When Theodosius I died on January 17th, 395 CE, he divided the empire between his two sons. His older son Arcadius, aged about eighteen, received the Eastern Empire with its capital at Constantinople. His younger son Honorius, aged ten, received the Western Empire, initially governed in practice by the general Stilicho who served as regent. This division of 395 CE proved to be permanent. The empire was never reunited again.
DIVISION OF THE ROMAN EMPIRE – EAST AND WEST: A GROWING CONTRAST
The two halves of the empire had always been somewhat different in character, and after the final division those differences grew more pronounced. The Eastern Empire was significantly wealthier. Its provinces included Egypt, Syria, and Asia Minor, which were among the most economically productive regions of the ancient world. Its cities, particularly Constantinople, Alexandria, and Antioch, were large, prosperous, and densely populated. The Eastern Empire’s position at the crossroads of trade routes connecting the Mediterranean to Asia gave it access to enormous commercial wealth. It was also more defensible, since Constantinople sat on a peninsula that could be protected by relatively small forces and was never successfully besieged until 1204 CE.
The Western Empire was weaker in almost every comparable respect. Its most economically productive provinces, particularly North Africa and Spain, were far from its center and increasingly difficult to defend. The Rhine and Danube frontiers required constant military attention and enormous expense. The population of the west was smaller and its economy less developed. The city of Rome itself, while still enormously prestigious, was increasingly impractical as a military and administrative capital, and western emperors often governed from Milan or Ravenna, which were closer to the threatened frontiers.
These differences meant that when Germanic peoples began pressing more intensively on the western frontiers in the late fourth and fifth centuries, the Western Empire had far less capacity to resist them than the Eastern Empire had to defend its own borders.
DIVISION OF THE ROMAN EMPIRE – CONSEQUENCES AND THE FALL OF THE WEST
After the final division of 395 CE, the Western Empire deteriorated rapidly. The Visigoths under King Alaric sacked the city of Rome itself in 410 CE, the first time in 800 years that Rome had fallen to an enemy, and the shock spread across the entire Mediterranean world. The Vandals crossed from Spain into North Africa and captured Carthage in 439 CE, cutting off the grain supply that the Western Empire depended on. Britain was effectively abandoned by Roman forces around 410 CE. Attila the Hun devastated large areas of Gaul and Italy in the 440s and 450s CE. By the 460s, the Western emperors controlled little real territory and commanded little real authority. Germanic leaders held the actual military power.
The final end came on September 4th, 476 CE, when the Germanic chieftain Odoacer deposed the last Western Roman Emperor, Romulus Augustulus, a sixteen-year-old boy. Odoacer sent the imperial regalia to Constantinople and declared himself king of Italy rather than emperor of Rome. The Western Roman Empire was over.
DIVISION OF THE ROMAN EMPIRE – THE EASTERN EMPIRE SURVIVES
The Eastern Roman Empire, which later historians call the Byzantine Empire, survived for nearly another thousand years. It continued to call itself the Roman Empire and its people called themselves Romans. It maintained Roman law, Roman administrative traditions, and the Christian faith that had become central to Roman identity under Constantine and Theodosius. It also maintained the Greek language, which gradually replaced Latin as the language of government in the east.
The Eastern Empire reached another high point under Emperor Justinian I, who ruled from 527 to 565 CE and temporarily reconquered parts of the Western Empire, including North Africa and Italy. He also produced the great legal compilation known as the Corpus Juris Civilis, which became the foundation of European civil law. The Byzantine Empire survived subsequent challenges from Arab expansion in the seventh century, Bulgarian invasions in the ninth and tenth centuries, and the First Crusade in the eleventh century, finally falling only when the Ottoman Turks under Sultan Mehmed II captured Constantinople on May 29th, 1453 CE.
SIGNIFICANCE OF THE DIVISION OF THE ROMAN EMPIRE
The division of the Roman Empire was one of the most important turning points in world history. It set in motion the events that led to the fall of the Western Empire and the beginning of the Middle Ages in Europe. The two halves of the divided empire followed very different paths, with the east preserving and transmitting classical learning, Roman law, and Christian theology through the Byzantine Empire, while the west was reshaped by Germanic kingdoms that eventually became the nations of medieval Europe.
The division also contributed to one of the deepest and most lasting splits in Christian history. The church of the Eastern Empire, centered on Constantinople, and the church of the Western Empire, centered on Rome, developed differently in language, theology, and practice over the following centuries, eventually producing the formal split between the Roman Catholic and Eastern Orthodox churches in 1054 CE. The effects of the division of the Roman Empire are still visible in the political, religious, and cultural geography of Europe and the Mediterranean world today.
