Who Was Constantine the Great and What Did He Accomplish?

Constantine the Great was one of the most important Roman emperors whose policies and choices reshaped not only the Roman Empire but also our world.

Dec 7, 2022By Vedran Bileta, MA in Late Antique, Byzantine, and Early Modern History, BA in History

who was constantine the great


Without a doubt, Constantine the Great is one of the most influential Roman emperors. He came to power in the pivotal moment for the empire, after winning a decades-long civil war. As the sole ruler of the Roman Empire, Constantine I personally oversaw the major monetary, military and administrative reforms, laying the foundation for the strong and stable fourth-century state. By leaving the Roman Empire to his three sons, he established a powerful imperial dynasty. Constantine the Great is, however, best known for accepting Christianity, a watershed moment that led to rapid Christianization of the Roman Empire, changing not only the fate of the Empire but of the entire world. Lastly, by moving the imperial capital to the newly founded Constantinople, Constantine the Great ensured the Empire’s survival in the East, centuries after the fall of Rome.


Constantine the Great Was a Son of the Roman Emperor

constantine marble bust
Marble portrait of the Emperor Constantine I, c. AD 325-70, Metropolitan Museum, New York


Flavius Valerius Constantius, future emperor Constantine the Great, was born in 272 CE in the Roman province of Upper Moesia (present-day Serbia). His father, Constantius Chlorus, was a member of Aurelian’s bodyguard, who later became emperor in the Tetrarchy of Diocletian. By dividing the Roman Empire between the four rulers, Diocletian hoped to avoid civil wars that plagued the state during the Third Century Crisis. Diocletian peacefully abdicated, but his system was doomed to fail. Following Constantius’ death in 306, his troops immediately proclaimed Constantine emperor, clearly violating the meritocratic Tetrarchy. What followed was the two-decade-long civil war.


He Won the Crucial Battle at the Milvian Bridge

battle of milvain bridge painting by romano vatican
The Battle of the Milvian Bridge, by Giulio Romano, Vatican City, via Wikimedia Commons


The decisive moment in the civil war came in 312 CE, when Constantine I defeated his rival, emperor Maxentius, at the Battle of the Milvian Bridge outside Rome. Constantine was now in full control of the Roman West. But, more importantly, the victory over Maxentius marked a crucial threshold in the Roman Empire’s history. Apparently, prior to the battle, Constantine saw a cross in the sky and was told: “In this sign shall you conquer.” Encouraged by the vision, Constantine ordered his troops to paint their shield with the chi-rho emblem (initials symbolizing Christ). The Arch of Constantine, built to commemorate the victory over Maxentius, still stands in the center of Rome. 


Constantine the Great Made Christianity the Official Religion

constantine and sol invictus
Coin featuring Constantine and Sol Invictus, 316 AD, via the British Museum, London

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Following his triumph, in 313 CE, Constantine and his co-emperor Licinius (who ruled the Roman East) issued the Edict of Milan, declaring Christianity one of the official imperial religions. Direct imperial support laid the strong foundation for the Christianization of the Empire and, eventually, the world. It is hard to say if Constantine was a true convert or an opportunist who saw the new religion as a possibility to bolster his political legitimacy. After all, Constantine played an essential role at the Council of Nicaea, which laid down the principles of Christian belief – the Nicene Creed. Constantine the Great could also see Christian God as a reflection of Sol Invictus, an oriental deity and patron of the soldiers, introduced into the Roman pantheon by soldier-emperor Aurelian.


Emperor Constantine I Was a Great Reformer

bronze late roman horseman
Late Roman bronze horseman, ca. 4th century CE, via Museu de Guissona Eduard Camps i Cava


In 325 CE, Constantine defeated his last rival, Licinius, becoming the sole master of the Roman world. Finally, the emperor could push major reforms to reorganize and strengthen the beleaguered Empire and earn his sobriquet of “the Great.” Building upon Diocletian’s reforms, Constantine reorganized the imperial military into frontier guards (limitanei), and a smaller but mobile field army (comitatensis), with elite units (palatini). The old Praetorian Guard fought against him in Italy, so Constantine dissolved them. The new army proved efficient in one of the last imperial conquests, the brief takeover of the Dacia. To pay his troops and strengthen the Empire’s economy, Constantine the Great strengthened the imperial coinage, introducing the new gold standard – solidus – which contained 4.5 grams of (almost) solid gold. Solidus would retain its value until the eleventh century. 


Constantinople – The New Imperial Capital

ideal reconstruction of constantinople
Reconstruction of Constantinople in the year 1200, via Vivid Maps


One of the most far-reaching decisions made by Constantine was the foundation of Constantinople (what was Constantinople) in 324 CE – the new capital of the rapidly Christianizing Empire. Unlike Rome, the city of Constantine was easily defensible due to its prime geographic location and well-protected harbors. It was also close to the imperiled frontier zones on the Danube and the East, allowing for a faster military response. Lastly, being located at the crossroads of Europe and Asia and on the terminus of the famed Silk Roads meant that the city quickly became an incredibly wealthy and thriving metropolis. After the fall of the Roman West, Constantinople remained the imperial capital for more than a thousand years.


Constantine the Great Established the New Imperial Dynasty

emperor constantine medallion
A gold medallion of Constantine I, with Constantine (centre) crowned by the manus Dei (hand of God), his eldest son, Constantine II, is to the right, whilst Constans and Constantius II are to his left, from the Szilágysomlyo Treasure, Hungary, photo by Burkhard Mücke,


Unlike his mother, Helena, a staunch Christian and one of the first pilgrims, the emperor took the baptism only on his deathbed. Soon after his conversion, Constantine the Great died and was buried in the Church of Holy Apostles in Constantinople. The emperor left the Roman Empire to his three sons – Constantius II, Constantine II and Constans – thus establishing the powerful imperial dynasty. His successors did wait long to plunge the Empire into another civil war. However, the Empire reformed and strengthened by Constantine endured. The last emperor of the Constantinian dynasty – Julian the Apostate – embarked on the ambitious but ill-fated Persian campaign. More importantly, Constantine’s city – Constantinople – ensured the survival of the Roman Empire (or the Byzantine Empire) and Christianity, his lasting legacy, in the following centuries.

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By Vedran BiletaMA in Late Antique, Byzantine, and Early Modern History, BA in HistoryVedran is a doctoral researcher, based in Budapest. His main interest is Ancient History, in particular the Late Roman period. When not spending time with the military elites of the Late Roman West, he is sharing his passion for history with those willing to listen. In his free time, Vedran is wargaming and discussing Star Trek.