Only one Roman emperor is called ‘the Great’, and that emperor is Constantine. Today we mostly associate Constantine with the Christianisation of his empire, yet even if he had remained steadfastly pagan, Constantine would still deserve his title. Few men have had such a dramatic and lasting effect upon the destiny of an entire continent. Constantine came to power when the fate of Rome hung in the balance. The efforts of his predecessors had pulled Rome out of the desperate struggle for survival, which today we call the Third Century Crisis. However, if the worst was over, the battle was far from won. It would fall to Constantine to stabilise the new world order that became known as Late Antiquity.


Although the deeds of Constantine were exhaustively documented by contemporary historians, the man himself remains an enigma. Few of Constantine’s biographers have been unbiased. Early Christian writers portrayed Constantine as wise and benevolent. There was a backlash against this in the early modern era, when Constantine was depicted as a vicious, backstabbing political opportunist who slaughtered allies and family alike in a ruthless struggle for power. These historians even saw a cynical political ploy in Constantine’s embrace of Christianity – a religion he took to late and imperfectly understood.

Who was Constantine the Great?

Constantine was born in AD 272 in the Roman province of Upper Moesia, in modern Serbia. When he was 21 years old, his father Constantius, a successful administrator and general, was made Caesar in the Tetrarchy of Diocletian. As part of that dynastic arrangement, Constantius had to put aside Constantine’s mother Helena and marry Theodora, daughter of the emperor Maximian.

Bust of Constantine the Great
Once he gained control of the entire Roman Empire, Constantine set about an ambitious programme of reform. (Photo by Getty Images)

In AD 305, Constantius became co-emperor with a man called Galerius. Constantine had previously been a competent subordinate of Galerius, but now became a hostage for his father’s good behaviour. When given grudging permission to join Constantius on campaign in Britain, Constantine fled to his father’s side. He was there when Constantius died in AD 306, in Eboracum - the city of York in modern England. Constantine’s troops immediately proclaimed him as Caesar, though this violated the more meritocratic Tetrarchic system. Constantine went on to legitimise his standing in the eyes of his army by defeating a Frankish invasion of Gaul. The Frankish leaders were captured and, in an unprecedented display of savagery, their two kings were thrown to the beasts in the arena.

Constantine’s usurpation of the title of Caesar left no place in the tetrarchy for Maxentius, the son of the former emperor Maximian. Consequently, Maximian himself came out of retirement and attempted to seize control of Constantine’s army. The coup failed and Maximian committed suicide.

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By AD 311, Constantine was in control of the west and a new emperor called Licinius ruled the east. In the meantime, Maxentius had seized control of Italy. While his advisers – and even his soothsayers – felt that Maxentius was too strongly entrenched, Constantine marched against him anyway. Maxentius had the larger army and came out of Rome to challenge Constantine at the Milvian bridge.

What was the tetrarchy and how did it work?

In AD 293, the emperor Diocletian proposed to end the empire’s constant dynastic struggles by creating a career path to the imperial throne. In this system there were to be two senior emperors – Augusti – who commanded the eastern and western parts of the empire.

Each Augustus had an understudy called a Caesar, who replaced him when he died or retired. The system was still in its youth when it was ignored by Constantine’s troops who proclaimed him emperor, despite Constantine having no claim to that rank under the tetrarchic system.

Here, for the first time, the army of Constantine carried the labarum, a banner inscribed with the superimposed Greek letters X (chi) and P (rho). Together these read ‘Chr[ist]’. According to later texts, the Saviour himself told Constantine in a dream to construct this banner and to place the chi-rho emblem on the shields of his soldiers. Either divine intervention or bad generalship by Maxentius gave a quick victory to Constantine.

Therefore it seems ungrateful that there are no Christian symbols on the arch that stands beside the Colosseum in Rome commemorating Constantine’s victory. However, that monument was commissioned by the resolutely pagan senate – and is constructed mostly of materials recycled from the reigns of Hadrian and Trajan.

Constantine and Christianity

Supreme in the west, Constantine turned his malevolent attention upon his co-emperor in the east. The two emperors had previously co-operated amiably. Licinius had married Constantine’s half-sister Constantia, and the pair thrashed out their differences in a meeting in Milan in AD 313 – a summit famous for the so-called ‘Edict of Milan’. This is often misunderstood as the ‘edict’ that made the empire Christian, though it actually did nothing of the sort. There may not have even been an official pronouncement, but merely mutual agreement that, as the contemporary writer Lactantius says, “everyone be given the freedom to worship as he wishes, and nothing detract from the dignity of any religion”.

That said, Constantine was now a promoter of Christianity (he had earlier been a worshipper of Sol, the Unconquered Sun). As relations between the two emperors deteriorated, Licinius allegedly began to discriminate against Christians. This was either deliberate provocation, or largely fake news propagated by Constantine to legitimise his aggression in the civil war, which began in AD 320. Both sides considered the war a struggle between the old pagan values and upsurgent Christianity.

In battle after battle, though often outnumbered, the Christians carried their sacred labarum to victory. Eventually Licinius surrendered on condition that his life be spared. Constantine agreed, but once Licinius had become a private citizen, Constantine had him arrested and executed. While he was about it, Constantine also disposed of his nephew, Licinius’ son.

The Arch of Constantine in Rome
The Arch of Constantine in Rome salutes the victory over Maxentius. (Photo by Getty Images)

Constantine was now free to shape the empire however he wanted. There was much to be done. Rome’s frontiers everywhere were under threat, the administration was disorganised, and the economy was still a mess. Violent religious disagreements – often the visible face of deeper social rifts – convulsed Roman society. Constantine had to start earning his sobriquet of ‘the Great’.

Constantine began by banning Christians from taking part in the (pagan) state religion – not that Christians wanted to, but the ban eased tensions over Christian non-participation. Constantine wanted social harmony, and this meant enforcing religious harmony. He tried to establish conformity between the wildly different forms of contemporary Christian belief, notably by calling a council of bishops to the eastern city of Nicaea. There the basic principles of Christianity were thrashed out in a statement known today as the Nicene Creed. This doctrine remains fundamental to Christian liturgies today.

As emperor, Constantine was in the ambiguous position of simultaneously being a keen promoter of Christianity and the official head of the state’s pagan religions. He used this situation to his advantage; temples of the state religion were declared to be imperial property.

For more than a millennium, gold and silver that would have otherwise circulated through the imperial economy had been slowly converted to dedicatory offerings by the pious and locked away in temple storerooms. Meanwhile, starved of coinage, imperial mints had churned out ever more debased currency, leading to rampant inflation.

Constantine unsentimentally turned over these temple treasures to be minted into hard cash. His main coin was the solidus, 4.5 grams of (almost) solid gold. There were 72 solidi to the Roman pound (Libra) and thereafter currency was measured in librae, solidi and denarii. These later became pounds, shillings and pence (£.s.d.) and even today the pound sign is a stylized letter ‘L’. Soldiers are so called because they take the ‘Queen’s shilling’ (solidus reginae).

Organising the empire

Constantine was very aware that the main threat to his life came from his own army. Over the previous century, more emperors had died in military coups than from any other cause. In fact, of recent emperors, only Constantius, Claudius Gothicus (plague) and Diocletian had died naturally. To maximise his chances of dying in bed, Constantine made several changes.

Firstly, he slowed the trend of giving provincial governorships to non-senators. Instead he turned the process on its head, cleverly making senators of provincial governors, thus retaining capable subordinates but gaining a loyal senate. However, Constantine kept senators from military command, as this might have proved too tempting for the overly ambitious.

In military affairs, Constantine built upon the reforms of his predecessor Diocletian. Even as a more flexible military style evolved to combat new and more sophisticated enemies, legionary armour became both lighter and simpler. This was partly because many detachments now operated far from legion bases capable of maintaining and repairing complex armour, and partly because Constantine’s army relied more on heavy cavalry.

The old Praetorian Guard had fought against him in Italy, so Constantine disbanded this unit. His army began the gradual separation into frontier guards (limitanei) and a field army of comitatensis with elite units called the palatini. More barbarian units were recruited, which fought under their own commanders in their traditional style.

Thanks to his successful early campaigns in the west, Constantine could focus on securing the east. The Dacia region had earlier been abandoned due to a shortage of troops to defend it, but Constantine aimed to wrench this lost province from the hands of the occupying Goths.

He first allied with the nearby Sarmatian tribe and, when the Goths submitted after taking heavy casualties, then turned on his Sarmatian allies and beat them into surrender too. While he failed to regain all of Dacia, he succeeded to the extent that the modern country is called Romania, and the native language is recognisably Latin-based. Constantine also planned a major campaign against the Persians. Though his sickness and death led to the cancellation of this attack, knowledge of the preparations kept the Persians carefully non-provocative.

When did Constantine become Christian?

Like many Roman emperors, Constantine’s domestic life was worthy of a good soap opera. His mother was a saint. Literally. Saint Helena of Constantinople embarked on a highly publicised pilgrimage to the Holy Land, founding churches as she went along. One such church was – according to a nearcontemporary writer Socrates Scholasticus – founded on the site of the Holy Sepulchre, leading to the discovery of the True Cross, on which Jesus was crucified. Helena died in AD 330 and her magnificent sarcophagus is now in the Vatican museum.

Helena’s death was probably hastened by anguish at the execution of her grandson Crispus. Crispus was the son of Constantine and the otherwise unknown Minervina, who was either his first wife or a concubine. The subsequent relationship between Crispus and his later stepmother Fausta has, ever since, been the subject of lurid speculation.

Crispus fought with great distinction in the war against Licinius, and was widely assumed to be heir-apparent to the empire. Yet in AD 326, when Constantine was on his way to Rome to celebrate the 20th anniversary of his accession, Crispus was suddenly arrested on unspecified charges and promptly executed. All official record of Crispus was destroyed.

Relief depicting the Donation of Constantine
Constantine hands over significant territories to Pope Sylvester I. (Photo by Fine Art Images/Heritage Images/Getty Images)

The donation of Constantine

One of the reasons for the extraordinary power of the Church in medieval Europe was because Rome and most of western Europe ‘belonged’ to the Pope. In gratitude for being cured of leprosy by Pope Sylvester I, Constantine gave to the papacy Rome, Italy and all the western provinces. In his generosity, the emperor also handed the Pope estates elsewhere in the empire, and sovereignty over other sees (dioceses) of the Church in Constantinople, Alexandria, Jerusalem and Antioch.

The document recording this ‘donation’ was later shown to be a blatant forgery (it did not even get the dates right), but by then the bishops of Rome had gained a primacy which later Popes have never relinquished.

Later that year, Constantine’s wife Fausta was also executed. Were the pair illicit lovers? Did the two plot a coup together? Both theories have been proposed. It is notable that, in later years when they became emperors, the sons of Fausta never retracted the official condemnation of their mother.

In AD 324, Constantine founded a new, Christian capital for the empire. After considerable deliberation, he chose the existing city of Byzantium, a Greek colony founded in 650 BC. Unlike Rome, Byzantium was well situated strategically, being located near the military danger zones of the Danube and Syria. To say that Constantine’s ‘New Rome’ flourished is to put it mildly. After the fall of the Roman west, Byzantium – or Constantinople, as it became known – was the centre of imperial government for the next thousand years.

In the spring of AD 337, Constantine fell gravely ill. He had put off baptism until then, perhaps because being baptised in one form of Christianity would alienate followers of the others. (Despite Constantine’s efforts, the church was still riven with conflicting ideas, especially about the nature of Christ.)

In the end Constantine was baptised by a pro-Arian bishop; that is, one who believed that Jesus was separate from the Father and not part of a single Trinitarian being. Constantine first wished to be baptised in the River Jordan.

Then, as his condition deteriorated, he tried to return to Constantinople, but died on the journey. He was 65 years old. He was buried in the resting place he had carefully chosen in the Church of the Twelve Apostles. Today, after the ravaging of Constantinople by Crusader and Ottoman conquerors, the location of that church is unknown.

Constantine did not merely change the destiny of Europe. Without him, there wouldn’t be a ‘Europe’ as we know it today. For centuries, Roman civilisation was protected in the east by Constantinople, which stopped barbarian hordes from crossing the Bosporus. Then, in later years, Constantinople and the crumbling Byzantine Empire held back the Muslim armies, allowing Europe to slowly regain its population and economic strength. When Constantinople finally fell, the Ottoman armies thereafter advanced as far west as Vienna. Had Constantinople not held the line until 1453, the eastern invaders might well have entirely overrun Europe before then.

Secondly, until the Edict of Milan and Constantine’s unwavering support thereafter, there was no guarantee that Christianity would take hold in the west. Christianity was at one point just as strong in the Sassanian Persian empire, but has never been more than a minority religion in the region. Yet after the political disintegration of the west, Christianity was the intellectual and spiritual force which gave Europe its identity as ‘Christendom’. And it was an explicitly Christian coalition that eventually threw back the Ottoman Muslims at Vienna in 1683.

Philip Matyszak has written numerous books on the Roman Empire, including 24 Hours In Ancient Rome: A Day in the Life of the People Who Lived There


This content first appeared in the January 2019 issue of BBC History Revealed