Twenty-two years after the empire set out to destroy the Christian church, a Roman emperor summoned its bishops to a conference at his own expense and paid for their travel on the imperial post.
The previous lesson ended with Diocletian's succession scheme collapsing within eighteen months, and with the army at York proclaiming a dead emperor's son on 25 July 306. This lesson follows that son. Constantine's reign is where the reconstructed state of Diocletian acquires the two features that define the rest of Roman history: a capital in the east and a church inside the government.
From York to the Tiber
Constantine spent six years consolidating the north-western provinces while the tetrarchy tore itself apart, and in 312 he invaded Italy against Maxentius, who held Rome and Africa. The armies met just north of the city on 28 October. Maxentius, who had a defensible city and chose to fight in front of it, was driven back onto a bridge of boats beside the broken Milvian Bridge and drowned in the Tiber. His head was carried through Rome the next day.
The battle mattered because it gave Constantine Rome, Italy and Africa, and it is remembered because of what he is said to have seen before it.
Three accounts of one moment
Example. We have three near-contemporary treatments of the Milvian Bridge. Lactantius, writing about three years afterwards, says Constantine was warned in a dream to mark the heavenly sign of God on his soldiers' shields, and describes the mark as a letter X with its top bent over. Eusebius, writing after Constantine's death in 337 and saying the emperor swore to it personally, describes a cross of light in the sky above the sun, with words telling him to conquer by this, seen by the whole army, followed by a dream in which Christ appeared. The Arch of Constantine, dedicated in Rome in 315, says the victory was won by the prompting of the divinity and by greatness of mind, and carries no Christian symbol anywhere on it. Set them side by side.
The pattern is the clearest example of source growth in this course. The earliest account is the most modest: a private dream and a mark on shields. The latest is the most spectacular: a public daytime miracle witnessed by an army, told at second hand a quarter of a century later by a bishop writing a panegyric of a dead emperor he admired. Between them, and closest of all to the event, stands a monument voted by the Senate three years afterwards which describes the divine help in terms so carefully unspecific that a pagan senator and a Christian courtier could each read it as their own.
The right conclusion is not that Eusebius lied. It is that a story of this kind acquires detail, witnesses and precision as it is retold, and that the historian's rule is to prefer the earliest version and to treat every later improvement as improvement. Notice also what all three agree on, which is that Constantine attributed the victory to a god and said so publicly and immediately. That much is secure, and it is the part that had consequences.
Now you. Does it matter whether Constantine was sincere?
Answer
For the history, much less than the question's popularity suggests, and the evidence does not permit an answer anyway. What can be established is behaviour over thirty-one years: he legislated for the church repeatedly, built at enormous expense, exempted clergy from public burdens, gave bishops legal powers, intervened in doctrinal disputes he could have ignored, raised his sons as Christians, and was baptised as he died. He also retained the title of chief priest of the Roman state cult, kept pagans in the highest offices, and allowed a temple to his own family in Italy. Cynicism and conviction predict the same career, which is why two centuries of argument have not settled it.
What matters is the structural change, and it is independent of his motives. Before Constantine the church was an unauthorised organisation with no legal standing and no property rights. After him it had money, buildings, exemptions, courts and access to the emperor, and its internal quarrels were imperial business. That is a permanent alteration to the Roman state, and it would have been the same alteration if he had been a complete opportunist.
What was actually decreed, and when
Two corrections belong here, because the popular account of Constantine legalising Christianity is wrong in both date and instrument.
Christianity had already been legalised. In April 311, dying and in the middle of the persecution he had pressed hardest for, Galerius issued an edict permitting Christians to exist again and to rebuild their meeting places, on condition that they pray for the emperor's safety. That is the legal turning point, and it was made by a persecutor, on the grounds that the policy had not worked.
What happened in 313 was not an edict and was not issued at Milan. Constantine and Licinius met at Milan and agreed a policy; what survives is a letter Licinius sent to provincial governors afterwards, preserved in Latin by Lactantius and in Greek by Eusebius. It goes further than Galerius by granting freedom of worship to everyone and ordering the restitution of confiscated church property at state expense, which is the operative and expensive part. Calling it the Edict of Milan is a convenience that has misled generations about what kind of act it was.
The coin that lasted seven hundred years
At Trier around 310, Constantine began striking a new gold piece at 72 to the Roman pound.
Example. Work out its weight, compare it to Augustus's aureus, and explain why gold could be stabilised when silver could not.
A Roman pound of 327 grams divided by 72 gives 4.54 grams. Augustus had struck 42 to the pound, or 7.79 grams, so the new coin is 42 per cent lighter. That is not a debasement in the third-century sense, because the metal is pure and the weight is stated by the standard: everyone knows a solidus is one seventy-second of a pound, and the coin can be checked on a balance. What had destroyed the silver coinage was not lightness but the pretence that a copper-washed token was still a denarius.
Gold could be held to a standard for two reasons the previous lessons supply. The state controlled the mines and had just confiscated the accumulated treasures of temples across the empire, so it had bullion. And the gold coinage did not have to bear the mass payments: an army fed and clothed by requisition in kind does not need to be paid in millions of pieces of good money. Gold could therefore be reserved for taxes the state wanted in gold, for donatives, for salaries of officials and for large transactions, where a reliable coin is worth most. The solidus held its weight and fineness essentially unchanged for over seven hundred years, which makes it the most durable currency standard in recorded history.
Now you. Who gained from a stable gold coin, given that the everyday currency remained a copper token that continued to lose value?
Answer
The state, the army's officers, the landowners and the officials, which is to say everybody with access to gold. Taxes were increasingly demanded in gold, and certain levies fell on merchants and craftsmen specifically in gold, so those without it had to obtain it by selling into a market where their own coin was worth less every year. A soldier or an official paid in solidi had a currency that held; a small trader holding copper watched his savings evaporate.
That is a redistribution, and it is one of the more important facts about the fourth-century empire. The monetary system worked well for the top of society and badly for the bottom, and it did so structurally rather than by accident, because a two-tier currency is the natural outcome of stabilising the metal a state can control while continuing to issue tokens for everything else. It is also part of why the late empire looks simultaneously richer and harsher than the early one: the great estates of the fourth century are real, and so is the pressure on the people below them.
A new Rome
In 324 Constantine defeated Licinius and became sole ruler, and in 330 he dedicated a new capital on the site of the Greek town of Byzantium, on the strait between Europe and Asia.
The choice was strategic before it was anything else, and the previous lessons explain it. The frontiers that mattered were the lower Danube and the Persian border, and the site sits between them, on the crossing every land route uses, with a deep sheltered harbour and water on three sides. It could be supplied by sea from Egypt, and it was defensible in a way Rome was not.
It was also a Rome. It had a senate, a corn dole, hills counted to reach seven, and the emperor's residence, and Constantine stripped statues from the cities of the east to furnish it. What it did not have was the old aristocracy, the old priesthoods or the old memories, which was much of the attraction. Rome itself remained ceremonially supreme and politically peripheral, a place emperors visited, and by the end of the century some did not visit at all.
The church as a public institution
The most consequential decisions were administrative, and they show best in what they broke.
Example. In 313 Constantine exempted Christian clergy from the compulsory public duties owed by men of property, principally membership of city councils. Within a few years he was legislating to stop wealthy men entering the clergy. Read the sequence.
The exemption was meant as a favour to a small body of men, and it collided with the situation the previous lesson described: council membership had become a hereditary burden that the propertied were desperate to escape, and the state was already legislating to stop them escaping by other routes. Ordination now offered a legal exit, so people took it, and Constantine had to rule that decurions and those eligible to be decurions could not be ordained.
Two things follow. The first is that a privilege granted to a religious body immediately became a fiscal problem, which is what happens when a church acquires legal standing inside a state that assigns duties by status. The second is more general and worth carrying: legislation is evidence of behaviour, and repeated legislation is evidence of failure. The fourth-century codes return to this question again and again, which means men kept doing it. If you want to know what people were actually doing in the later empire, read what the emperors kept forbidding.
Now you. In 325 Constantine summoned bishops from across the empire to Nicaea, paid their travelling costs, attended in person and pressed them towards agreement. Why would an emperor involve himself in a dispute about the relationship between God the Father and God the Son?
Answer
Because he had made the church part of the machinery of the state, and a divided church was therefore a divided administration. He had already been dragged into the African quarrel over clergy who had handed over scriptures during the persecution, with both sides appealing to him, and he had learned that once the emperor funds, exempts and privileges a church, he necessarily has to know which body is the church.
There is also the older logic of this course. Roman religion was a bargain in which correct performance secured divine favour for the state, and an earlier lesson showed rites repeated from the beginning when they were performed wrongly. An emperor who had attributed his victory to the Christian God had every traditional reason to want that God worshipped correctly and unanimously, because incorrect worship endangered everyone. Constantine's letters say almost exactly this: he treats the dispute as a disaster threatening the peace he had been given, and he is visibly baffled that anyone would risk it over a question he calls small and unnecessary. He was wrong about it being small, as the next lesson shows, but the instinct behind the intervention was thoroughly Roman.
What he did not change
It is worth ending with the continuities, because the temptation is to treat 312 as the hinge of everything.
The state Constantine ran was Diocletian's, essentially unaltered: the provinces and dioceses, the prefectures, the separation of civil from military command, the tax in kind, the enlarged army, the court ceremonial and the remote sacred emperor. He kept the persecutor's machinery and pointed it in a different direction, which is one reason the change was possible at all.
Nor did he make the empire Christian in any straightforward sense. Traditional cults continued and were funded; the Senate at Rome remained largely pagan for two more generations; and the growth curve of the previous lesson, running at around a tenth of the population in 300, does not reach a majority by his death in 337 on any reasonable assumption. What he did was make Christianity the religion of the state's rewards, which changed the incentives of everybody with a career.
He also left the question of doctrine unsettled. Nicaea produced a formula, and it did not produce agreement, and the empire spent the next fifty years arguing about a single word with emperors on both sides. That argument, and what it did to the relationship between bishops and the state, is the subject of the next lesson.