A History Of Christianity (2009) s01e02 Episode Script

Catholicism: The Unpredictable Rise of Rome

Eighty years ago, my mother was a little girl in the Staffordshire Potteries.
One day she was out walking with my grandfather, devout pillar of his local Anglican parish church, when they passed a church that she thought she'd like to look into because it was Roman Catholic and she had a girl's curiosity about it.
Her father made it quite clear that he would be highly displeased if she even went inside a Roman Catholic church to look round.
For him, Rome was an alien world, liable to pollute the English way of life.
That seems a world away now.
And my grandfather isn't around to stop me exploring.
So my second journey into Christianity takes me into the history of the church which calls itself Catholic.
Its headquarters is the Vatican in Rome, an independent sovereign state with influence all over the world.
Over one billion Christians look to Rome.
That's more than half of all Christians on the planet.
But there's a huge paradox here.
How did a small Jewish sect from first century Palestine, which preached humility and the virtue of poverty, become the established religion of Western Europe, powerful, wealthy, and expecting unfailing obedience from the faithful? It's a story of what can be achieved when you have friends in high places.
(CROWD CHEERING) DIARMAID: The centre of the Western Latin Church is the city of Rome.
And the spiritual head of that church is the Bishop of Rome, the Pope.
And that's very odd when you think about it because Rome is the centre of the empire which killed Christ.
And the empire went on killing members of the church for another 300 years on and off.
(CHANTING) So what happened to give Rome a Christian destiny? DIARMAID: The obvious focus for the newly emerging church was Jerusalem.
It's where Jesus was crucified.
But in 70 A.
D.
The Romans destroyed the city.
Christianity gradually spread south and east.
But one missionary, the Apostle Paul, looked in a different direction, to Asia Minor, now modern Turkey, and Greece.
His letters in the New Testament trace his journey through the trading routes of the empire whose capital was Rome.
And eventually, as a prisoner of the emperor, Paul came to Rome.
It's said that he was met by his friends here on the Appian Way, just outside the city, that he then spent years under house arrest before the Roman authorities killed him.
DIARMAID: With the perversity of history, Rome's brutality would put the city centre stage for Christianity.
Like Jerusalem, Rome could now claim a piece of the Christian story.
From very early on, Christians were drawn here to the underground catacombs of San Sebastiano where Paul's body was hidden from the authorities.
But they were also drawn to another martyr's grave.
Simon Peter, one o f the 12 original disciples of Jesus.
Peter and Paul are equally venerated in these graffiti from the third century.
At that stage, there was no hint that one of them would become the sole spiritual leader of the church, nor that the Roman Empire would become Christian, or Rome the centre o f a worldwide Christian church.
So what on Earth, or what in Heaven, happened? This is the first glimpse that many early Christians had of Rome.
It's the port of Ostia, about 12 miles southwest of the city.
The first Christians in the west were Greek speakers, travelling merchants or slaves who sailed here from trading ports all round the Mediterranean.
These Christians met together in secret to share an idea which has seized millions across 2,000 years.
Eternal salvation is open to anyone who believes in Jesus Christ as the Son of God.
And at the heart of their new faith was a ritual symbolising selfless love, sharing a meal.
The Christian people went on breaking bread and drinking wine in thanksgiving for Jesus Christ, and they probably did so here, in this family home, and the clue to that is in the mosaic.
It's got fish in it and fish are a secret Christian symbol because the first letters in Greek for fish are the same as the first letters in Greek for Jesus Christ.
DIARMAID: Christianity began creeping in from the fringes of Roman society.
Church buildings started openly appearing.
This is just one of at least two in the port of Ostia.
By the year 251 the church in Rome had on its books 46 priests, seven deacons and 52 exorcists, readers and doorkeepers.
If you were a traditional-minded Roman, you'd notice all this.
You'd notice crosses appearing on floors and walls, and you wouldn't like it.
The gods would be offended.
Stories spread that Christians actually drank blood during their ceremonies.
Well, after all, that's what they said they did.
But the rumours grew.
Christian love feasts were said to be incestuous orgies.
And although Christians were a non-violent sect, their refusal to sacrifice to the emperor looked like treason.
Christians became scapegoats for a whole heap of new threats to the Roman Empire.
Economic crisis, social breakdown, civil war.
It culminated in a savage attack on Christians, right across the empire.
In the Great Persecution at the end of the third century church buildings were destroyed, and all Christians were required to sacrifice to the pagan gods.
Some of those who refused are said to have been slaughtered here in the theatre at Ostia.
It had never been this bad.
The Roman Empire was now gleefully killing Christians, just as it had killed Christ two and a half centuries before.
You'd have been mad to think that Rome could be the centre of worldwide Christianity.
But Christian fortunes were about to change dramatically.
One emperor did a reverse turn which took Christianity from a religion of the poor and dispossessed into a religion of the rich and powerful In the early fourth century, the Roman Empire was torn apart by rival claims to the imperial throne.
During the struggle for power, one general and ruthless politician made a decision which changed the course of Christian history.
Because of that, Christians have called him Constantine the Great He made the decision to become a Christian.
For reasons which lie buried forever in his mind, he became convinced that the Christian God had helped him hack his way to power.
This was the God whose followers were still being persecuted by his rivals and that might have had something to do with it.
DIARMAID: When Constantine had secured supreme power in all Roman territories in the east and west he set about making the empire Christian.
To secure the eastern half, he moved his capital to a small Greek city overlooking the Bosphorus which he named after himself, Constantinople.
But he had plans for Rome, too.
Rooting out Rome's pagan past and remodelling Christianity into a state religion.
Constantine was a generous benefactor of this church, St Martin on the Mount.
It's rather off the tourist map.
But in here there's something very special, a glimpse of the true scale of Constantine's vision for a Christian Rome, a new Jerusalem with churches to outshine the ancient imperial buildings of the Roman past.
And here it is.
A church which became one of the most famous in Christian history, the Basilica of St Peter.
And it's one of the few decent views of what old St Peter's looked like inside.
In a word, huge.
Today St Peter's Basilica is the centrepiece of the whole Catholic Church.
And if there's one thing that the modern papacy really pushes at the faithful, it's that Rome knows best.
The centre is what matters.
The crucial steps towards centralised power were taken 30 years after Constantine's death, during the time of Pope Damasus I, when the bishop of Rome was established as bishop in unbroken succession from St Peter.
Well, I'll stick my neck out and say that I don't believe that Peter was bishop of Rome.
And you'd be hard put to find anyone before the time of Pope Damasus who made that claim.
But as successor of Peter, the bishop of Rome became the holy father, pope of all Christians in the west.
Now Damasus set out to give Christianity the glory which an imperial religion demanded.
He brought the good news, not to the poor and the downtrodden to whom Jesus had preached, but to the Roman nobility.
There's a monumental room just above the catacombs of San Sebastiano which shows precisely how.
Well, this chamber may not be much to look at now but it's something very precious because it's a building actually commissioned by Bishop Damasus himself, and what it is, is a luxury mausoleum for the aristocratic members of his congregation in Rome.
DIARMAID: Pope Damasus also personally composed Latin inscriptions glorifying the suffering of the Christian martyrs.
There's rather more elegance than evidence in what he wrote.
This is actually one of Damasus' inscriptions.
It's about a very obscure saint called Eutychius.
(READING IN LATIN) "Eutychius the Martyr showed that he could conquer the evil commands "of the tyrant and the ways of the world.
" But what's nice about it as well is the lettering.
It's the best, most expensive imperial lettering you could get, like on an imperial Roman inscription.
It's a symbol that the church is no longer the church of a few Greek-speaking traders.
It's the church of all Roman society at all levels.
To round off his claim that the Western church was the legitimate heir to the original church of Jerusalem, Damasus commissioned a new translation of the Bible in fine classical Latin.
The man he chose for the job was his secretary, a scholar called Jerome.
Jerome's work was so thorough and impressive that it's been the approved Latin translation of the Bible ever since.
It was called the Vulgate from the Latin for "generally known" or "common", and that's a very significant word.
While the eastern half of the emperor's church went on speaking Greek the western church was now committed not just to worship, but to think in Latin.
DIARMAID: The Catholic Church was no longer an upstart.
It had friends in high places.
Now a religion fit for gentlemen.
But I don't want to leave the impression that the Catholic story is just about power politics.
If you're in any sense a Western Christian, you live with one legacy in particular from this period, even if you fight against it, the idea that Adam and Eve have left us totally corrupted by sin.
That was the conclusion of Augustine, Bishop of Hippo in North Africa, the father of Western theology.
As a young man Augustine lived the life of a playboy.
He was also a scholar with a brilliant career ahead of him.
But it all turned sour.
Then in a garden in Milan came a moment when he began to see a purpose in his life.
He heard a child chanting, "Toglie e legge.
" "Take up and read.
" Augustine opened Paul's Epistle to the Romans at random.
Paul confronted him with his own sin and told him that the only way to salvation was through purity of life.
Augustine became obsessed with the source of sin in Adam and Eve's disobedience to God and his answer bequeathed the Western Latin Church an idea which not every Christian has found in the Bible, original sin.
Augustine came to believe that all humans inherit sin from the sin of Adam and Eve, and that sexual desire is an appetite of the baser physical body, rather than the soul, and that the sexual act is the way that sin is transmitted from one generation to the next.
It means that you and I are so corrupted by sin there's nothing we can do to save ourselves from Hell.
Only God can do that by his grace.
And there is no reason why he shouldn't make completely random decisions as to who to send to Heaven and who to leave in Hell.
We have no say in the matter because we're nothing but corruption.
That idea of predestination still hangs around Western Christianity, Catholic and Protestant, as does Augustine's dark view of sex.
And maybe the modern West is so obsessed with good sex as the symbol of a fulfilled life, precisely because the Western Latin Church has been so long obsessed with bad sex as the root of human sin.
The Christian church's humble beginnings were now a distant memory.
A golden age seemed to beckon.
But this turned out to be a mirage.
In the fifth century barbarian invaders overran the western half of the empire.
And in 410 they took Rome itself.
At that moment, the Latin Church could easily have crumbled and become a footnote in European history.
To see what happened I've come to north Italy and the city of Ravenna.
The centuries while the church stood alone after the fall of Rome are often called the Dark Ages, as if civilised life collapsed.
Actually that's not true.
The church was not about to die with the empire, but it was at a crossroads.
DIARMAID: A choice of routes lay ahead.
This is the Church of San Vitale.
It marks one possible future, to look east to Byzantium, the surviving half of the Roman Empire and one half of the imperial church.
San Vitale was built by an emperor of the East, Justinian, whose ambition was to win back the whole territory of the old Roman Empire.
Ravenna was one of his conquests, the Church of San Vitale one of his legacies.
Eventually his branch of imperial Christianity would become Orthodoxy, and flourish in the Balkans and Russia.
But there was another option for the Western Church, even more radical It could choose to do some sort of deal with the new barbarian rulers.
With the invading Franks in Gaul, Visigoths in Spain, Vandals in the African provinces, Ostrogoths in north Italy.
Contrary to the image of barbarians, these people were not savages.
Most of them were already Christians, j ust not Catholic Christians.
I've come to the Church o f Sant' Apollinare Nuovo, also in Ravenna.
It was built for Theodoric, King of the Ostrogoths.
The trouble was, in the eyes of the Catholic Church, everything about his Christianity was heretical.
He was a follower of Arius, who believed that Jesus Christ was not fully eternal and divine in the way that God the Father was.
Now what's so precious about this place is that it's not just an Arian Church building.
We've got Arian pictures, mosaics.
We've got the life of Christ, miracles, we've got the miraculous draught of fishes, for instance.
But on this wall, what's so great is that he's a young Christ.
He's got no beard.
When we go round to this side, later scenes in the life of Christ, like his betrayal in the Garden of Gethsemane, he's got a beard! So, the Arian Christ, like us, he grows older.
He's human.
Faced with the choice of an alliance with the east or with the Arians, what would the Latin Church do? Its decision forever shaped Western Christendom.
It decided to go it alone and look to the Pope to guide it And in the end, it was the Latin Church which survived intact, and it was Arian Christianity which was wiped from the record.
Well, we've got an intriguing case of Catholics censoring mosaics here.
Because this is a picture of a palace, it's helpfully labelled "palatium".
And it's the palace of the Arian King Theodoric.
But he's missing! He would be where that great area of gold mosaic is, but he's gone.
And either side of him would be his courtiers.
But instead of the courtiers, you've got these rather boring curtains.
But they haven't done it very well, because, you see, they've left hands on the columns.
Hand, hand, fingers! There, they've gone.
They just don't exist any more.
So how did the Latin Church survive on its own? Well, the decisions made by that wily politician Pope Damasus began to pay off.
The church still had influential friends.
The Latin Church survived because of a great choice made by people clinging to shreds of imperial power, the Roman aristocracy.
Once they'd ruled the empire.
Now they decided to rule the church.
Roman noblemen became bishops to preserve the world they loved.
And when the empire collapsed, the church stepped into the power vacuum.
DIARMAID: The Western Church had survived.
It had adapted.
Four hundred years earlier Christianity was against the establishment Now, it was the establishment Not surprisingly, the bishops of Rome were in an expansive mood.
Rome would play a new role, as the capital of a Western Christian empire of the mind, greater than any empire created by the Roman army.
The church no longer had the backing of imperial might, but it had one institution which was a Christian powerhouse for just such a mission.
The monastery.
I'm in central France, just outside Poitiers, and this is Ligugé Avbey, probably the very first monastery in Western Christianity.
It was founded in 360 A.
D.
By one of the earliest monks in the West, St Martin of Tours.
(CHANTING) DIARMAID: Many miracle stories quickly grew up around Martin, and even at the time, one or two people who'd known him found some of them rather hard to take.
This chapel here commemorates one of the best known ones of them, which is that he actually raised a young man from the dead.
DIARMAID: Now whatever the truth of these stories, what really mattered about Martin was that he had power.
(BELLS TOLLING) St Martin exploited his charisma to the full, using an approach to Catholic expansion that would be the model for Catholic conversion for the next 800 years.
First convert kings and queens, the rest will follow.
(ALL CHANTING) Monks prayed for the salvation of royalty and noblemen, but they also gave all society something which it desperately needed, a sense of order, design, harmony.
Monasteries became beacons of order, thanks to a rule attributed to a monk called Benedict.
And the community of Ligugé Avbey live under that rule today.
- Homemade.
- Well, yes - Oh, no, take two.
- Monastery made.
Oh, well, no, one will be enough.
One will be enough.
Oh, it's so light.
It's delicious.
Of the monastic vows of poverty, chastity and obedience, I think obedience is the most difficult for modern individualists to understand, especially that bit of the Benedictine rule which allows the abbot to beat his monks.
But the aim was to strike a balance between the spiritual development of the individual monk and the peace and well-being of the community, and you have to remember that this was a terrifyingly lawless age and people longed for the lost security of the Roman Empire.
DIARMAID: Hundreds of Benedictine monasteries were founded.
They were a vision of God's imperial court in heaven.
Between the fifth and the ninth centuries the midwife of Catholicism in Europe was not imperial might, it was the monastery.
Now the Arian people had brought their own Christianity westwards, too, as far as Spain.
But Rome would outflank them.
The pope sent a mission reaching beyond the Arians, to the former Roman colony of Britannia.
In 597 a party of 40 Roman monks and priests landed in Kent They had been sent by Pope Gregory I, himself a monk and one o f those Roman aristocrats who had taken over the church.
It's said that his mother, Silvia, sent his monastery daily meals on a silver dish.
Gregory couldn't have been less like an upper-class twit playing at being a monk.
He was the first pope to take an initiative in mission to the boundaries of the lost empire.
It was led by a monk from his own monastery in Rome, a priest called Augustine.
Augustine's often been celebrated as the man who brought Christianity to England.
Actually, it wasn't quite like that.
Britannia already had some Christians from its days as a Roman province.
In fact, Augustine and his 40 monks were offered a church in Canterbury.
This church.
They were welcomed here because the King of Kent's wife was a Christian.
And there she is in the stained glass, Queen Bertha.
This church building dates right back to the Roman occupation.
It's probably the most continuously used parish church in England, dedicated to Martin, St Martin of Tours.
DIARMAID: But the reality was that for two centuries, Britannia had been ruled by non-Christians, Anglo-Sax on warriors from mainland Europe.
Augustine's mission was to win back Britannia, convert the Anglo-Sax ons and make Canterbury his Rome.
For that he needed a much bigger centre of operations to match his ambition.
This is all that remains of St Augustine's abbey.
Look, I know this doesn't look very exciting to the uninitiated, but this is really special.
This is a reused Roman pillar in a seventh century church which Augustine may have seen and certainly someone who knew Augustine saw.
This is quite unique.
DIARMAID: In the mere eight years of life left to him, Augustine laid a solid foundation for an Anglo-Sax on Church which was quite exceptional in Europe in its devotion to Rome.
His seat of power, Canterbury Cathedral, was given the dedication Christ Church because it was then the dedication of the pope's cathedral in Rome.
It was the pope who appointed Augustine the first archbishop of Canterbury.
And in fact, Pope Gregory gave Augustine a special liturgical garment, the pallium, and this was a symbol that the power of the archbishops of Canterbury came from Rome.
It's easy to forget that the English Church was under Roman obedience for 900 years, far longer than it's been Protestant Eventually, the Church of England turned its back on the Church of Rome in the 16th century Reformation.
But it forgot one little thing.
Bizarrely, the coat of arms o f the archbishop of Canterbury still incorporates the Y-shape of the pallium.
It's a little piece of heraldry which the Protestant Reformation in England either failed to notice or decided to ignore.
When Augustine died, there were around a dozen monasteries in England.
A century later, there were at least 200.
(ALL CHANTING) But these distant isles made their own special contribution.
They gave shape to one of the distinctive practices of the Catholic Church, confession.
I've come as far west in Europe as you can get to where monks lived a life as intense and austere as anything in church history.
I'm heading for Skellig Michael, off the Kerry coast in Ireland.
These monks were not Anglo-Saxon, but Celtic Christians.
They came to settle out here in the Atlantic Ocean, as far back as the sixth century.
It's easy to see them as isolated from the church in Rome.
But for them, the sea was not a barrier, but a series of pathways to their neighbours and beyond.
They shared books with other monks right across the Mediterranean, and Latin was the language of their liturgy and their literature.
These are man-made steps, 600 of them designed by the monks to take me up to the monastery.
Well, I have to confess that I started up these stairs cheerfully enough but vertigo has taken over and I simply can't go on.
So I will never see the monastery on Skellig Michael.
I cannot understand why the monks lived here.
It feels like the edge of the world.
DIARMAID: It seems absurd to me that, living here, Irish monks could have an upbeat view of human nature.
But they did.
Such a contrast with the pessimism of Augustine of Hippo.
And out of this optimism came a new practice designed to cope with that sense of guilt and falling short that Christians call sin.
They came up with tariff books, guide books to dealing with sin.
The principle is you can find out or decide what sort of penalty, penance deals with what sort of sin, and you can list them, and there they are for priests to deal with.
Who wouldn't jump at the chance of having a forgiveness-of-sin tariff? And this is the beginning of individual confession to a priest.
It's a very powerful thing to do, to offer someone forgiveness.
Confessions remain very precious for Catholics, but it's also been an enormous source of conflict and anger in the Western Church.
That's because forgiveness is very personal.
So is a priest getting in the way or is he helping you reach out to God? That idea doesn't sit very well with Augustine of Hippo's views about total human corruption.
And aren't you rather manipulating God by setting up measurements for forgiveness? The clash between those two thoughts went on lurking in the life of Latin Christians.
In the 16th century Reformation it was the central issue to split the Western Church.
It's an impressive witness to the energy of Ce ltic Christians that this remote corner of Europe had such a profound influence on the whole church.
Western Latin Catholicism had not faded during the so-called Dark Ages.
It had survived, and more than that, it had spread its Christian message to a world beyond Rome.
But it was still vulnerable.
With the emperor gone, it was at the mercy of kings and noblemen who were often little better than bandits.
And a new religious rival had risen in the East.
Islam.
At the end of the eighth century, with Islam relentlessly pressing westward, Pope Leo III turned the clock back 400 years and made Western Christianity an imperial power once more.
Just like Constantine I, the new emperor, Charles, would be nicknamed "the Great", Charlemagne.
The ancient spa town of Aachen in southwest Germany was once home to Charlemagne, the most powerful man in eighth century Western Europe, but also, a man with a fetish for history.
Charlemagne loved to wallow in the hot pools of Aachen, pretending to be a Roman at the baths.
But he was actually descended from barbarians, the Franks.
They were one of the peoples who'd swept into Western Europe and smashed the central structures of the Roman Empire.
But the Franks were different from the other barbarians.
They'd taken up Catholic, rather than Arian, Christianity.
DIARMAID: Charlemagne's empire extended from beyond the Pyrenees into the heart of modern Germany.
But his ambition was to reunite the old Roman Empire, west and east, a Christian Roman Empire.
His first priority was to become the protector and defender of the Catholic Church.
In return, Pope Leo III crowned him as emperor of the west on Christmas Day, 800, in St Peter's Basilica in Rome.
Charlemagne's successors called themselves Holy Roman emperors.
And many of them were crowned on this throne, in Charlemagne's cathedral in Aachen.
No pope before had crowned monarchs.
Did this now mean that the church was mightier than the empire? For the next few centuries, popes and emperors quarreled about who best represented Christian Rome and which side had supreme authority over the other.
There never was a clear answer.
But at least emperor and pope shared a vision, an imperial Western Latin Church.
And that gave Latin Christianity a new self-assurance.
Two hundred years later, in 1054, the West would finally split from the church in Constantinople creating distinct Catholic and Orthodox churches.
Far from damaging the Western Latin Church, the split became the platform for an ambitious new pope, Gregory VII, to revolutionise the church.
So much has happened to the Roman Catholic Church in the centuries since then, but it's still indebted to Gregory's reforms a thousand years ago.
The big theme of Catholicism has come to be the centre.
Central control is now what matters, and what marks it out from other denominations.
What Gregory now wanted to do was to micro-manage the fate of every soul in Europe.
And to drive through this change, the papacy first targeted the clergy.
Gregory made a change which was to redefine the popular image of the Catholic cleric.
Before that, most clergy who were not monks would expect to marry.
But Gregory started a campaign to make all clergy automatically celibate.
That's because he wanted the best, the most disciplined and the most loyal clergy possible.
With its foot soldiers in place, the church now had a presence in every village and town, every parish, doing its best to control every aspect of people's lives.
What emerged was a single Western Latin Catholic society unified by the Latin language and underpinned by a complex religious bureaucracy.
It reflected the lost Roman Empire, it outshone the Roman Empire.
And what was it all for? Nothing less than making all society holy.
(MAN CHANTING) But far and away the most centralising step was taken by the pope himself when he told the world what he thought he was or what he'd like to be, a universal monarch reigning over all the rulers of the Earth.
But this was not just a greedy church grabbing power.
It was also intended to offer something to the faithful.
Not just any old something, salvation.
For a thousand years, the Christian picture of the afterlife had been stark.
After death, you either went to Heaven or Hell But now the Latin Church picked up an old idea from early centuries.
Purgatory, a place for purging, where the souls of the dead burned in fire.
The difference from Hell was that Purgatory wasn't forever.
And Purgatory had only one exit, up to Heaven.
It was tailor-made for those who in this life feel ordinary, not very good, not very bad, but certainly not good enough to go straight to Heaven.
It was a very comforting doctrine.
Crucially, it gave people a sense that while still on this Earth they could do something about their salvation.
They could pray or they could do good works to shorten their time in Purgatory.
The whole system became an industry in the Western Church, the Purgatory industry, a vast factory of prayer and ceremonial observance.
It was one of the most successful ideas in the whole of Christian history.
It satisfied millions of people for centuries on end.
By the end of the 11th century, the Catholic Church was European society's single most important institution, the best-organised monarchy in Europe.
It promised a structure to people's life on Earth and salvation in death.
That's more than the old Roman emperors could ever have offered.
But the reality was that half o f the world's professing Christians were now subject to a different religion.
Islam controlled the whole of North Africa, Spain, Sicily and much of western Asia.
It even occupied the original holy city, Jerusalem.
And so, in 1095, in a great blaze of publicity, the Catholic Church mounted an ambitious military campaign, the First Crusade.
There'd been a time when Christian leaders had tried to stop Christians from becoming soldiers.
Now atrocities were committed in the name of the God of love.
For the first time, the notion of holy war entered Christianity.
The Crusades are an embarrassment for Christianity.
In seeking to recapture the Holy Land, they caused misery and destruction.
It was idealism, but it was also Christian love turned to violence and arrogance.
But I'm here in London, at the Temple Church, to show that the Crusades left a more complex legacy.
Some say this is modelled on the Church of the Holy Sepulchre in Jerusalem.
But I think that's to hide an awkward truth.
It's a copy of one of the most famous Muslim buildings in the world.
It was built by the Knights Templar, an order of soldier monks founded during the Crusades, to protect pilgrims to the Holy Land.
They'd seized the Temple Mount in Jerusalem and made it their headquarters, hence the name Templars.
All over Europe, they built these circular churches to look like what they thought was the Jerusalem temple.
It's a good thing they didn't realise that it was actually a Muslim building, the Dome of the Rock on the Temple Mount.
DIARMAID: This was the Templars' English HQ.
Burial here in the round church was almost as good as being buried in Jerusalem.
These knights are portrayed in their early 30s, the age at which Christ died and the age at which the dead will rise on his return.
Men like these flocked to join the enterprise.
The Crusades became yet another means of purging sin, like purgatory, but this time through action in this life.
And that led to a further new Western Catholic idea.
The Crusades were sold to noblemen and humble folk alike as another way of winning salvation.
Whatever sins someone committed on crusade were more than cancelled out, simply by being on crusade.
And this was the first specimen of something which became big business in Western Europe alongside Purgatory, the indulgence.
An indulgence granted you time off from Purgatory.
Later, they became as routine as the modern lottery ticket for a good cause.
In the end, you simply bought them.
Even now the idea of crusade has its defenders.
But I have to say that I find the crusading era one of the darkest chapters in the history of Catholicism.
There was at least one positive and hugely important outcome of the Crusades, a legacy that's still with us now.
I wouldn't be a professor without it, so it must be good.
Thanks to the Crusades, Islam gave us universities.
And my employer, Oxford University, was one of the first.
Academic robes, professorial chairs, lectures, the qualification of a degree itself are not Western ideas.
They are all copied in remarkable detail from medieval Islamic schools of higher education, and all to cope with the flow of new information pouring in from the Middle East.
DIARMAID: And it was only really the death of Edward VI which stopped Melanchthon coming.
He seems quietly to have pocketed the travel expenses and not sent them back, but he was very wise because (SPEAKING LATIN) DIARMAID: In many ways, the Crusades mark a watershed in the history of the Latin Church.
In a thousand years, the small persecuted Jewish sect had risen to a peak of unprecedented and, frankly, unexpected power.
Certainly no one could have expected the Roman papacy.
But what was much more predictable was rebellion against the concept of papal monarchy.
Dissent would now cast a long shadow over the church.
It led to more innovations, some of which are difficult for modern Christians to comprehend, or even to forgive.
At a great council of the church in 1215, Pope Innocent III tried to secure the loyalty of the faithful by spelling out what it meant to be a Catholic.
Confession and communion at least once a year.
The council also told people what to believe about the mass.
Bread and wine miraculously become the body and blood of Christ.
And they helpfully recommended a way in which philosophers could explain this miracle, transubstantiation.
That's a big word for ideas taken not from the Bible, but from Aristotle, who lived long before Jesus Christ.
Failure to accept that the mass was a miracle could land you into trouble.
And there were plenty of other forms of religious energy which unnerved the pope, like the Cathars who rejected the mass altogether.
Of course, churchmen didn't mind religious fervour in itself.
It was when it got out of their control that they got worried.
And then they were quick to label it heresy and punish it.
DIARMAID: Pope Innocent III created structures to deal with heresy, inquisitions.
The English didn't actually use them, but this medieval courtroom in the University Church of St Mary in Oxford gives you a sense o f what it must have felt like to be in front of the inquisition.
It's still the official courtroom o f the Anglican diocese of Oxford.
It's difficult for modern Westerners to understand the mind of an inquisitor.
But we need to remember that they were clergy, and they saw what they were doing as an aspect of the pastoral role of a priest to make society better.
But there is a fine line in any system between idealism and sadism.
Inquisitions were no worse than most medieval courts.
Torture might be used to extract confessions.
Those on trial had no right to defence counsel.
Penalties ranged from wearing a cross of penitence to pilgrimage, to imprisonment, to death by burning at the stake.
That's one way of dealing with heresy, smash heretics and punish them.
The other way is to reinvent the church.
DIARMAID: To rediscover core ideas, like poverty, humility, compassion, the sort of things which Jesus Christ preached.
During the 12th century, new religious movements and maverick holy men attacked the wealth and power of the church.
Instead of handing all of them over to the inquisitions, Pope Innocent took a huge risk.
He brought them into the fold.
His hope was to regain something which the Western Church had forgotten.
The most famous of these holy men was called Francis.
It's difficult not to have heard of Francis, and it's easy to be sentimental about him, the loveable saint immortalised in stories retold to generations of children.
He talked to the animals.
Actually, you might think he was mad.
He chucked away his wealth, he proclaimed the Christian message to birds in a graveyard and he threw the church into turmoil by saying that Christ was a down-and-out with no possessions.
He might have been burnt as a heretic, as many others were.
But luckily for him, alongside his almost pathological non-conformity, Francis was deeply loyal to the church.
It was in a church, this church, where Francis heard his first call to action.
He wanted people to see the ordinariness, the humanity of Christ, so that they could love and worship him better as God.
And that made the Catholic Church more human and approachable, too.
It was Francis who invented the idea of a Christmas crib in church.
The first time, he brought along a real ox and a real ass.
He wanted to remind us of the humble origins of the Christian faith, God becoming human not in a palace, but in a stable.
This was a new, more personal, emotional view of Christ, with a mother, Mary, who suffered like any mother when her son died horribly and before his time.
So the Catholic Church accepted Francis.
It welcomed the new movements of friars who lived his message.
But it actually did nothing to shed its own wealth and power.
It's just as well Francis never saw this grand and expensive church built over the humble chapel where his mission had begun.
By the end of the 13th century, the Western Latin Church had created nearly all the structures which shaped it up to the Reformation era.
Monks, nuns and friars sent up their prayers to heaven in an ever-spreading array of religious houses.
Thousands of parish churches made up a giant honeycomb of dioceses and archdioceses across Europe.
And millions of Catholics owed their unfailing allegiance to the pope in Rome.
There would be setbacks for sure, but by the 15th century, the papacy emerged largely unscathed, powerful, wealthy and confident So much so, it invested its energies in rebuilding Constantine's St Peter's to make it the grandest building in Christendom.
But in the 120 years it took for a succession of popes and architects to complete, the world had changed.
By the time the new basilica was dedicated in 1626, Christianity had been convulsed by a new movement of revolt which had almost swept the papacy away.
In every age of Christian history, even when the church has been vigorous and self-confident, there have been restless individuals liable to claim that it could do better.
It was that sort of questioning and re-examination of Christian origins which led to the 16th century Reformation.
DIARMAID: The Reformation has proved the greatest fault-line yet in Western Latin Christianity.
But first, we need to visit that earlier and greater fault-line, when the Latin and Greek halves of the Roman Empire went their separate ways.