Here in the Church of the Holy Wisdom in Constantinople, on 16 July 1054,
a disaster unfolded for Christianity.
It was actually during a service that a papal delegation swept up to the altar and placed on it
a document excommunicating the leader of the Church in Constantinople, the Patriarch.
The Patriarch excommunicated the Pope in return.
The moment has come to be remembered as the Great Schism, a split between
Eastern Orthodox Christianity and Western Catholic Christianity.
At the time, it seemed like one petty incident in a whole series of disagreements.
But the fact remains that a thousand years later that split between East and West is still there.
Today, Eastern Orthodox Christianity flourishes in the Balkans and Russia.
And it has over 150 million worshippers worldwide.
But much of my third programme charts its fight for survival.
After its glory days in the Eastern Roman Empire, it stood right in the path of Muslim expansion,
suffered betrayal by crusading Catholics,
was seized by the Russian Tsars to ally with tyranny
and faced near-extinction under Soviet Communism.
So what is Orthodoxy?
And what is the secret of its endurance?
I'm the guest here of the congregation of the Greek Orthodox Cathedral in London.
CHORAL SINGING
What you get in any Orthodox act of worship is a fragment of a vast
annual ballet of worship, carefully choreographed
and woven into a texture of ancient music
to reflect the timelessness of God's imperial court in Heaven.
On that spoon, bread and wine mingle to symbolise
the indivisible nature of Christ who is both human and divine.
HE SPEAKS BYZANTINE GREEK
All around us are the symbols of 1500 years of Orthodox tradition.
The deeply venerated icons.
And this fierce-looking bird, the double-headed eagle.
What story is this ancient, passionate drama trying to tell us?
It pulls us back to one of the great crises of Mediterranean civilisation.
The greatest empire which the West had ever known seemed to be tottering into ruin.
From the beginning of the 4th century, the Roman Empire was Christian.
But then the Christian God seemed to give up on it.
In the West, barbarians overran it.
In 410, they seized Rome itself.
Yet still, in the Eastern half of the Empire, there was another capital beyond the invaders' reach.
Today we call it Istanbul, but that's just a version of its original name, Constantinople,
given it by its founder, Constantine the Great.
Constantine had founded his city on the site of an old Greek fishing port called Byzantion.
His dream was for Constantinople to become the perfect Christian capital.
Indeed, he thought of it as the new Rome.
Two centuries later, the dream lived on for a husband and wife
who took power in the Eastern Empire in 518.
Emperor Justinian and Empress Theodora.
They were one of the most unlikely couples
ever to rule in Constantinople.
He was a peasant from the Balkans.
She was a former circus artist of allegedly daunting sexual prowess.
Together, they set out to regain the lost territories of the Christian Roman Empire.
Instead, they created something new,
the Byzantine Empire.
Justinian moulded his new Christian Byzantine Empire round one church.
Put up in just under six years, it was far and away the largest
religious building in the Christian world.
The Holy Wisdom, Hagia Sophia.
When Justinian entered the building for the first time he was heard to murmur,
"Solomon, I have surpassed thee."
That's the sort of ambition we're seeing here.
An emperor who can outdo the Bible's most glorious king of Israel.
For nearly 1000 years, this was the scene of a constant round of sacred imperial ceremony.
The Emperor and Patriarch were the leading actors in the drama,
a union of church and throne.
Today, Hagia Sophia is clogged with scaffolding.
And frankly, there's a sadness about the place.
It takes you a while to get over that and see one of the most sumptuous spaces ever created by human beings.
The dome covers a vast congregational space,
trying to bring Heaven into daily worship.
Because the dome IS Heaven, the sky above turned into human architecture.
And that's the key difference between Eastern Christianity and the Christianity of the Latin West.
The Western Church has insisted that original sin
opened a great gulf between God and humanity.
But Eastern Christianity tells its followers
that God and human beings can meet, even unite.
It's a risky, exhilarating thought.
And nothing expresses that mystical urge to make the invisible visible more than Byzantine Art.
Even though it's an art which is the result of a theological compromise.
The solution to a big headache which all Christians face -
how to make a picture out of the divine.
The archaeological museum in Istanbul is full of sculpture from the Greek world before Christ.
Greeks took it for granted that you represent gods and goddesses with as much beauty as you can.
Christianity took shape in this Greek world.
But Christians also believe that Jesus was the Jewish Messiah.
That points to a great fault line running through all Christianity.
Greeks thought it natural to portray the divine as human but Jews came to find it profoundly shocking.
Jews stuck to their second commandment -
"You shall make no graven image for yourself, you shall not bow down to them or serve them."
Who were Christians to follow, Jews or Greeks?
The Western church tied itself in knots on this question.
But Eastern Christians did something rather ingenious.
They simply created art that was not graven.
In other words, nothing sculpted, just flat surfaces.
The busy jewelled walls of mosaics, or paintings on wood.
And those wooden painted tablets became the defining feature of the Orthodox Church, the icon.
This is not just art,
it's a three-way meeting, between artist, worshipper and God.
Very few of the first icons survive.
To see them, I've had to travel to the fringes of the old Byzantine Empire.
The Sinai Peninsula, in modern Egypt.
Here at the foot of Mount Sinai
is one of the most ancient Christian monasteries in the world.
Back in the 6th century, it was a frontier-post for the Byzantine Empire
and another proof of the Emperor Justinian's enthusiasm for Christian building.
Within its great fortress walls is the world's oldest collection of icons.
The word icon means just what it says.
The Greek word for "image".
A face, a person, a scene
painted on a portable wooden panel in special, prescribed ways.
God, Christ, the saints of the Church.
Icons invite the worshipper to stand not before a painting, but a real person.
Each of them is an invitation to climb a ladder to Heaven.
CHANTING
Icons are focal points in every Orthodox church.
They cover a screen in front of the altar called the iconostasis.
Today, you couldn't imagine Orthodox tradition, so mystical, so ancient, without icons.
But it wasn't always so.
From the 7th century a series of emperors did their best to wipe out icons from Byzantine religion.
And strange though it may sound, it was because they'd begun to doubt that God was on their side.
There was a good reason to worry, a sudden and unexpected
challenge to the Byzantine Empire from a new religious force, Islam.
By the middle of the 7th century, Muslim armies had snatched two thirds of Byzantian territory,
including the great holy cities of Damascus, Antioch and Jerusalem.
Twice, Islamic armies reached the outer walls of Constantinople.
And as the Byzantines brooded on why God might have switched sides, they made a connection.
A big difference between Islam and Orthodoxy.
Muslims never make a picture of the divine.
The holy book of the Qur'an forbids Muslims to make images of the sacred.
The divine cannot be represented.
And Muslims were winning campaigns against the Byzantines.
Put two and two together, Christians, like Muslims, must destroy their images to win back God's favour.
And so, with the survival of his empire at stake, the Emperor Leo III
ordered the wholesale removal of icons from all Byzantine churches.
At the present day of course, the Ecumenical Patriarch of Constantinople
presides over a church rich in icons.
His own Church of St George is full of them.
So what brought icons back?
It was clear that, in destroying them, Leo was asking for trouble.
Riots broke out across the Empire.
It was a full-scale backlash.
Amid argument and violence, iconoclasm was born.
The word means "smashing images".
It was one of the great traumas of Christian history,
and it soaked up energy in Byzantium for more than a century.
Painting or venerating icons led to torture, sometimes death.
And many were prepared to die rather than see their churches stripped of this divine gateway to God.
It was an Empress, Theodora, who at last stopped iconoclasm in the year 843.
She commissioned a new liturgy, The Triumph Of Orthodoxy.
It acclaims those who defended icons and it gleefully names their enemies.
So the very worship of the Church enshrines the memory of that traumatic century.
The violent reaction to Iconoclasm demonstrated that Orthodoxy was not just a religion of the powerful.
It was the possession of ordinary people too.
Future rulers would forget that at their peril.
Right at the heart of Istanbul is a last word from the defeated iconoclasts.
The 8th-century Church of Holy Peace, Hagia Irene, built by an iconoclast Emperor.
Now it's a concert hall, stripped of nearly everything from its Christian past.
Except for a heart-stopping remnant from the fleeting era of iconoclast Orthodoxy.
Up in the apse, at the far end, over the altar, a simple black cross in mosaic against a gold background.
And that is iconoclastic art.
That is what the iconoclasts put in their churches.
You don't see this very often.
800 years after the death of Jesus,
Christianity was still expanding across the known world and beyond.
The Church of the East was established in the Middle East,
spreading its message from Baghdad to the far ends of Asia.
The Western wing of the Church, the Latin Church based in Rome,
was reviving and sending missions south, west and north.
And sandwiched between them was the Orthodoxy of the Byzantine Empire.
The Byzantine Empire might be battered and bruised,
but it was still the world's largest Christian power.
It had survived both Islam and iconoclasm.
The Church of the West and the East were still united
and the West had welcomed the defeat of iconoclasm,
which had always horrified the papacy.
But in practice, the gulf between Rome and Constantinople was deepening.
Whilst the Orthodox had been arguing about iconoclasm, an ambitious ruler had united
most of what are now France, Germany and Italy into a new Latin Empire.
Western Christians celebrate him as Charlemagne, Charles the Great.
Not the Orthodox.
Charlemagne sent Catholic missionaries to convert non-Christian
Slavs in the no-man's land between his Empire and the Byzantine Empire.
What was worse for the Byzantines?
Central Europe full of unconverted souls ripe for hell,
or central Europe full of devout little Catholic Christian Slavs
all grateful to Charlemagne? Something must be done.
The race was on to see who could get the Slavs to Heaven the quickest.
East or West?
Today Velehrad is in Roman Catholic territory,
and this is an overwhelmingly Catholic celebration of Slavic Christian heritage.
But it wasn't always so.
The men embroidered on those stoles are heroes of Orthodoxy.
Cyril & Methodius.
And they stole a march on Charlemagne's missionaries in what was then Great Moravia.
Because the crucial question arose of which language the Slavs should worship God in, Greek or Latin?
And Cyril and Methodius brilliantly outflanked the Latins
by answering the question with "Neither!"
The Slavs could worship God in their own language.
But now another problem.
Slavonic languages had never been written down.
Cyril and Methodius had an answer to that too.
This is the answer to the problem - an entirely new alphabet with symbols
completely unlike Greek or Latin because they're meant to represent the sounds of Slavonic.
But actually it was extremely difficult to use,
so someone decided to start again with characters much more like Greek.
But with exquisite tact, whoever it was, named their alphabet after Cyril - Cyrillic.
And it's the alphabet still used by the Russians, the Bulgarians and the Serbs.
Cyril and Methodius were getting the Slavs to worship in the language which they used in the marketplace.
That's what I find most astonishing.
The cliche about Orthodoxy is that it's timeless,
ultra-conservative, unchanging but this was innovative, creative.
The great contribution which Cyril and Methodius made to Orthodoxy
was to equip it to stay Orthodox in a rich variety of cultures.
Eventually even some which were not Slav at all, like the Romanians.
This would prove absolutely vital for Orthodoxy's long-term survival.
But the immediate result was bitterness.
Competition between Latin and Orthodox missionaries
in central Europe underlined the growing distance between the two wings of the old Imperial Church.
For the first thousand years of its existence,
the Church in the former Roman Empire had managed more or less to keep the appearance of one Church.
The Orthodox emblem on the headquarters of the Patriarch in Istanbul is the double-headed eagle.
One head for East, one for West.
I don't think that it's coincidence that Byzantine Emperors started using this symbol around 1000 AD,
just when unity between the Eastern and Western Churches was draining away.
Separated by geography, language and culture, East and West had been drifting apart.
There was in particular a little matter of words,
in fact one little Latin word - "Filioque".
It means "and the Son".
The Filioque was a tiny, Western addition to the Nicene Creed
which is a creed held in common between the Western and the Eastern Churches.
It says the Holy Spirit proceeds from the Father,
but the Court of Charlemagne in the 9th century added "and the Son".
The Holy Spirit proceeds from the Father and the Son.
This was the source of both tension and then crisis for centuries.
That one word, "Filioque", escalated East-West tensions.
The Byzantine Church felt ANY change to the Creed was blasphemy.
This was not going to end well.
The crisis point came in 1054.
Envoys from the Bishop of Rome arrived in Constantinople to deal with the growing rift.
They were spoiling for a fight.
Matters came to a head in the middle of the liturgy in Hagia Sophia.
The Cardinal from Rome lost his temper
and took it upon himself to excommunicate the Patriarch of Constantinople.
The Patriarch reciprocated.
At the time, this melodrama in Hagia Sophia seemed just a passing diplomatic spat.
But nearly 1000 years later, the schism between the Latin West and the Greek East has never been healed.
And within 200 years any chance of reconciliation
was given a final, fatal blow in one of the most shameful episodes in Christian history.
HE SPEAKS IN A FOREIGN LANGUAGE
In the decades following the Great Schism the Byzantine Empire was once more at the mercy of Muslim armies.
The Byzantines swallowed their pride and appealed to Western Catholic leaders for help.
And so in 1095 Pope Urban II launched the first of many Crusades.
The Latin Christian soldiers of the Fourth Crusade turned out to be less interested in defending the Holy Land
than in their own wealth, power and glory.
In an astonishing act of betrayal, they attacked the very people they were supposed to protect -
Christian Constantinople.
The Crusaders broke through the walls in spring 1204.
Thousands in the city died before it fell.
The known world's wealthiest and most cultured city was comprehensively trashed.
And the rape of Constantinople was carried out not by Muslims as the Byzantines had always feared...
..but by Catholic Christians.
If 1054 had marked the formal separation between East and West,
then 1204 was the gut-wrenching emotional point of no return.
Constantinople was occupied by Western Catholic carpet-baggers for 57 years.
But even though Orthodoxy snatched back its city, the empire never recovered.
For the first time, the Orthodox Church stood alone.
Western Christianity had broken Byzantium's spirit
and now another great power would finish the job.
During the 15th century, the Ottoman Turks ruthlessly gobbled up the Byzantine lands.
Soon all that was left was the once great city of Constantinople,
now a collection of shrunken villages,
with Hagia Sophia still looming over them all.
Ottoman besiegers snatched their chance.
On 29 May 1453, the Ottomans poured into the city.
In Hagia Sophia morning service bravely carried on
while the Turks battered down the great door reserved for imperial processions.
The Sultan gave orders that Muslim prayers be chanted out from the grand pulpit.
Hagia Sophia had become a mosque!
It was a savage end to the long Christian history of the Byzantine Empire.
Now all the strongholds of Byzantine Orthodoxy were under Muslim control,
including four of the five ancient Patriarchates.
Only Rome was free and Rome was not Orthodox.
For the next four centuries and more,
Orthodox Christians were second-class citizens
in the lands that their Emperor had once ruled.
In the mid-15th century, Orthodoxy might seem to be fated to be pushed into ever-narrower confines,
like the Church of the East or the ancient Churches of North Africa.
But remember that mission of Cyril and Methodius back in the 9th century?
Now that came to the rescue of the Orthodox future.
Cyril and Methodius had established a lifeline for Orthodoxy in Moravia.
Over the next 500 years, its spread north was to prove vital in this new crisis.
Orthodoxy's future now lay far from its origins in lands of an entirely different character.
Its people lived in the darkness of harsh winters, in communities often tiny, and widely separated.
Orthodoxy didn't just survive, it flourished,
moving out of the work of Cyril and Methodius east to Kiev,
encompassing everything we now think of as Russia to the frozen wastes of the Arctic in the far north.
Ordinary people took to Orthodox Christianity
with a fierce commitment that shaped and even defined a Russian identity.
Their faith was brought to them by lone individuals, wandering hermits
and holy men who sometimes settled in small communities.
And gradually over two centuries you had a great scatter of monasteries,
perhaps 100 or more, all over what is now northern Russia.
But still there would be holy men wandering beyond those communities
and that really is what rooted Orthodoxy in the people.
These ordinary men getting close to those scattered, lonely people over that vast territory
made Orthodoxy people's religion.
But this people's religion was also inextricably linked with the rise of what became the Russian Empire.
Its rulers learned to use the Church to expand and control the Empire
and make their rule sacred.
The Orthodox Church came to be at the centre of a three-way tug of war between the ambitions of the Tsars,
the clergy and the devout faith of the Russian people.
During the 14th century, as holy men and women spread Christianity amongst the people,
the rulers of a modest settlement with big ideas
were quietly turning themselves into a power you couldn't ignore.
The settlement was Moscow.
And the ruling dynasty fashioned itself as heir of the Byzantine Empire.
Just to make sure of its claim, in 1472 the Grand Prince of Muscovy,
Ivan III, married the niece of the last Byzantine emperor and he adopted
the double headed Byzantine eagle as his symbol and just occasionally he used the title "Tsar"
which is simply the Roman imperial Kaiser, Caesar.
The first Rome had fallen to barbarians and sunk into Roman Catholic heresy.
The second Rome, Constantinople, was now in the hands of Islam.
The Orthodox Church of Russia now seized the title "the third Rome".
Eventually it even gained its own Patriarch in Moscow.
But though Russian Orthodoxy's origins were in Byzantium, the rule of the Tsars
and the intense religion of its people created a Church which was distinctively Russian in character.
You can see that straightaway from a short walk through Moscow.
Russia's church domes took on the shape of an onion.
Some think the design was inspired by manuscript pictures of the Church of the Holy Sepulchre in Jerusalem.
Others see it as just practical.
A way of stopping the build-up of snow.
Either way, the design redrew the Russian landscape.
The most famous of these churches was built in the 16th century...
..St Basil's Cathedral in Moscow's Red Square.
Its exterior is startlingly original.
An eight-sided central church rising into a spire, hemmed in by eight smaller churches.
Do you remember how Byzantine Orthodoxy looked to one great church in Constantinople?
The Holy Wisdom had been built by a great Emperor and military commander, Justinian.
Well, you could say that this church was intended to do the same thing for Russian Orthodoxy.
The only problem was that it was built by the maddest, cruellest emperor in world history.
Ivan the Terrible placed St Basil's in the centre of Moscow in 1552.
And like Justinian 1,000 years before,
he made his church the centrepiece of his Russian Orthodox Empire.
Of course, Ivan is better remembered for persecuting and butchering millions of his subjects.
And inside St Basil's you get an idea of his mindset.
If you look at it on a plan it looks perfectly rational
and symmetrical but no-one ever did see it in plan apart from the architect and the patron.
Your actual experience of it, once you're inside, is a combination of vertigo and claustrophobia.
I don't think that it's too much to say it feels...deranged.
In Russian, the word "terrible"
is better understood as "awesome"
but the English translation "terrible" gets Ivan just right.
Born in 1530, he was crowned at the age of only 16, as the first Tsar of Russia.
And this gave him ideas about the Orthodox Church.
He became obsessed with making Russia holy Russia,
with himself at the centre as God's representative on earth.
Early in his reign he was full of energy, building churches,
ordering exact rules for how icons should be painted.
That concern for holiness was not necessarily a bad idea, but it was perverted into tyranny.
During his 37-year reign,
Ivan exercised absolute power through atrocities on an insane scale.
And he clearly came to love terrifying and hurting people, just because he could.
And yet the metropolitan bishop of Moscow who crowned him left him with a terrible sense of sin.
Ivan once cried out in a letter, "I, a stinking hound,
"whom can I teach, what can I preach, and how can I enlighten anybody?"
Ivan's concern for the welfare of his soul was amply justified.
His religious despotism reached deep into the lives of his subjects,
as he dictated how Orthodoxy should be practised down to the minutest detail.
Not even men's beards escaped his judgment.
For Ivan, the beard was an ornament given by God to Jesus,
so he forbade the shaving of beards.
And heaven help anyone who went against him.
Ivan was convinced that God had made him Emperor when the Metropolitan crowned him.
So that anyone who opposed Ivan was a heretic and deserved the punishment of death,
preferably in as nasty a way as possible.
In the worst years of his reign, Ivan enforced his crazy tyranny across the Empire through the Oprichniki...
..a perverted version of a religious order,
robed in black cloaks as they went about their inhuman business.
Millions of Russians were killed in Ivan's purges.
And yet one man dared to stand up to the tyrant.
And St Basil's Cathedral is now named after this hero of humble Orthodox faith.
St Basil was a very particular, peculiar sort of hermit - a Holy Fool.
Holy Fools overturned all the rules of normal society.
They behaved like madmen to show the power of God.
And St Basil showed that very well because he was one of the very few people
who could stand up to Ivan the Terrible and get away with it.
In the middle of Lent, the saint once thrust some meat into the hands of the astonished Tsar,
telling him that there was no point in him trying to fast since he had committed so many crimes.
Ivan was humbled, St Basil unpunished.
St Basil's story is the perfect reminder of a repeated keynote in Russian Orthodox history.
The depth of faith among ordinary Russians was so profound that whatever the Tsars did to them,
they obstinately continued to worship in their own way.
Religion was woven inextricably into the fabric of ordinary life,
often in alarmingly eccentric ways, as in the case of the sect known as the Skoptsy.
Well, they were devoted to eliminating sexual lust from humankind
by cutting off their genitals.
Their founder had read his Russian bible but he'd misread it.
He read the word for Jesus the Redeemer, "iskupitel"
as "oskopitel" - castrator.
A century after Ivan the Terrible, another Tsar came up against that strength of feeling
with bloodstained results.
Tsar Aleksei and his Patriarch both wanted to tidy up the Church,
take it back to a pure Byzantine Orthodoxy.
Take sacred blessings, for instance.
In the Byzantine tradition, clergy made the sign of the blessing
using three fingers to symbolise the Trinity.
But in Russia, two fingers were used to symbolise the two natures of Christ.
Now, Aleksei ordered Russian clergy to change the sign of the blessing to three fingers.
It might seem utterly trivial to us but in that world, every detail mattered.
Your average Russian couldn't care less about being faithful to Greek Orthodox tradition.
They knew what Orthodoxy was - it was Russian.
And this was heresy.
So thousands, eventually millions of them, defied the Tsar.
Some left the Tsars' Church and became known as "Old Believers."
Many were burned at the stake for their defiance.
And some, rather than submit to the Tsar's heretical authority, actually set fire to themselves.
The Imperial Church was still there.
It continued to serve the people of this vast empire.
But between Tsarist autocracy and the lives of the people,
there was that third force -
the hierarchy of the Church...
and a question that even the Byzantines had never quite resolved.
Who was truly God's representative on earth?
The Tsar or the head of the Russian Church, the Patriarch?
In 1689, the throne of Russia was inherited by Peter the Great.
He settled that question for the next two centuries.
Where Ivan the Terrible had been mad, Peter the Great was rational.
But he was still a tsar.
He saw Orthodox Christianity as just another useful tool to control the Russian Empire.
And this is his statue - one of Moscow's latest tourist attractions.
It's widely hated in the city but I'm going to be unfashionable.
I rather like it. It's quite fun.
Peter astride his ship from his brand-new navy.
Peter was a moderniser and a big part of his modernising Russia was to seize control of the Church.
For nearly two centuries after his time there was no Patriarch.
The Church was run by a set of state bureaucrats.
So now the Church had lost control of its own decision-making.
There was now no question as to who was in charge -
the Tsar.
As usual, in Christian history, the Church made the best of it.
In fact, it prospered.
In the 19th century Russian monastic life flourished.
Churches actually got more crowded.
And at least the Church was safe.
Orthodoxy had survived a turbulent 1,300 years.
But its next encounter nearly wiped it out.
At the start of the 20th century,
Russia was a great European power under Tsar Nicholas II.
And yet by 1918 his world had been overwhelmed in the Great War and Revolution.
And in the thick of it all was a Russian peasant from Siberia...
..a wandering hermit who became the focus of a public scandal surrounding the Tsar's family.
The Tsarina believed that God spoke to her, through the hermit.
But his enemies said he was a lecherous drunk whose interference crippled the government.
In the last days of the Tsars, during the First World War,
Grigori Rasputin gained an extraordinary hold
over Tsar Nicholas II and his Empress
because he appeared to be able to stem the haemophilia of their son.
Was Grigori Rasputin a Holy Fool or a crazy drunk?
Well, perhaps he was both.
But his peasant faith made a fool out of the Tsars and helped to doom their regime.
Russia was descending into nightmare.
It was losing the war with Germany.
Its people were starving and turning to revolution.
And the Rasputin scandal became hugely symbolic,
a dose of poison for the Tsarist regime.
As hundreds of thousands died on the front, the troops voted with their feet and mutinied.
In February 1917 there was revolution.
The Russian Emperor was forced to abdicate, bringing to an end nearly 500 years of Tsarist rule.
For the Church, there was a brief moment of hope.
A liberal provisional government was formed, Russia's first real experience of democracy.
In Moscow a council of bishops, clergy and laypeople
made plans for a revived Church, free of Tsarist interference.
Triumphantly, they elected a new Patriarch, the first since Peter the Great.
But it proved to be a false dawn.
In October of that year, worldwide Orthodoxy met its most terrible enemy so far.
Soviet Communism.
With Lenin at its head, the Bolshevik Party seized the revolution
and installed a dictatorship of the proletariat, with absolute power over all Russia.
In this new world order there was no place for God.
Orthodoxy had shaped Russia since the 10th century.
But the Bolsheviks saw all religion as the opium of the masses,
a symptom of false consciousnesses and, worst of all, an obstacle to scientific socialism.
In January 1918, Lenin formally separated Church from State.
And that was just the first step in a systematic policy to purge Christianity
altogether from Russian life, and force atheism on its people.
But it was a policy Lenin did not live to carry out.
The task was followed through even more ruthlessly by a man who,
in just 10 years, brought Orthodoxy close to extinction -
something neither Catholic crusaders, Muslim armies, nor Russian tyrants
had managed to do in 1,000 years.
Joseph Stalin was a Georgian gangster
whose mother had once hoped he would become a bishop.
Instead, he had manoeuvred his way up through the ranks of the Bolshevik party
to become supreme ruler of the Soviet Union.
A red tsar, one might say.
His plan was to wipe out all real life in Orthodoxy.
In a society without God there was no need for churches.
This is the dynamiting of Moscow's Cathedral of Christ the Saviour in 1931.
Then there were the human victims - the Orthodox faithful.
Around 40,000 priests and 40,000 monks and nuns,
plus millions of laypeople died as a result of Soviet terror.
There was a manic thoroughness to the campaign.
Some local Soviet commanders lined up icons, sentenced them to death and shot them!
By 1939 only a few hundred churches remained open
and only four bishops were not in prison.
And yet Russian Orthodoxy survived.
In the Second World War, Stalin was forced into a remarkable U-turn.
Stalin needed the Church's support to win the war.
And in order to use the Church, he needed to recognise the Church.
It was Orthodoxy's patriotism that saved it from extinction.
Stalin had to accept that for many Russians
it wasn't the state that embodied Russian culture and national feeling...
it was the Church.
And so he allowed churches, theological schools and monasteries to reopen.
But after the war, it was Soviet business as usual. More persecution.
At the end of the Second World War, Soviet rule gripped most of Eastern Europe.
When Stalin died in 1953, Russia was a world superpower.
And for the next 30 years it held Orthodoxy prisoner.
Yet the Orthodox Church kept its faithful followers,
maintained its ancient liturgy and music through all the traumas inflicted on it by the Soviet Union.
Indeed, Orthodoxy outlived the communist world order.
When General Secretary Gorbachev tried to implement a more humane communism, "glasnost,"
it turned into an endgame for the system.
By the 1990s it was all over.
All the emotional power had drained out of state communism.
And nothing showed that more than the moment in 1991 when a crowd toppled this statue, that of Dzerzhinksy,
the architect of the KGB system, which is now relegated to a quiet park -
a sort of retirement home for tyranny.
For 70 years, the Soviets had told their subjects that communism was the future.
Now communism had gone.
What was compelling enough to fill that gap?
Orthodoxy.
It has triumphantly seized back its place at the heart of Russian life.
In the 1990s, money poured in from the public
for the rebuilding of the Cathedral of Christ the Saviour in the centre of Moscow,
the Cathedral which Stalin had obliterated 70 years before.
In its sufferings, Orthodoxy survived catastrophes
quite unlike those faced by Catholicism and Protestantism.
Stripped of the power it knew under the Byzantine Emperors,
it saw its freedom stolen by the Russian Tsars,
its people nearly all expelled from Asia Minor,
its very existence nearly destroyed by the Bolsheviks.
But in 21st century Russia, the double-headed eagle of Byzantium
has once more became the proud emblem of modern Russia.
There is still a legacy for the Eastern Roman empire.
But solve one question, and another appears.
Can Orthodoxy survive its first meeting with Western freedom?
The world of capitalism, consumerism, scepticism and sexual freedom?
So far, the instinct seems to have been to reaffirm old certainties.
And you can understand why, if you think back to all those places I've been.
The solemn unfolding of the liturgy, the serene gaze of the saints,
the experience of God in wordless prayer.
And yet for all that, Orthodoxy may still have to learn from western Christians
how to cope with new challenges, which western Christianity itself has helped to create.
So, in next week's programme, we're turning west again.
We're going to see how the great monarchy which was the medieval Western Church
split in two in the Reformation.
And then we'll go on to meet the forces of the modern world,
from which no Christianity of the 21st century can now hide.
Why not take part in the Open University's online survey,
"What does it mean to be a Christian today?" At -
And follow the links.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk