I'm Jonathan Phillips, a history professor at the University of London.

When my studies took me into the world of early Christians, I realized that nothing captivated my imagination like their struggle to bring a fragile new faith into the world.

I embarked on a journey of a lifetime, taking me 12,000 miles to follow the story of the first Christians.

In our last episode, we witnessed the Apostle Paul's return to Jerusalem, braving warnings of mortal danger.

We saw those warnings prove true as he was attacked by an angry mob and arrested by Roman soldiers.

Paul was sent by sea toward Rome to be imprisoned there by the deranged Emperor Nero.

Soon Rome burned.

Paul, the Apostle Peter, and thousands of fellow believers were falsely blamed and martyred.

Now the city of Jerusalem will be rocked by war.

We follow the terrible events of the Jewish revolt, and we see how this affected the fragile growth of the Christian faith.

Then we'll explore the remote island of Patmos.

We'll see the cave where tradition holds the voice of Jesus spoke to St. John, bringing him and the world the most enigmatic and controversial book in the New Testament, Revelation.

Finally, we'll follow the story of Christianity as it faces some of its greatest challenges from heresies whose radically different views of Jesus and his message would pose a dire and divisive threat to the faith.

Having traveled extensively in Asia Minor, Greece, and Rome, I must return to Jerusalem.

Behind me is the magnificent sight of the walled city of Old Jerusalem, a location of spiritual intensity unparalleled anywhere in the world.

During the first century, Jerusalem was flowering as a cultural and commercial center.

Yet it was also on the brink of disaster.

Resentment had long been festering among the city's Jews against the Roman occupiers and the Herodian puppet kings.

The judicial murder of the Apostle James was a significant point in the history of Christianity, Judaism, and the city of Jerusalem.

James was the most powerful man in the community of Christian believers in Jerusalem.

He was also held in high esteem by many within mainline Judaism.

James's unexpected and savage death put the Christian community in disarray.

Safe to the north in Greece and Turkey, the churches established back in Paul's day were protected by geography and by the growing separation from Judaism, but to the south in the Holy Land, storm clouds were gathering as tensions built.

To make matters worse, Emperor Nero's mental instability resulted in a lack of direction from Rome.

This added to the turmoil and brought the city closer to the brink of chaos and calamity.

Josephus, who would later become a Jewish general and a historian, personally witnessed the turmoil in Jerusalem.

PHILLIPS: Chaos was building in Jerusalem.

The powerful oppressed the masses with huge taxes.

Resentment grew and grew.

Unlike Paul's congregations, the Christians in Jerusalem still followed Jewish law and still saw themselves as Jews.

After the death of their leader, James, many joined the growing Jewish opposition to Roman rule.

Tensions were high, and violence was becoming inevitable, unleashing a struggle that would change Christianity and Judaism forever.

Jewish protests at ever greater Roman greed grew increasingly violent.

In the year 66, rebels killed the high priest Ananias, whom we met earlier as a persecutor of Paul, for colluding with the Romans in seizing money from the temple.

The land of Judea was in chaos, and in many cities, fighting broke out between Jews and Gentiles, too.

Rome needed to assert its authority by force.

The Jews wanted their freedom.

Both sides prepared for war.

The superior Roman forces soon subdued most of the land, leaving Jerusalem, the Holy City, as the focal point of resistance.

Archaeologist Avner Goran told me about the destruction of the Jewish temple.

But why were the Romans breaking this place up?

PHILLIPS: Right.

PHILLIPS: Starting in the year 66 and lasting for seven years, the Jewish-Roman War was a brutal, brutal struggle.

When the Romans, now under Titus, finally reached Jerusalem, they used every tree for miles around to build a massive wooden stockade that completely surrounded the city, stopping all escape.

Cut off from food, the Jews began to starve, and any that tried to escape or find food outside the city walls, as many as 500 a day, were stopped short by the Romans, captured, and crucified in full sight of the city's defenders.

When the Romans finally overran Jerusalem, they killed virtually every surviving inhabitant -- men, women and children.

They also burned the Jewish temple to the ground, not leaving one stone upon another.

Then they looted, stripping the city and especially the temple of its incredible wealth.

PHILLIPS: In the end, Jerusalem lay in ruins.

[ Goran speaking ] PHILLIPS: While the temple itself was reduced to ruins, a retaining wall that supported the Temple Mount was left standing.

Down to our left, we can see the Wailing Wall, which is obviously a focus of enormous religious devotion.

Was that always the case?

PHILLIPS: So it was simply an external barrier?

PHILLIPS: So sort of the magnet has moved, is what you're saying.

[ Goran speaking ] PHILLIPS: Right.

PHILLIPS: The Wailing Wall was on the western side of Temple Mount.

After the temple was destroyed, this section of the wall became such a significant religious monument because it is considered to have been the closest to the Holy of Holies, the most sacred part of the Jewish temple.

The sack of Jerusalem, the serious dislocation that resulted from it and would continue to result over a period of decades after that event, forces all kinds of Jews, including the followers of Jesus, to try to make sense out of how it could have gone so massively wrong and where do we go from here?

"But from its first building till this last destruction were two thousand, one hundred and seventy-seven years..." This is largely when at least one large component of Christian thought begins to move in a more metaphorical, rather than literal or political, way of interpreting the actual teachings of Jesus regarding the kingdom of God.

PHILLIPS: The next stop on my journey is Patmos Island, where events took place that would have a profound effect on Christianity.

Tradition holds that the last living apostle, John, was forced into exile here on Patmos.

Located in the Aegean Sea, it can only be reached by boat.

[ Speaking Greek ] In the first century after Christ, the island of Patmos was an ideal spot for the Roman Empire to send dissident political agitators.

St. John's years in exile would have a tremendous effect on Christianity, because he or a namesake is held to be the author of the Book of Revelation.

This is surely the most startling volume in the New Testament and a work that's still controversial and subject to many different interpretations today.

John wants to say to his audience, for whom he writes this extraordinary book, "You must have nothing to do with this Roman pagan culture.

"The faith that we embody in what we do "is something which is counter to everything that the world, so called, stands for."

High on a ridge behind me stands the Monastery of St. John, founded by Greek Orthodox monks in the year 1088 here on the island of Patmos.

It has stood there for centuries, resisting the attacks of Turks and pirates alike.

It guards the memory of St. John, author of the Book of Revelation, and to me its fortress-like exterior seems suited to a book of such extraordinary and at times violent moods.

Yet, at the same time, of course, the interior has managed to maintain the calm and sanctity of a monastery.

TAYLOR: He wants to say to the Christian communities for which he writes to stand up for Christianity and to stand against paganism even if it means that you're going to lose your life.

That is the cost of what it means to be Christian.

PHILLIPS: Below the monastery is St. John's Cave, where tradition says he lived and wrote down Revelation.

The cave has been preserved for over 18 centuries and is now visited by thousands of pilgrims each year.

[ Speaking Greek ] PHILLIPS: I met with Archimandrite Antipas, who is in charge of St. John's Monastery on Patmos.

Could you tell me what happened in the cave?

[ Speaking Greek ] INTERPRETER: The cave is important because this is where God delivered the revelation to John the Evangelist.

There was an earthquake on a Sunday, and at the same time lightning and thunder, and you can still see on the walls of the cave the split in the rock.

Nonetheless, God did not want to scare John and John's pupil, who were together in the cave.

So God's voice was melodic.

God spoke in song.

John listened entranced, and his pupil wrote down the words of God.

PHILLIPS: This is the tremendously atmospheric Cave of St. John on Patmos.

This crack in the ceiling here is believed to be the spot through which Christ's message appeared to John.

And over here is the place where he would lay his head when he slept.

Here is the place he put his hand where he prayed.

Behind it we've got this pretty magnificent image showing the whole story from the start of the Book of Revelation.

Christ, here holding the keys to the kingdom of heaven, is appearing to John, who is sleeping down there.

Christ has also got seven stars and these seven candlesticks, which represent the seven churches of Asia, the people to whom his message was directed.

The book of Revelation begins with seven messages spoken to John, to be delivered to seven churches in Asia Minor.

They were words of encouragement as well as words of caution.

One example is found in the message directed to the Church of Ephesus.

ANTIPAS: [ Speaking Greek ] INTERPRETER: In the Middle Ages in the West, the idea took hold that the Book of Revelation is a book of terrors.

We in the East see it rather as a book that teaches modesty, self-awareness, faithfulness, and love.

It is a difficult book to interpret, and parts of it defy interpretation, but on many points it is realistic.

It has universal validity across cultures and nations.

It's important to remember that apocalyptic is not just the Book of Revelation.

It's a very wide phenomenon, and it happens across the ancient world.

There are Jewish apocalypses.

There are Christian apocalypses.

There are Roman apocalypses, Greek apocalypses.

So it's a phenomenon that takes place across the ancient world.

But it does have certain things in common, and one of the things that it does use very often is weird and wonderful and wild imagery.

The only way we can really understand the Book of Revelation is by seeing it addressing its own audience in its own day.

And we make a mistake if we think that the imagery is meant to be taken literally.

John certainly didn't understand it in that way.

Neither would his readers have done so.

They would have been familiar with what we call today "apocalyptic literature."

Now, "apocalypse" literally means "a revelation, an unveiling."

Of course, the way John does this is through this book of extraordinary imagery.

You know, we find these images of star-crowned women.

The Jesus in the Book of Revelation appears as some kind of fiery individual.

His eyes look like they're on fire.

We have strange images of slaughtered lambs.

We have wicked kingdoms represented by prostitutes bearing big bowls of blood.

And then we have this final image of a new Heaven and a new Earth which arrives to redeem it all.

But the ultimate message is, "Don't accommodate yourself "to the society of the day.

"Resist, stand up to it, "because the only one you can really trust is God, and God will bring you through."

The Book of Revelation really is a kind of, a piece of dynamite within the Christian movement itself, trying to fracture that sense of, "We can be part of the Roman world."

PHILLIPS: It's a rallying call.

WHITE: It is both a rallying call, it's a gauntlet being thrown down.

In the final analysis, it says, "If you Christians" -- and it's speaking to Christians -- "If you Christians think you can worship the Emperor, you might as well be worshipping Satan himself."

That's the point of the Book of Revelation.

PHILLIPS: John's message brought a warning to the beleaguered Christians.

But it also brought a badly needed message of hope -- regardless of the tribulations they faced in the here and now, in the hereafter there would be a heavenly paradise.

Christianity was at a dangerous crossroads.

Not only was its future course uncertain, but it lacked the leadership and structure to determine what that course would be.

Although it had spread across the Mediterranean, it still had a relatively small number of congregations, with no common leadership and little organization.

LYMAN: You would almost say each of these Christian groups find its own challenge in the particular city and you're engaged, really, in the second century, in a whole system of identity building, figuring out who you are as a Christian.

But I think the theological reality is, because you have this historical mission and diversity, unity is then a concern that you have.

How do you contain these various groups?

How are they different and yet the same in what they share?

PHILLIPS: Its future would lie in the hands of a new generation, a generation of men who had met and learned from the original twelve apostles.

Their task -- to organize, to define, and to protect the fragile faith.

Like the apostles, though, they too were often the victims of persecution.

The next stop on my journey will be the city of Smyrna, now called Izmir, on the west coast of Turkey.

Polycarp, one of the most important of this new generation, called Smyrna home.

As the generation of apostles passed on, the torch was taken up by their disciples.

In the case of John, here in eastern Asia Minor, his work was sustained by Polycarp, the Bishop of Smyrna, then as now a thriving port and today the huge Turkish city of Izmir.

Izmir is still a bustling hub, much as it was in Polycarp's day.

Known then as "the ornament of Asia" for its beauty and splendor, Smyrna prospered because it straddled key trade routes and had the best harbor in the region.

As good Roman citizens, the people of Smyrna worshipped the Roman emperors as gods.

Within Roman paganism there is no distinction between religion and politics.

The emperor is the head of the religion, just as he is the head of the state.

The idea of the imperial cult, the idea that the emperors are themselves in some sense gods.

In fact, during their lifetimes an emperor was not worshipped as a god within Rome.

Instead they were the Pontifex Maximus, the chief priest, the greatest priest.

When an emperor died, he became divine.

The imperial cult honored the emperors.

PHILLIPS: Smyrna was dedicated to the cult of emperor worship, yet this was something that the Book of Revelation had explicitly condemned.

It was a real challenge for Christians to live up to this, and in as staunchly a Roman city as Smyrna, Christians such as Polycarp who refused to participate in these rituals faced violent persecution.

Faced with the horrifying prospect of death by wild animals or fire, some, quite naturally, perhaps, weakened in their faith and chose to deny Christ to save their skins.

In the case of Polycarp, however, the man after whom the church beside me is named, the sentence of death held no such fear.

After several Christians had just been horribly tortured and killed in Smyrna's arena, bloodlust filled the air.

[ Growling ] The crowd demanded the death of the 86-year-old Christian leader, Polycarp.

To placate them, the city's proconsul had Polycarp brought to the stadium for judgment.

There he was offered his life if he would worship Caesar.

Polycarp refused.

"This man is the destroyer of our gods," bayed the crowd.

The aged bishop was sentenced to be burned at the stake, but when the fires were lit, the flames curved around Polycarp like a ship's sail filled with wind.

He remained unscathed.

In the end, a Roman soldier killed him with one thrust of his weapon.

Nearby, a friend and colleague of Polycarp would also refuse to renounce Jesus.

He too would pay the ultimate price.

Ignatius was appointed Bishop of Antioch by the Apostle Peter.

As I return to Antioch, now the city of Antakya, in southern Turkey, I'm struck by the important role this place played in the birth of Christianity.

It was here that Paul rebuked Peter over Jewish law.

It was here that Paul and his friend Barnabas argued and parted company.

It was here that Christ's followers were first called Christians.

As Bishop of Antioch, Ignatius played a key role in the growth of the early Church, but in the early second century, he was arrested and sent to Rome.

During the journey, he wrote a series of letters to the Christian communities of Asia Minor, urging them to hold true to their faith.

He also outlined one crucial and, for the time, revolutionary idea.

Instead of the loose gatherings of elders that tended to dominate Christian communities, he stressed the need for an individual bishop to lead the Christians of each city.

Thus he sign-posted the need to create hierarchy and structure, something crucial to the development and spread of the Church.

Thanks in part to Ignatius, the Church was beginning to divide its hierarchy to better address the secular as well as spiritual issues.

While priests were responsible for spiritual matters, deacons were beginning to take on the more secular role, but all under the supervision of the bishop.

PHILLIPS: When the Emperor Trajan ordered Ignatius brought to him, the Christian leader refused to renounce Christ and was sentenced to death.

Imprisoned in Rome, Ignatius penned a letter to local church leaders, asking them not to plead for his life and expressing enthusiasm for his upcoming martyrdom.

When the time came, Ignatius willingly entered the coliseum.

[ Lion roars ] He remained at peace as he was devoured alive by two ravenous lions.

Polycarp and Ignatius were just two of the greatest teachers of this period, men whose ideas encouraged, sustained, and directed early Christians and men whose martyrdoms inspired admiration in their followers.

As we move through the second century, Christianity has to confront another very significant challenge.

This time it comes from within.

Today we're used to a world in which Christianity has many different branches, many different denominations, something that has been the cause of terrible conflict down the centuries.

Yet back in the second century, as the scattered Christian communities began to establish themselves, perhaps we shouldn't be surprised they sometimes disagreed amongst one another as to who was within their community and who was not.

And this meant setting up boundaries.

In the second century, then, we -- Christians invent heresy.

I mean, "heresy" to begin with was simply a word that meant a sect.

It meant a choice of a philosophy in antiquity.

Christians take that word haeresis and turn it into "heresy," which we know as a negative term, which means a negative belief, an error, a chosen rebellion against a particular, particular order.

One of the great challenges to so-called orthodox Christian belief in its early years is Gnosticism.

PHILLIPS: The Gnostics believed that many contemporary Christians were distorting Christ's words, that Jesus' true message carried a secret knowledge, or gnosis, understood only by intellectuals and not the common person.

For that reason, the Gnostics' opponents saw them as smug, arrogant elitists.

This idea that you can be saved in two ways, really.

One is by removing yourself from the wickedness of the world, and the other is by some kind of secret, esoteric knowledge, and this idea somehow, therefore, that Jesus is saying to his disciples that if you follow my words, then you can achieve some kind of salvation.

And this was a difficult problem for the early Church, not least because one of the problems with Gnosticism is that it has a very low view of the material world.

The material world is a wicked, terrible place.

We need to be rescued out of it.

Our true life is somehow spiritual.

PHILLIPS: Like Christianity itself, Gnosticism became fragmented with alternative or competing interpretations.

This was a time that many different ideas emerged, such as Docetism.

TAYLOR: Docetism, the idea somehow that Jesus only appears to be human.

He puts on the kind of appearance of being a human being, but he's not really.

So he kind of wanders around, he's really God in the kind of disguise of being a human being.

PHILLIPS: Other interpretations that later became labeled as heresies included Marcionism, that rejected the Hebrew Bible and the God of Israel, believing the real God only arrived with the coming of Jesus.

Montanism believed that there should be no clergy, since all Christians could be prophets.

Female prophets accompanied Montanus, and his followers emphasized spiritual gifts and speaking in tongues.

Valentinism believed that salvation comes from gnosis, knowledge, and not from faith.

Cainians revered Cain as the first victim of the evil Jewish God, Yahweh, and believed his murder of Abel helped guide man towards redemption.

PHILLIPS: Explain to me Gnostic belief.

Well, that's a, that's a highly contested question, in part because for many centuries all we knew about the people who were called Gnostics were basically told by their opponents.

The word itself means someone who knows, someone who knows.

So in the literature written against them, they are seen as people who are arrogant, people who think they are smug.

They know more than other people.

They're not obedient to the faith.

PHILLIPS: The Gnostic heresies incorporated many of the dozens of gospels being written at the time.

They included the gospel of Thomas, Mary Magdalene, and even the gospel of Judas, presenting Judas as a helper, not an enemy, of Jesus.

LYMAN: You would see these as people who, in these communities that don't have necessarily strict boundaries, these are teachers, these are people doing different exegesis on the gospel stories, and therefore then writing different accounts.

The issues over the body, over, "Is the body evil?"

"Is human experience in history wrong?"

"Where does evil come from?"

"Does evil come from matter itself?"

"Was creation a mistake?"

These are, these are, you know, for those of us who like theology, these are great questions, you know, that have existential applications to the way that we would live our lives.

Who was right?

One way to limit these challenges, as Ignatius of Antioch had suggested, was to form structures and to give individuals power to decide on correct behavior or belief within each community and for the wider Church.

These men became known as bishops.

The battle for Christianity was entering the next phase.

Leading the fight was a man who lived here in this part of the Roman Empire, a region called Gaul.

I'm here in the city of Lyon, in central France.

What, you may wonder, does that have to do with early Christianity?

Many of the first Christians in the West, such as Peter and Paul, came from the East.

In the second century A.D., one such traveler became bishop in what is now France.

And this man would exert a crucial role in defining early Christianity.

His name was Irenaeus.

Born in Asia Minor, Irenaeus was a student of Polycarp.

He was only 16 years old when Polycarp converted him from paganism to Christianity.

He studied with Polycarp for 10 more years, then became priest here at the Church of Lyon during a time of persecution.

Irenaeus was determined to defend the Christian Church against the so-called Gnostics, a group who believed they had special knowledge of God.

Irenaeus, by contrast, asserted the superiority of faith over knowledge.

Irenaeus became bishop of Lyon in the year 177 A.D., after a massacre of the Christian community.

Forty-eight members of one small church community were killed in this ancient Roman stadium.

The killing occurred under the Emperor Marcus Aurelius, but it was not the emperor who ordered this.

Instead, like so many attacks on early Christians, it was local hostility towards the new religion which provoked this terrible assault.

By the time of Iranaeus, no Christians were still alive who had known the disciples or their first converts.

The Christian message, Iranaeus declared, must be defended by bishops, such as himself, who would preserve the teachings of the disciples through the principle of apostolic succession.

Irenaeus successfully refuted the ideas of the Gnostics, embracing only the gospels of Matthew, Mark, Luke, and John.

TAYLOR: What he wants to say is that these gospels represent the four images that we can have of Jesus in the same way that we live in a world which has four directions -- north, south, east, and west; we can also echo the four beasts that you find in the Book of Revelation; there are also the idea of the four different covenants that God made with his people through four individuals -- Noah, Abraham, Moses, and Christ; and also the idea of four principal winds that blow through the world.

But that's what Irenaeus left us with, four gospels like that, but that's not to say that there weren't other writings that were competing for attention at the same time.

There's the gospel of Thomas, the gospel of Mary, gospel of Peter, which again we would see as various versions of the Christian story.

PHILLIPS: In his book "Against Heresies," the gospel of John was regarded as more spiritual than the three gospels of Mark, Luke, and Matthew, which are considered synoptic gospels because of their similarities on the story of Jesus.

TAYLOR: What they share really is in large measure the same kind of sets of themes and ideas, and what is true of all three of the so-called synoptic gospels, Matthew, Mark, and Luke, is that they are just as theological in their intent as they are anything else.

What makes a gospel a gospel?

And perhaps one way of getting hold of that is by thinking of the difference between, say, a photograph and a portrait.

When you have a photograph, you have something which is really quite fixed, in a way.

It's not really open to lots of interpretation.

A portrait, however, is open to all kinds of ways of viewing, ways of being interpreted.

The gospels are really more like portraits than they are photographs, that they give us pictures of Jesus and of what he was doing and saying, but they are still today open to endless kinds of interpretation, whichever way you want to look at it.

PHILLIPS: As Christianity continued to expand, so did the war between mainstream Christianity and the Gnostic heresies.

As I continue my journey through early Christianity, I will go to where the battle over Christianity's future would take place -- a battle fought not with arrows and swords, but ideas and beliefs -- northern Africa.

In centuries past, the north African city of Carthage was Rome's most dangerous rival, and, led by the great general Hannibal, the city's armies conquered much of northern Italy, even threatening Rome itself.

But Rome defeated Carthage, and eventually it became one of the most important and prosperous cities in the Roman Empire.

One man whose thinking would have a lasting impact on Christianity lived here in Carthage.

His name was Tertullian, born to pagan parents in the year 160.

Following his conversion in mid-life he became a prominent leader in the Carthage church and a prolific orator and author in both Greek and Latin.

We have this prolific, funny, acerbic writer, Tertullian, who writes on, "Should women be veiled?"

"Should you go to the games?"

"Can you be a soldier and be a Christian?"

I mean, he writes a vast amount of literature that there's obviously a lively Christian community going on there at the time.

PHILLIPS: His writings, known as apologies or defenses, also paint the picture of the early Christians as charitable and caring Roman citizens who gave aid not only to each other, but to anyone who sought help, including pagans.

The ancient pagan world had little tradition of caring for the poor and unfortunate.

Wealthy Romans could and did give money to aid those less well off, but these actions were celebrated for glorifying the giver more than for aiding the recipients.

The emphasis on welfare and on caring for others for their own sake is one of Christianity's greatest legacies to the modern world.

Charity is one of the key features of Christianity.

Now, in a world where people suffer, that is going to attract converts.

In a time of plague, Christian numbers grew even as the population failed, because Christians looked after each other.

We have stories from Carthage in north Africa of Christians working in hospitals, creating hospitals, where they cared for anyone who came to them.

PHILLIPS: Tertullian offers one of the very few examples in the ancient world of the care for the poor and orphans for their own sake.

"Every man once a month brings some modest coin "or whenever he wishes, and only if he does wish, and if he can.

"Nobody is compelled.

"It is a voluntary offering.

You might call them trust funds of piety..." LYMAN: One of the ways to look at Christianity, it drew in people from different ethnicities and different social classes.

What's interesting about it is it does have a mixture of people in it who are not necessarily used to being with one another, in terms of different classes or different ethnicities, slaves, freedman would be in the community, and that could also contribute to the volatility of it, that suddenly I'm sharing table fellowship with people I wouldn't normally meet in my Roman stratified society.

It's part of that idealism of that sectarian, charismatic community in the second century.

As the empire declines, Christians pick up more of the charitable functions.

One of the sort of social analogies for them are burial societies.

And you think of the activity around the so-called Christian-Jewish catacombs in Rome, that's one the places that we have frescoes, we have inscriptions, that we can see that these are places where Christians took care of their dead, and so care the dead and belonging is an example of one part of the idea of Christian identity, which is based on the community -- the gathering of Christians together, the practice of charity, calling one another "brother" and "sister."

These kind of family terms show that you are now part of this group, and that is where your primary loyalty is, that is your primary identity, and that you would look after one another in this, in this physical way.

They are providing this care.

They're building a sense of charity, a sense of community, that the Christians are a group apart, but a group that cares, not just for those within its community, but for everyone.

PHILLIPS: The new religion offered both support in the living world and the promise of a better life in the world to come.

The next stop on my journey will be in Asia Minor, modern-day Turkey, a land, as we have seen, where many early Christian preachers spread the word.

In the breathtaking region of Cappadocia, one truly unique set of Christian communities emerged.

Each morning at sunrise, Turkish balloon pilots and their passengers take a sightseeing tour of the area.

Today I'm lucky enough to be one of their guests.

Below me in central Turkey lies a magical, almost surreal, landscape.

Mountainside caves where Christians would live are found all around Cappadocia.

Over time, dozens of rock-hewn churches were created to provide for the religious needs of these growing Christian communities.

Even more astonishing is the existence of over 30 underground cities, designed with escape chutes, rat runs, bottomless shafts, and secret ladders.

While most of these date to later centuries, those that survived can give us a glimpse into the extraordinary life of the people who lived here.

I knew that early Christianity was tough and enduring, but I had no idea that I'd find that a community existed in this staggering collection of underground caves, a place that offered protection to families, animals, harvests, and their faith.

Early Christians have always been here and believing in Christianity in these caves, having their temples here, but not telling everyone.

PHILLIPS: As we go deeper and deeper into this underground city, one of the more remarkable things that I've found is this huge stone wheel.

If the people living here felt threatened, they could roll it across the passage, seal the entrance, and then they could stay here until the danger had passed.

TURGUT: The entrance levels usually become stable for animals, and then right on top of the stable or next to the stable, they have bedrooms, because the animals keep the stable warm.

So with that warmness, they can sleep even in winter in a comfortable temperature in the rooms next to that.

On the upper levels they have some other living rooms that they prefer to stay in summer, in warmer seasons, and they had some tunnels in between these rooms.

Instead of having steps, usually they had some tunnels.

PHILLIPS: For people to live here on a day-to-day basis, a number of basic practical challenges had to be overcome.

I'm three stories down here, but I can actually see daylight, and what we've got here is a ventilation shaft.

I mean, obviously the circulation of fresh air was essential.

And if I just peer over here, I have a pretty death-defying drop of at least another five floors down, so this is a crucial artery in this underground secret world.

MAN: ...As a holiday, and still here, I love here.

PHILLIPS: [ Chuckles ] The early Christians are the same, maybe.

Aisha, like many Cappadocians, still lives much like her ancestors did 2,000 years ago.

Her cave home, despite modern touches, has been occupied for centuries.

My Cappadocian guide, Matthew, took me to meet Aisha at her home.

[ Aisha and Matthew conversing in Turkish ] PHILLIPS: Hello, I'm Jonathan Phillips.

Nice to meet you.

[ Aisha and Matthew conversing in Turkish ] She's saying, "I am happy to meet you."

PHILLIPS: Thank you.

Why did you want to live in a cave?

MATTHEW: [ Translating in Turkish ] AISHA: [ Speaking Turkish ] MATTHEW: She is saying, living here is very healthy, you know, and cool inside.

You don't need, like, air conditioning.

AISHA: [ Speaking Turkish ] MATTHEW: In winter, the inside of the rooms is hot, you know, and in summer is cool.

PHILLIPS: It does feel nice.

I mean, it's quite hot outside now, and it does feel nice and cool in here at the moment.

Does it get damp?

Does it get wet?

MATTHEW: [ Speaking Turkish ] AISHA: [ Speaking Turkish ] MATTHEW: No, never.

PHILLIPS: Aisha showed us her handiwork, beautiful carpets that she weaves and embroiders, each one taking from two to six months to complete.

She sells the finished products at the local market.

To reach her kitchen, you have to go next door to another cave.

Another cave?

AISHA: [ Speaking Turkish ] MATTHEW: She's saying that if you want, I can cook the tea.

PHILLIPS: Tea would be lovely.

Tea would be brilliant.

Thank you.

I can see that this is...

I saw another room in Aisha's cave that is still used as it has been for centuries.

This is just a natural space to...to keep things, Again, as in centuries past, some of the cave cities, they would have stored crops and kept animals and things like that.

At the end of our visit, Aisha invited us to share a cup of tea.

Although our cultures were very different, her hospitality and kindness made me think of the charity that the early Christians showed to one another and to new recruits, a feature that helped attract and bind these people together.

The Christian communities established amongst the people of Cappadocia, as well as those in more familiar cities across the Roman Empire, were really starting to grow.

The expansion of the new religion was slow and uneven.

At the end of the third century, almost 300 years after Christ's death, the Roman Empire was still primarily pagan.

In an empire of around 60 million people, Christians made up perhaps 10% of the overall population.

Most of these early Christians lived in cities rather than in rural areas and were traders and craftsmen.

Many were women.

Christianity also varied widely by region.

In general terms, Christianity spread rapidly in Asia Minor, Syria, Greece, Egypt, and north Africa, and also in Italy, but it spread far more slowly in Gaul, Britain, and Spain -- yet spread it certainly did.

As I continue my journey into early Christian life, I will go to north Africa and tell the story of Perpetua, a young Christian martyr whose extraordinary tale still resonates eighteen centuries after her death.

I will go to Rome and to the very places where Christian belief was tested to its limits, where the Roman Empire threatened everything that Christians stood for with its emperor cult and pagan temples.

The faith was about to enter the greatest persecution to date in the history of Christianity.

I'm Jonathan Phillips.

Join me next time as we continue our journey on the road from Christ to Constantine.