If faith is a mystery, there are few places in the Christian world where the mystery is deeper than in Lalibela. 800 years ago, an Ethiopian king ordered a new capital for Christians. At 8,000 feet, on the central plateau of Ethiopia, stand 11 churches, each carved from a single, gigantic, block of stone. No bricks, no mortar, no concrete, no lumber, just rock sculpted into architecture. As we recently reported, not much is known about who built them, or why. But the faithful of the Ethiopian orthodox church say there's no mystery really, the churches of Lalibela were built by angels.

The northern highlands of Ethiopia rose 31 million years ago when fissures in the earth flooded the Horn of Africa with lava a mile deep. On hillsides you can still see columns of lava frozen in time. Iron made the basalt red and, gases trapped inside, made the stone light, as light and pliable as air. Christians laid their mark on Ethiopia before the year 400. They found the ancient stone welcomed the bite of a chisel. The churches were carved around the year 1200 by people called the Zagwe.



Their king, Lalibela, is said to have traveled the 1,600 miles to Jerusalem. Legend has it, when he returned and Jerusalem fell to the Islamic conquest, Lalibela ordered a new home for Christianity.



Fasil Giorghis: And he came back with an ambitious idea, a vision of creating an African Jerusalem, a black Jerusalem here in the highlands of Ethiopia.



Fasil Giorghis is an Ethiopian architect and historian who walked us through the rock of ages.



Fasil Giorghis: Well, there are three groups of churches, and each group is interconnected within itself.

Scott Pelley: We're sitting in Saint Mary's Church. How was it built?

Fasil Giorghis: Well, it was built starting from outside. They formed the shape. And then they start digging or excavating downwards.

Scott Pelley: So they dug, essentially, a trench around the whole perimeter which left them with a giant cube of solid rock.

Fasil Giorghis: Yes. Exactly.

Scott Pelley: And then they carved their doors and in they went?

Fasil Giorghis: In they went.

Pilgrims near a church at Lalibela

Chipping inside, largely in darkness, artists sculpted many rooms with no room for error. Archways, vaults and columns imitate traditional construction even though, in solid rock, there's no need to hold up the ceiling. The enduring mystery is why. Why did king lalibela attempt the seemingly impossible when easier building techniques were known?



Scott Pelley: As the story goes, he was helped by angels.



Fasil Giorghis: Yes.



Scott Pelley: Who worked on the project overnight.



Fasil Giorghis: I think I would rather take this as a symbolic thing because--



Scott Pelley: Do you not have any experience working with angels in architecture?



Fasil Giorghis: Well, I get inspiration from angels.



The site of the 11 churches covers about 62 acres. It's divided by a stream King Lalibela christened, the river Jordan. The largest church covers around 8,000 square feet, each is about four stories tall. But their most astounding dimension cannot be measured. It is the length to which they summon adoration.



Fasil Giorghis: This is considered to be a holy place, that coming here as a devout Christian is a very strong sign of their belief. Some people travel hundreds of kilometers to get here on foot. On foot. And they have been doing it for several centuries.

The churches are open for worship year-round but we were there Christmas Eve when nearly 200,000 pilgrims rose to heaven on a path descending into the earth. Many walked for days or weeks, fasting, robed in white—an ordeal that is rinsed from the disciples in the tradition of Jesus. Any Ethiopian, over the age of 30, cannot forget the suffering of drought and war and a million people lost to starvation. And so, having known poverty in this life, they've invested their souls in the next.



Tewede Yigzaw, told us, "I believe God is here. I came with faith." Her neighbor, Getaye Abebeaw and his daughter told us they walked from their farms nearly 100 miles away, a journey of three days.



Scott Pelley: God can hear your prayers anywhere. Why did you feel you had to be here?



Tewede Yigzaw (Translation): "So that God can see our devotion," she said, "and our dedication."



Getaye Abebeaw (Translation): "We were very tired," he said, "we were falling and getting back up throughout the journey, all to see the celebration here. And God will recognize our effort."



The Christmas celebration Ethiopians call Genna compresses them, shoulder to shoulder, to fast and chant and praise all night 'til dawn brings Christmas Day. The Ethiopian Orthodox Church claims to be among the earliest capitals of Christianity thanks to a mysterious figure of the Hebrew Bible.



The faithful believe that the Queen of Sheba left Ethiopia, went to Jerusalem where she met King Solomon. From that meeting came a son, and, when the son was an adult, he returned to Ethiopia with 12,000 Israelites and the Ark of the Covenant, containing the tablets with the word of God, the 10 Commandments.

And the Ark remains in Ethiopia, according to the priests of the orthodox church. We met Tsigie Selassie Mezgebu, the head priest of Lalibela at the church of St. George, which was last to be built and judged to be the masterpiece.

Scott Pelley: I met a woman on Christmas day who had spent three days walking here. Who are these pilgrims?

Tsigie Selassie Mezgebu (Translation): "These are believers," he told us, "Not just three days, even three months sometimes. When there was no air travel or buses, people used to travel from various parts of the country for months, to come here and celebrate with us."

Pilgrims on their way to Lalibela

The celebration beats to the rhythm of ancient instruments; the kebero double-headed drum and a rattle called the sistrum, whose sound was known in North Africa 3,000 years before Jesus.

Scott Pelley: On Christmas Eve, we watched you and your priests lead the chant all night long. What are you saying in that chant?

Tsigie Selassie Mezgebu (Translation): "We tell the people that God became human and a human became God. Because of Christ, we went from being punished by God to being his children again. Christmas is the day that forgiveness was born."

But, while God forgives, time does not. After eight centuries, the Basalt Basilicas are weary of wind and water.

Stephen Battle: What's absolutely clear is that something quite miraculous happened here.

Stephen Battle is an architect with the World Monuments Fund who told us Lalibela's miracle is being undermined because the rock is not rock solid.

Stephen Battle: When you're building a conventional building, you go to a quarry, and you'll have different grades of stone. And you try and select the best stone. You leave the bad stuff behind. When you're carving a church out of the mountainside, you don't have that luxury. And so, typically, in any one of the churches here, you get good stone. And a lot of it is good stone. But then you also get actually bad stone and actually very bad stone, which is really very soft indeed. And over time, if you touch it, it actually crumbles.

Simon Warrack: And this is one of the most sacred parts of Lalibela.

We saw the good and the bad in the chamber where King Lalibela is laid to rest.

Scott Pelley: This is one of the best-preserved sculptures I've seen at Lalibela.

Simon Warrack: Yes. This is particularly beautiful. And they're also painted.

Simon Warrack is a master stone mason also with the World Monuments Fund, a U.S.-based charity that preserves some of humankind's great achievements.

Warrack has repaired European cathedrals and Roman antiquities. But Lalibela is more complicated because of the sincere belief that angels worked this stone.

Scott Pelley: Simon, you can't actually cut this stone in order to fit a new piece in, because the stone you would be cutting is sacred.

Simon Warrack: Yeah, this was one of the first big issues that I came across. If we ever had to drill a hole to strengthen it to put in a pin, we had to discuss it with the priests. They collected the dust. There was a whole procedure around touching the fabric of the church.

Scott Pelley: The priests collected the dust?

Simon Warrack: Yes, yes.

That was the issue when Warrack was asked to resurrect the cross in a window without disturbing the fragment that remained.

Scott Pelley: So this cross wasn't here.

Simon Warrack: This was completely gone, yes. It was a very thin piece of stone remaining.

Simon Warrack: So I hollowed out the back of the cross shape that we were inserting, so that it was fitting over the original stone, a bit like a dentist. And so we were able to conserve this tiny bit of stone, which is, in stone masonry terms, it's crazy. But you have to do that in this kind of situation.

There have been other crazy conservation ideas. A dozen years ago, five umbrellas were built to keep the heavens from pouring down.

Stephen Battle: The local people call them gas station roofs. And I think it's a pretty apt way of describing them. So you can imagine, we have this extraordinary site with some of the most beautiful buildings in the world with extraordinary, huge, spiritual significance. And there's a bunch of gas station roofs that have been placed over the top of them. It's really not compatible, it's not appropriate.

Unholy to behold, the roofs became a lesson in the law of unintended consequences. The churches were too wet, now they're too dry.

Scott Pelley: For the first time in 900 years, they're not being rained on.

Stephen Battle: Exactly right. And so the stone is contracting much more than it has ever done before. And what happens is this creates little failures on a micro level and the stone starts to crumble.

The roofs were meant to be temporary and in a few years they must be recovered. Stephen Battle prays they'll be removed altogether and replaced by intensive maintenance. To that end, the World Monuments Fund is teaching conservation to dozens of Lalibela's priests and laymen in the hope that a host can protect the heavenly perhaps for centuries to come.

Scott Pelley: How long can they last?

Stephen Battle: Well another 900 years, if they're looked after properly. Oh yes, way beyond a shadow of a doubt, absolutely, if they're looked after correctly.

Even beyond another millennia, we're not likely to know with certainty the answer to why. Why attempt what must have seemed impossible? No answer was apparent until we chipped away at what we saw Christmas Day. In the Old Testament, Isaiah advises those who seek God to, "look to the rock from which you were cut and the quarry from which you were hewn." Whoever cut this rock, angels or man, understood that, in the presence of a miracle, faith is never washed away.

Produced by Nicole Young. Associate producer, Katie Kerbstat. Broadcast associate, Ian Flickinger.