God's Architect: Antoni Gaudí's glorious vision

The following script is from "God's Architect" which aired on March 10, 2013 and was rebroadcast on June 9, 2013. Lara Logan is the correspondent. Max McClellan, producer.

Before stepping down as pope earlier this year, Benedict XVI carried out thousands of official duties over eight years, but only once did he travel outside Rome to bestow the Vatican's highest honor on a church, transforming it into a basilica -- a sacred place forever.

Tonight, we're going to take you to that extraordinary church. It's called the Sagrada Família and, if you've ever been to Barcelona, Spain, you couldn't have missed it. It may be one of the most spectacular buildings ever constructed by man, the vision of genius Spanish architect, Antoni Gaudí, known as God's architect, who died almost a century ago. It's been under construction for 130 years and it's still not finished.

Why would a church take so long to build? Because, as we first reported in March, Gaudí's design was as complicated as it was advanced. Today, the Sagrada Família has become the longest running architectural project on earth.

When Pope Benedict came to the Sagrada Família two years ago, it was the first time mass had ever been held here. In an ancient tradition as old as the Catholic Church, he consecrated the Sagrada Família as a basilica.

Not since 1883, when it was envisioned by Antoni Gaudí, had it been seen in all its glory.

Eight hundred voices filled the air, one of the largest choirs in the world and close to 7,000 people gathered, celebrating a moment that had taken 128 years to arrive.

While the inside is mostly finished, outside there's still much to be done. You can see the spires and construction cranes for miles.

Watch as this picture moves in from above -- those tiny figures below are people dwarfed by the massive facade, rising from the main entrance of the church.

Antoni Gaudí was profoundly devout and this was his way to make amends to God for the sins of the modern world.

Gijs van Hensbergen: I mean, he wanted to write the history of the whole of the Catholic faith in one building. I mean, how crazy and how extraordinary and how ambitious and how, in a sense, megalomaniac that idea is.

Gijs van Hensbergen immersed himself in Antoni Gaudí's life for 10 years and wrote what's considered the definitive biography. He took us to see the Nativity Facade, the only part built while Gaudí was alive.

Gijs van Hensbergen: It's the Bible written in stone.

Lara Logan: So every single little thing that you look at there, every detail symbolizes something real?

Gijs van Hensbergen: Yea, and that was the idea, that we together would spend days here, me teaching you if I was a priest, what the story was and what the symbolism was. And once you get inside is a wonderful, kind of spiritual boost.

The ceiling is a striking display of Gaudí's engineering genius. He wanted the interior of his church to have the feel of a forest because that's where he believed man could feel closest to God. And when you look upwards, you can see Gaudí's columns branching out like trees.

Gijs van Hensbergen: Trees are actually buildings, he said. It knows where to throw out a branch. And if you look at the Sagrada Família today that's exactly what happens with those bizarre, eccentric-- they look bizarre and eccentric but the engineering beneath it is absolutely exceptional.

Van Hensbergen pointed out that, as you move towards the altar, the columns are made from stronger and stronger stone. Gaudí chose red porphyry from Iran, for the ones that bear the heaviest load, because it's among the strongest in the world.

Lara Logan: If you had to define, sort of, the one thing, that distinguished Gaudí as an architect, what would it be?

Gijs van Hensbergen: The capacity to see space in a totally different way, to make space explode, to see a building as a sculpture rather than just as a place to live in or a roof over your head. He's someone who reinvented the language of architecture which no other architect has ever managed to do.

Lara Logan: How many years ahead of his time was he?

Gijs van Hensbergen: Oh he was a century ahead, he was a century ahead.

Gaudí knew the Sagrada Família would not be completed in his lifetime, so he spent years building these elaborate plaster models. This one is of the church's ceiling. They would have to act as a guide for future generations of architects to follow his complicated design and he knew that without them, it would never be finished the way he intended.

[Jordi Bonet: I am very old, but--

Lara Logan: You're very old?

Jordi Bonet: This next month. Yes.

Lara Logan: But?

Jordi Bonet t: 87.]

Gaudí's legacy has been in the hands of this man's family for more than 80 years. Jordi Bonet came here for the first time in 1932, when he was just 7 years old.

Lara Logan: Do you remember what this was like when you first came here?

Jordi Bonet: Yes.

Lara Logan: Was it nothing like this?

Jordi Bonet: Nothing of this - only this facade, the walls. And the other facade. This was nothing.

For years, the Sagrada Família was little more than a ruin, a pile of rubble and open sky. And it may have stayed that way were it not for this one family.

This is Jordi Bonet's father who was one of the lead architects here for more than 40 years. Jordi followed him as chief architect for almost three decades. And his daughter Mariona is an architect here today. Together, they've spent more time working on this church than Gaudí himself.

The devotion to Gaudí runs deep here. Japanese sculptor Etsuro Sotoo has spent 35 years in this church and this is where he expects to be for the rest of his life, sculpting the figures that adorn Gaudí's final masterpiece, consumed by the man and his vision.

Etsuro Sotoo (translator): Gaudí teaches me and helps me solve problems in my work. For me, he's not dead.

Lara Logan: Why did you convert to Catholicism? You became a Catholic.

Etsuro Sotoo (translator): I was a Buddhist. But after working here, I realized I couldn't do my job without knowing Gaudí, and to know him you have to be in the place he was, and that was a world of faith.

Gaudí's deep faith is the reason he became known as God's architect. This is one of the few photographs ever taken of him. He was 31 when he started working on the Sagrada Família. And over the next 43 years, it became an obsession.

Gijs van Hensbergen: He looked like a homeless person. His trousers were held up with string. His clothes were kind of frayed, and-- Because all he was interested in was the Sagrada Família. I mean that was every waking hour. To the point at the end of his life, actually, where he was sleeping on the site.

Gaudí died suddenly at this intersection, in 1926, when he was hit by a tram. The driver pushed him aside, mistaking the beloved architect for a tramp.

Gijs van Hensbergen: The photos show you these people kind of bereft of their builder. The builder of God.

After his death, the builder of God's plaster models continued to guide construction for the next 10 years, until 1936, when the Spanish Civil War broke out.

Anarchists attacked the Sagrada Família. This photo captures smoke billowing from its sides. All those models Gaudí had spent years building were smashed to pieces.

Lara Logan: Wow, these are all the original pieces that were picked up from his studio?

Mark Burry: Yup, and they've been sort of painstakingly identified.

These shattered fragments were rescued from the rubble and ashes by Jordi Bonet's father and a team of architects. There are thousands of them locked away inside this room in the Sagrada Família. They are the structural DNA of Gaudí's church.

Mark Burry: They are absolutely the link. Not a vague link, not a, a source of evidence, it's the source of evidence.

New Zealander Mark Burry was studying architecture at Cambridge University in England when he first came to the Sagrada Família on a backpacking trip in 1977.

He'd come at just the right moment. The architects were stuck. The second facade had just been completed and they were ready to take on the main body of the church, but no one could figure out how to build it as Gaudí intended.

Lara Logan: What were you going to do that they couldn't do?

Mark Burry: My task was to actually reverse engineer the models, if you like.

Reverse engineer them so he could understand how Gaudí's models were supposed to fit together, almost like the pieces of a complex puzzle. He told us Gaudí's design was so advanced there was nothing like it in the language of architecture at the time. In the end, he turned to the most sophisticated aeronautical design software available.

Mark Burry: We had to look to other professions who've actually tackled the complexities of the Sagrada Família, which are basically complex shapes and surfaces so that's the vehicle industry: the car designers, the ship designers, the plane designers. They've been grappling for decades with the very same issues that Gaudí was putting up as architectural challenges.

Lara Logan: So you are using the most up to date aeronautical engineering software to complete something that he conceived of in the late 1800's.

Mark Burry: Absolutely.

After 34 years, Mark Burry is now one of the lead architects. He took us up to their construction site in the sky, way above the city. From up here, you can see all the way to the Mediterranean.

Lara Logan: How did they build these towers a 130 years ago?

Mark Burry: They built them by hand.

Today, massive cranes swing heavy equipment and materials across the sky, constructing the Sagrada Família precisely as Gaudí envisioned. Burry says they still rely on Gaudí's models to guide them, nearly a hundred years later.

Mark Burry: What's extraordinary is because of the system that Gaudí put in place using these particular geometries. It all fits within fractions of an inch.

The spot where we're standing is where they're building Gaudí's central tower. At 566 feet, it will make this the tallest church on earth. Gaudí designed it to be three feet shorter than the tallest surrounding mountain in deference to God.

Lara Logan: When you finish this tower it's going to be double where we are right now?

Mark Burry: We're going to get this view amplified by two.

Mark Burry says it will take at least another 13 years to finish the Sagrada Família, which is paid for entirely by donations to the church.

During the pope's visit, Jordi Bonet was called on to represent the three generations of architects, engineers and sculptors who have brought Gaudí's vision this far.

Lara Logan: Do you think you will see this complete?

Jordi Bonet: This is very difficult to answer. My age is a big age. But it is possible.

Lara Logan: Do you have any doubt in your mind that this will be finished one day?

Jordi Bonet: Oh yes, I believe.