Ghosts of Machu Picchu

PBS Airdate: February 2, 2010

NARRATOR: High in the Peruvian Andes, there's an ancient city called Machu Picchu. It is a ruin that defies explanation. Who were the mysterious people who built it and why did they build it here?

With no defensive wall, it doesn't look like a fortress. Instead, there are fountains and small pools, temples and strange altars cut from granite, but little else to explain how a people who didn't have iron tools or the wheel could have created such a masterpiece and why.

Now, new research is solving these mysteries in the bodies and bones of the people who once lived here.

VALERIE ANDRUSHKO (Southern Connecticut State University): To me, this is the type of injury more indicative of a weapon, possibly of warfare.

NARRATOR: There are clues far below the city and underneath it and in the stories of the mummies of kings. Will all these revelations finally lay the Ghosts of Machu Picchu to rest? Right now, on this Nova/ National Geographic special.

Perched at 8,000 feet on a narrow ridge in the high Andes, Machu Picchu is a remote and mysterious ancient wonder.

Spread across the top of this ridge are more than 200 structures, each built with exquisitely cut stone. Some appear to be homes, others temples. They surround a one-acre green, and all are fed by open waterways and fountains.

It is a lost city, whose doorways and passages hint at the ghosts of its past; a place that is at once beautiful and baffling.

There are no written clues in the city, no carvings to suggest a purpose.

At its highest point, the mystery only deepens.

There, a beautifully carved pillar stands, a graceful riddle to cap the site. From this lofty height, the views leave one stunned, but also curious. How did the builders get all this stone up here and then cut it so finely that they didn't even need mortar to hold their walls in place? Who built Machu Picchu? And why did they build it in this impossible place?

Even more perplexing, why did they abandon it? Throughout the city, stones seemed to be on the verge of being placed when work came to a stop.

Now, as never before, clues are emerging—some at the site itself in new excavations, others at the lower reaches of Machu Picchu—as teams explore them for the very first time.

These mysteries have long obsessed Fernando Astete, director of the Machu Picchu Archaeological Park.

FERNANDO ASTETE (Machu Picchu Archeological Park/Translation): There is such an important cultural legacy here, not just for Peruvians, but a legacy for the entire world.

NARRATOR: Making sense of that legacy is Astete's challenge—along with getting to work. He has one of the most precarious commutes of anyone on the planet. His path was built by a people who were sure-footed, with little fear of heights, the Inca.

They rose to power in the mid-1400s in part because they built such good roads. Much of their 10,000-mile network is still visible today.

They left other evidence that they were master engineers and builders. Their terraces, canals and stone cities rival those of ancient Rome. But unlike the ancient Romans, they did all of this without the wheel, without iron and without a written language.

The Inca did have a calculating system, using knotted strings called khipu, but it left no record of their lives or their history. So, much of what we do know comes from the Spanish who conquered them in the 1500s. These accounts carry the bias of conquerors.

A different view comes from an Inca artist named Guaman Poma. Poma was born shortly after the Spanish arrived in Peru, so he was an observer who bridged both worlds. He produced hundreds of simple drawings about farming techniques, royalty and the Inca history of conquest.

From both these sources, we know the Inca were fierce warriors who subjugated dozens of different peoples, forging them into one of the largest empires in the world, stretching some 2,400 miles.

They fed their people by transforming steep slopes into farmland with the rise and run of terracing. It's believed that more land was under cultivation during Inca times than is today in modern Peru.

But the most surprising detail about the Inca is that they ruled for only 100 years. Then, their empire was decimated, first by disease, then civil war, finally the Spanish Conquistadors.

From the Spanish, we know that the last Inca emperor retreated into the mountains, to a city called Vilcabamba. The Inca held out at Vilcabamba for 35 years, until, finally, in 1572, the Spanish destroyed the city.

Strangely, they left no written record of where it was located, and the legend of the lost city of Vilcabamba was born.

It was a mystery that had powerful allure.

Almost 350 years later, it pulled an American explorer named Hiram Bingham here on a quest to find it. On the morning of July 24, 1911, Bingham, camera at the ready, reached the top of a ridge and stepped into history.

"It fairly took my breath away," he later wrote.

Bingham's photos marked one of the first times that a moment of discovery had been captured on film. Today, those pictures are part of a rare 23-volume explorer's album detailing Bingham's discovery. But what, exactly, had he found?

He called it by its local name, Machu Picchu, but he thought it was the lost city of Vilcabamba. A year later, when his team discovered over 100 burials, Bingham believed he'd found the evidence to make his case.

After thorough examination, Bingham and his bone expert, Dr. George Eaton, reached an astonishing conclusion: 80 percent of the dead were women.

JOHN VERANO (Tulane University): Eaton's data gave a sex ratio of four to one, four times as many females as males. Four to one really would be a tremendous bias, and I think that's what got Eaton excited. He thought, "My god, they're almost all women."

NARRATOR: What could explain a predominantly female cemetery?

Bingham thought he'd found the remains of the so-called "Virgins of the Sun." According to Spanish accounts, the most beautiful girls in the empire were chosen for this sacred convent. Selected around the age of eight, these virgins served the Inca emperor for the rest of their lives.

Bingham guessed that when the last Inca king retreated into the mountains to escape the Spanish, he took his sacred virgins with him, so it all added up. The skeletons of the virgins confirmed that this spectacular city in the sky had to be Vilcabamba.

JOHN VERANO: Clearly, for him, it created a great magical, romantic kind of picture that, that made good book-reading.

NARRATOR: When published in the April, 1913, issue of National Geographic , the story was an overnight sensation. Bingham became a star.

The only problem was that the theory was wrong. Investigations of other Inca ruins revealed that the Spanish desecrated almost every Inca holy site they could find; at Machu Picchu, the entire city remained untouched.

But the most convincing evidence against Bingham's theory was in the very bones he had found at the site. When forensic anthropologist, John Verano, reexamined them, he found that the sex of the skeletons was almost evenly split, a far cry from Eaton's four to one ratio.

To figure out the sex of a skeleton, you have to compare it across many ethnic and racial groups. Eaton's references were limited to people of European or African descent.

JOHN VERANO: People in the Andes are, are relatively short, delicately built. And I can only guess that what he was looking at was bone size, and he said, "This looks like a small person, therefore it's female."

NARRATOR: In Bingham's collection, Verano also found the bones of several children. And children and virgins just didn't add up.

JOHN VERANO: I just, I can't find evidence to support that idea that these were Virgins of the Sun. I think that that can be pretty well ruled out.

NARRATOR: Without the virgins or any sign of Spanish desecration, there was no proof to support Bingham's theory that this was Vilcabamba.

So what was it?

With so few written records, archeologists, like Fernando Astete, must piece together clues about Machu Picchu's history wherever they can find them. And he thinks he's just found one in a nearby town called Patallacta.

FERNANDO ASTETE (Translation): Patallacta was important because it supplied the food for all the people living at Machu Picchu.

NARRATOR: Patallacta is a few hours walk from Machu Picchu, along the main Inca trail through the region. It is the closest place to Machu Picchu where large-scale farming could have taken place.

FERNANDO ASTETE (Translation): The people who lived at Patallacta weren't just farmers though, they likely played many roles. They could have been stoneworkers, builders, laborers.

NARRATOR: Astete's best hope for understanding Machu Picchu is to learn about the people who lived here, the possible builders of the city.

Above the old Inca town, up a nearly vertical slope, a local guide has found what looks like a burial niche. Astete and fellow archaeologist, Elva Torres, believe it may be undisturbed, a gravesite last touched 500 years ago.

Before the tomb can be opened, Astete's Quechua guide makes an offering of coca leaves to the spirits that dwell here, just as his Inca forbearers would have done.

Astete and Torres have investigated many other burials in the area. Most are far more accessible.

ELVA TORRES PINO (Peruvian Culture Institute/Translation): This tomb has been constructed.

The other tombs don't use this style. They're simply in caves, in natural rock formations that are easy to get to.

NARRATOR: In the dim tomb light...a human skull.

As Torres enters the cramped tomb, the find only gets more tantalizing.

ELVA TORRES PINO (Translation): It appears there's a couple of individuals.

NARRATOR: But as she investigates, she finds a lot more skeletons—nine in all—and many show signs of injury.

ELVA TORRES PINO (Translation): Well, this problem regarding fractures, they could be from everyday activities. They could have been from a fall, something may have fallen on them, or perhaps some other sort of activity.

In this case, they may have been working in the quarries.

NARRATOR: Could these be the skeletons of the builders of Machu Picchu? They can't be sure until they take a closer look in the lab.

There, Torres is joined by bio-archeologist Valerie Andrushko.

Right away, they find some surprises in the skulls from Patallacta. They're full of holes. It's the sign of a procedure called trepanation.

VALERIE ANDRUSHKO: Trepanation is the partial removal of part of the skull, that the Inca practiced with very high degrees of success.

Our understanding is that trepanation was often done in order to release intracranial pressure due to fractures.

NARRATOR: It's skull surgery, and healed wounds found throughout the empire show that the Inca were skilled at using it to treat head trauma.

VALERIE ANDRUSHKO: When we see evidence for trauma, the question is always, is it related to accidents or is related to violence?

This individual right here, this is a complete fracture of the frontal bone. It has perforated all the way to the frontal sinus.

This type of injury is not the type of injury that one would get from an accidental fall. To me, this is the type of injury more indicative of a weapon type injury, possibly indicative of warfare.

NARRATOR: In fact, several skulls from the tombs show signs of blunt force trauma, the type of fracture you'd get from a club. So these weren't builders; they were, likely, warriors.

Possibly, these individuals may have been engaged in defense of the sites around them, possibly engaged in the defense of Machu Picchu.

This revelation stands in stark contrast to the appearance of Machu Picchu as a religious sanctuary.

This is a city dominated by sacred temples and shrines: the Temple of the Three Windows; the Temple of the Condor, named for its carved floor and stone wings; the elegantly curved Temple of the Sun, built on a rock that is illuminated on the solstice; and, at the highest point in the city, a stone pillar known as the Intihuatana.

The evidence seems to be in conflict: was Machu Picchu a military fortress or was it a religious center?

The answer can perhaps be found in the ancient capital of Cusco, where the descendants of the Inca still live.

Every year, during the Roman Catholic festival of Corpus Christi, statues of the Virgin Mary, along with 15 other saints, are removed from the cathedral and brought to the square.

These performers may be paying homage to Christian saints, but the instruments they play and the steps they move to are actually Inca in origin. That's because this Corpus Christi procession is a Christian revision of an Inca ritual.

Five hundred years ago, the Inca also processed through Cusco, but they didn't carry statues of saints. They carried the mummies of their kings, whom they revered as gods.

It was likely one of these kings who built Machu Picchu. The quality of the stonework alone suggests the city was royal. Fernando Astete estimates that it would have taken at least 50 years to complete. Since the Inca Empire only lasted 100 years, focus has been on the earliest kings.

The accounts of a Spanish Jesuit named Bernabé Cobo point to a dynamic leader who founded the Inca Empire, a king named Pachacuti. But no one could ever prove that Pachacuti built Machu Picchu.

A small clue was hidden in his name, which means, "He who remakes the world."

JOHAN REINHARD (National Geographic Explorer-in-Residence): Pachacuti was sort of the Alexander the Great of the Incas. He was the one who started the expansion out of the Cusco region, and the Inca Empire began to expand tremendously over areas that had never been conquered by the Incas before.

NARRATOR: What we know of Pachacuti's history is due in part to Father Cobo.

Cobo arrived in Peru after the conquest in the late 1500s and wrote his account based on interviews with descendants of the Inca.

According to Father Cobo, Pachacuti was renowned as a builder.

FATHER BERNABí COBO (Written in Chronicles , Dramatization): Having enlarged his empire with so many and such vast provinces, during the remainder of his life this king devoted himself to building magnificent temples and palaces and strong castles.

NARRATOR: The beautiful stonework at Machu Picchu, so similar in style to Pachacuti's temples in other Inca cities, suggests that the same hand was behind the structures here. But the most convincing evidence linking Pachacuti to Machu Picchu comes from a Spanish register, held in the colonial archives in Cusco. Dated 1568, it mentions the town of Picchu with a clear reference to its owner, Inca Yupanqui, also known as Pachacuti.

The evidence is convincing. It is Pachacuti, the first Inca emperor, who ordered Machu Picchu's construction, and in a place that would give any engineer pause.

KENNETH WRIGHT (Paleohydrologist): If I was called in by Pachacuti and ordered to build Machu Picchu at that particular location, I would have gulped. Engineering-wise, it would seem almost impossible to handle.

NARRATOR: Fifteen years of study by hydrologist Ken Wright and a team of engineers is revealing how the Inca pulled this off, because the steepness of the site isn't the only problem.

Machu Picchu also receives torrential rains each year, triggering frequent landslides. And the site is crossed by not one, but two earthquake fault lines, making it a terrible place on which to build a city of stone.

The location does have two virtues: a nearby fresh water spring and a supply of granite; there's a quarry right on the site.

When the Inca engineers turned to building, their first step would have been to shore up the mountain.

They did it by constructing a remarkable bulwark of terraces.

As Astete's team rappels further down the cliff face, they are discovering hundreds of new terraces hidden below.

FERNANDO ASTETE (Translation): Usually, when people refer to Machu Picchu, they're only thinking about the Inca buildings on top of the ridge, but construction has to begin at the bottom. In other words, you have to start with the terraces.

NARRATOR: Terraces are fundamental to Machu Picchu.

While some terraces would have been used for small-scale farming, their primary purpose was to hold the mountain in place while draining a huge volume of rainwater away.

KEN WRIGHT: That averages about 76 inches per year, and, in terms of let's say middle America, that's a lot of water: roughly two and half times as much as the city of Chicago would get.

NARRATOR: Left unmanaged, that rainwater would turn the hillsides to mud, and Machu Picchu would slide away.

The Inca avoided that by creating a sophisticated drainage system. Inside the terraces, archaeologists found a layer of rich topsoil, under that, a layer of sandy dirt, and finally, gravel and larger stones.

FERNANDO ASTETE (Translation): We could say that they are filtering galleries, meaning, even when you get a lot of rain, the terraces never flood, because the water is filtered through these progressive layers of material.

NARRATOR: Instead of racing down the mountain, the water slowly works its way into the ground so there's almost no erosion.

With this basic design in hand, the Inca fixed the first terrace into the mountain, then started on the next, replicating their way to the top.

Once there, Inca engineers had to reckon with an even bigger water problem.

This is a city paved with stone with few places for rainwater to go. But the Inca had foreseen that problem, and, during construction, carefully placed more than a hundred drains throughout the city.

Many of these drains delivered the runoff from the elevated parts of the city into the central plaza. Further digging there revealed a remarkable innovation to handle all of that water. Beneath the usual layers of topsoil and gravelly dirt, Wright's team hit a thick layer of white granite chips, the spoil from years of Inca stone cutting.

KEN WRIGHT: In effect, what the Inca did was to build an underground drainage system, a type of conduit, to carry water safely away.

NARRATOR: These were colossal earthworks, extending nearly nine feet below the surface and encompassing several acres. They collected water and shunted it away from the city.

KEN WRIGHT: The Inca engineers spent about 50 percent, maybe 60 percent of their overall effort underground, doing foundations, site preparation, to make sure that Machu Picchu would last forever.

NARRATOR: So as vast as the city appears, there's 60 percent more of it underground, holding it all in place.

While the Inca went to great lengths to get rid of water, they also built fountains which seem to celebrate it. There are 16 fountains in the city, each beautifully designed and a practical source of drinking water.

The fountains are fed by a natural spring, found nearby on the flanks of Machu Picchu Mountain. From there, the Inca engineered a canal whose three percent grade was carefully crafted to deliver just the right amount of water to the fountains.

Wright calculated the flow to be between 6 and 30 gallons per minute, depending on the time of year; enough to sustain a population of close to a thousand people.

KEN WRIGHT: It was remarkable. It was something that created great respect by us, for the Inca engineers, all those years ago.

NARRATOR: It is a respect also shared by Astete's team as they restore the Inca's original stonework.

In spite of their lack of iron tools, the Inca were somehow able to transform granite, a notoriously hard stone. There's a clue to how they did this in Machu Picchu's quarry.

FERNANDO ASTETE (Translation): We see here the basic method the Inca used to cut rocks.

The idea is to create a neck in the block and then cause it to fracture.

NARRATOR: It was bone-jarring work.

FERNANDO ASTETE (Translation): The technique the Inca used was direct hammering.

With the rough blocks, they'd start with a large tool, like this one. As you can see, it sheers very easily.

Then they'd gradually use the smaller and harder tools to give it that strong, smooth surface.

NARRATOR: Once the cutters had roughed it out, they put the stone on log rollers or mud and pulled it close to the construction site. The final step was to move the stone into place, and match it to its mate.

FERNANDO ASTETE (Translation): And here is the indentation they made, which matches the edge of the rock below it.

It's held up by this wedge, until they shape the two surfaces to match. Then the wedge is removed and the two stones fit together perfectly.

Here you can see the brace points they used to push the block up into place. They put beams here to lift the rock up. Once the rock was in place, these points were beaten, just as you see here, and here, in all these other rocks.

That means that the finishing work was done at the site. We can see that this corner wasn't finished yet; all this portion was yet to be cut off in order to finish the wall.

NARRATOR: Driven by a royal mandate to build it here, Machu Picchu is a tribute to Inca engineering and artistry. Its hundreds of terraces buttress it from below. The granite walls are still solid, after 500 years, because of a remarkable drainage system. And it is crowned by an ingenious lacework of fountains cascading from the mountain spring above.

But why go to all this effort? Why did Pachacuti order Machu Picchu built in this forbidding place? Was it for religious reasons?

What we know of Inca religion comes again from the chronicles of Father Bernabé Cobo, written after the Spanish conquest.

FATHER BERNABí COBO (Written in Chronicles , Dramatization): They worship with equal reverence and with the same ceremonial services, the sun, water, earth and many other things that they held to be divine.

NARRATOR: The Inca believed that the sun and the mountains were deities that had to be appeased through ritual. Cobo reported that one of these rituals was child sacrifice.

This claim was dramatically confirmed, in 1999, by high-altitude archaeologist, Johan Reinhard. Then, Reinhard discovered three perfectly preserved child mummies on a high peak in Argentina, in the southern part of the Inca Empire. They had been sacrificed as an offering to the same mountain gods Cobo described.

Perhaps the mystery of Machu Picchu's location can be explained by this reverence for the landscape.

JOHAN REINHARD: We know that throughout the Andes...that people believed that the natural environment has sacred aspects to it. These landscape features at Machu Picchu have helped explain what, otherwise, is a tremendous mystery.

NARRATOR: This idea, called the "sacred landscape" theory, suggests that, in addition to worshipping the sun, rivers and mountains as gods, the Inca derived power by being physically connected to them.

So, is that why Machu Picchu was here?

Machu Picchu is an unusual place to build even for the Inca. Their capital, now modern-day Cusco, and other Inca towns like Pisac, are in flatter, more accessible terrain.

It's also remote: a five-day walk from the capital in Inca times; and today, it takes tourists four hours by train, followed by a harrowing bus ride up to the ruins.

But throughout the site are hints why the Inca thought that this place was worth the trouble.

In certain places, the Inca carved stones in the shape of sacred peaks surrounding the city, then displayed them like massive, holy icons.

Even Bingham was struck by stones like this one, called the Sacred Rock, that mirrors the outline of Mount Yanantin, directly to the northeast.

In Inca times, visitors would approach Machu Picchu from above where they could see the city is surrounded by the holy Urubamba River. For an agricultural people, there was nothing more important than water, and here was a place firmly in the water's embrace.

There is one more piece of evidence connecting Machu Picchu to the sacred landscape. At the top of a pyramid-shaped peak, within the complex, is the sacred pillar known as the Intihuatana. This sacred pillar is in alignment with four mountain gods of supreme importance to the Inca, according to Johann Reinhard.

JOHAN REINHARD: The Intihuatana is situated such that it's at a high point in the center of the entire complex.

But at the same time, it's the center of this massive landscape, because you have, in the far distance, these great snowcapped peaks—the highest ones in the entire region.

NARRATOR: They also happen to correspond to the cardinal directions.

Its views to sacred peaks, proximity to the holy river, and the alignment with four powerful mountain gods must have made this location irresistible to the Inca.

But how did the first Inca emperor, Pachacuti, actually use Machu Picchu? Within the city, there was a distinctive royal residence. It is located near the first fountain, insuring that the king would have the purest water to drink. It's also close to the holiest temples.

But whether the city was Pachacuti's royal court, a religious center or a military post remains a mystery.

A re-analysis of the skeletons that Hiram Bingham found suggests a possible solution.

During Bingham's excavation, in 1912, his team mistakenly identified these skeletons as the Virgins of the Sun. Recently, they've been reexamined. If we could identify who these people were, it might explain how Machu Picchu was used.

During his study, anthropologist John Verano found no evidence of violent injury, so these weren't soldiers. He also confirmed that their burials had been simple, with no high value artifacts. That meant they weren't royalty. In their bones, Verano found hints that they weren't common laborers either. Instead, they were from a class of people in between.

JOHN VERANO: I didn't see a lot of arthritis, even in the older adults at Machu Picchu, and that, again, made me think these are not people working really hard in the...with, say, stone masonry or dragging rocks up the hills.

NARRATOR: A critical clue to their identity can be found in their diet, through a technique called isotopic analysis.

In this process scientists vaporize a small sample of bone. They are looking for the chemical traces of the foods that have been absorbed into its structure. Among the vaporized particles, they found a high percentage of carbon-13 isotopes, which is the signature of corn.

Though it's common in Peru today, in Inca times, corn was a royal food. In fact, pollen analysis of the soils from the hundreds of terraces here shows that the little food grown at the site was primarily corn.

And, as John Verano found, corn leaves another signature.

JOHN VERANO: Corn is rich in carbohydrates. It's not good for your teeth. So they had a lot of cavities, they had a lot of abscesses, a lot of tooth loss.

NARRATOR: So, although they weren't royals, these people frequently helped themselves to the royal corn. They also didn't do a lot of heavy labor, so what were they doing here?

JOHN VERANO: In some ways, I guess you could see it as a big hotel staff: the caretakers and servants of the estate.

NARRATOR: This was a large staff. Verano ultimately identified the remains of 177 individuals.

The evidence is strong that Machu Picchu was a royal estate for the emperor, Pachacuti.

This would have been a peaceful retreat where he and his courtiers would have come to rest, worship and enjoy themselves, their needs tended to by well-trained royal servants.

JOHN VERANO: And you can kind of imagine an entourage of the royalty coming from Cusco, along the road, and everybody at Machu Picchu saying, "Whoops, let's get it ready, clean it up, and get food and so on and welcome our guests."

NARRATOR: But the new finds from the tombs at the nearby farming center of Patallacta don't seem to fit with this peaceful picture. The severe injuries in those skeletons suggest that Machu Picchu may have been connected to warfare. So how could Machu Picchu be a place of both war and peace?

According to Spanish accounts, the Inca conquered this valley about a decade after Pachacuti came to power. So perhaps he built it as a way to seal his conquest.

STELLA NAIR (University of California, Riverside): Incas were very skilled in psychological warfare, and they decide to build this magnificent estate on the hilltop that everybody living up and down that valley is going to see, from the first thing they walk outside their door to the last thing that they go to bed at night.

That's a very powerful thing.

It's a message of conquest and of possession, that they own that land and they control the people who live within it.

NARRATOR: So Machu Picchu was a formidable symbol of Inca power, a spectacular boast by Pachacuti, not just of their engineering prowess, but of their paramount link to the sacred mountains and rivers.

Still, if this place played such a critical role in demonstrating the religious and military power of the Inca, why didn't the Spanish deface it as they did to other sacred Inca sites? And why isn't it ever described in any Spanish accounts?

Part of the answer lies in the Corpus Christi procession back in Cusco, the annual festival that is a Christian revision of an Inca ritual. In that ritual, the Inca carried mummies instead of saints, especially the mummies of their kings.

When Pachacuti died, in 1471, he wasn't buried, he was mummified.

The exact process is unknown. One theory suggests his body would have been gradually freezedried: left out in the searing sun by day, and, alternately, frozen at night.

Through this repeated heating, freezing and thawing, the corpse would have become completely desiccated.

Curiously, this is similar to how the local Quetchua people preserve llama meat. The result is "jerky," which is one of the few Quetchua words used in English.

Once preserved, Pachacuti would not have been entombed. Instead, he would have continued to play an active role in the politics and rituals of the Inca world.

Drawings made by the Incan artist, Guaman Poma, confirm the use of mummies in this way.

JOHAN REINHARD: We don't actually have a mummy of an Inca emperor, but we have descriptions of them, and we know that they were taken out during major festivals and paraded. We know that they had attendants who would shoo away the flies and give offerings every day: food offerings and drink to the mummies.

In other words, they were worshipped and believed to still play a role in the community.

NARRATOR: Care and handling of the mummy would have fallen to a group of family members, called the panaca, who also took control of all the king's royal estates.

But, over time, even Pachacuti's panaca could have run short of resources. Work at Machu Picchu may have slowed, then stopped altogether. The descendants of Pachacuti had more pressing concerns.

Even before the Spanish conquest, smallpox came. It was followed by a bloody civil war that left the Inca Empire weakened and fragmented. Barely 60 years after Pachacuti died, the Inca Empire finally collapsed under the Spanish invasion.

JOHN VERANO: When the royal families were...had lost their power, they were disorganized; there was civil war. There was massive destruction of sites.

And the people at Machu Picchu, probably, at some point, just said, "Well, nobody is coming to visit." And the site really had no reason to exist at that point.

NARRATOR: By then, it is likely that all but the loyal servants had forgotten Machu Picchu. And, after time, even they probably just drifted away. So the Spanish probably never heard about Machu Picchu and, more importantly, never found it.

It was, for us, the luckiest mistake. It meant that Machu Picchu was left untouched, one of the only major Inca sites to remain intact.

While it still poses confounding mysteries, it also holds great promise as new technologies and finds allow us to come to terms with the ghosts of Machu Picchu.