Original subtitles

NARRATOR: Satellites above an iconic American city

make an alarming discovery.

Vast ruins stand out in the middle of the Saharan Desert.

Drones uncover a puzzling stone mystery perched

high in the Andes.

And a massive,

modern metropolis in the Mongolian desert totally deserted.

- Where is everybody?

NARRATOR: Everywhere we look on our planet,

there's evidence of the past.

In nature. In buildings. In relics.

Each holds a mystery that technology now allows us to see from above.

What new secrets are revealed?

Across the globe, more than half of the world's population -

4.4 billion people - live in cities, each full of hidden

stories and secrets that are best revealed with a view from above.

Flying high above New York City,

cutting edge technology discovers something shocking.

InSar satellites - designed to detect

variations in the earth's surface - uncover an alarming increase in

the rate of a bizarre and disturbing phenomena called 'subsidence'.

- Subsidence is a geological term for the downward vertical

movement of the Earth's surface.

Basically it's sinking. - Hold on, did you say sinking?

So New York City is sinking?

- And they found this out - from the sky? How's that work?

- InSAR satellites are especially good at detecting

and measuring subsidence.

With each pass over the earth, they track ground deformation

and changes that occur gradually over months or years.

- They can cover huge areas, making them

ideal for urban environments like New York.

- Subsidence has been occurring where New York City now sits

since the end of the last ice age.

As the ice sheets retreated, the land once covered by the ice,

north of the city, began to rise up and the land just

south of the ice, where New York City is today, began to sink.

That slow response to melting of the ice sheets continues today,

at a rate of about 1 to 2 millimetres every year.

- Okay, so what's the big deal?

NARRATOR: Tracking from the skies, the satellites over New York

find parts of the city are sinking at a pace of 4mm a year -

that means the Big Apple is going down far faster than expected.

But what is behind this terrifying drop?

What kind of forces can sink a city?

Could this be caused by sinkholes?

- Over the past decade, we are seeing more and more of them

across the world.

And they're getting bigger, deeper and a lot more dangerous.

- Sinkholes tend to form in cities for one of two reasons:

either a section of a street collapses

because of a water main break or an old pipe giving way or,

you get changes to natural water-drainage patterns.

- In recent years, more and more sinkholes have left enormous

gaping pits in downtown Manhattan - the middle of East 89th

Street on the Upper East Side and Riverside Drive on the

Upper West Side being two examples that happened only days apart.

- It's believed that these new multi-foot-deep

depressions are the result of the city's deeply outdated

underground infrastructure, which has an average age of 66 years.

- And with 7,000 miles worth of water mains,

that's a lot of old pipes posing silent threats.

- So could the increasing size

and frequency of sinkholes be bringing down the city?

- Unlikely.

Deep and dangerous as they are, these sinkholes alone are not

enough to take down a city the size of New York.

- So what is happening in New York City?

NARRATOR: Perhaps there's a clue in another sinking city

almost 12,000 km away, Shanghai, China.

- China's most populated city has dropped more than six feet

since 1921.

The result has been devastating flooding in the city

and getting worse every year.

- The problem stems from Shanghai's rapid 19th century growth,

stretched to supply factories and drinking water to a population

that by 1900 had tripled to more than one million.

Groundwater that had supported the Chinese trading port quickly

became strained.

- And it kept going.

The problem got so bad by the 1950s

and 1960s that the ground was sinking by four inches a year!

- The government took action in 1963,

banning the overuse of wells but the decline continued

- by the mid-1960s the city had sunk about 16 more inches.

And it's only going to get worse!

Official projections say water levels could rise several

inches by 2050, threatening waterfront areas.

NARRATOR: Could this be happening to New York City?

Is the Big Apple's drinking causing its sinking?

Is the loss of groundwater the problem?

- It's unlikely that this is just a groundwater thing.

Groundwater management has been a part of New York City's

infrastructure for decades - between 1996 and 2007,

the city transitioned away from using any groundwater

wells as part of their drinking water supply.

- So, if it's not water going out maybe it's water coming in

that's the problem?

NARRATOR: The satellite view over New York City,

shows that the areas sinking fastest are the edges of the city,

where New York lies less than 2 meters above sea level.

- Could the rising sea levels be pushing the city down?

It's no secret that storms and hurricanes have

increased in ferocity in the past decade with devastating results.

- In 2012, Hurricane Sandy killed more than 40 New Yorkers,

destroyed approximately 300 homes,

and left tens of thousands of people without power.

- In 2021, Hurricane Ida left more than a dozen people dead in

New York City, many after they were unable to escape flooding basements.

- In New York City, sea levels have risen a foot over the last

100 years - that's a rate of about 1.2 inches per decade.

- That may not seem like a large increase, the implications are huge.

Sea levels are expected to rise anywhere from 8-30 inches

by the 2050's.

And as much as 15-75 inches by the end of the century.

NARRATOR: Are rising sea levels destined to consume -

and sink - New York City?

- While rising sea levels are very much a threat, a recent study

of 99 coastal cities around the world found that subsidence - the

sinking of the ground - may pose a bigger problem than sea-level rise.

Why?

Because most cities surveyed,

the land is subsiding faster than sea levels are rising.

- So what's causing this increase in subsidence?

NARRATOR: Perhaps a clue lies closer to home over 1000 km

away in Chicago.

- Scientists from Northwestern University in Chicago have

discovered that increased temperatures underground is

making Chicago's clay soil contract, causing the Windy City to sink.

- What they discovered is that the heat escaping from basements

and parking garages, sewers, tunnels,

other underground infrastructure is actually shifting the landscape

and its causing Chicago to slowly - but definitively - sink.

- Much of Chicago was built on a glacial lakebed,

which means very clay-ey soils.

This type of soil can swell when heated -

causing buildings built on top it to settle faster than normal.

- The study showed that the ground could swell

something like 12 millimetres,

and the structures could sink something like 8 millimetres.

And that may not sound like very much but

those small changes can be devastating for buildings

that are not designed for that kind of movement.

- Nobody talks about this, but it's a real thing -

scientists call it 'underground climate change.'

- Could New York City be heating itself to destruction?

NARRATOR: In 2023, researchers from the US Geological Survey

and the University of Rhode Island decided to investigate.

- What the team studied were InSAR satellite images collected from

orbiting satellites that actually map subsidence all across the city.

- The results showed as expected,

that all of New York City as a whole is sinking 1 to 2 millimetres

every year because of post-glacial relaxation.

But, and this is the big part- they discovered that those

parts of the city where big buildings are built on fill

and sediment are sinking faster, up to 4 millimetres every year.

- Could New York City just be too heavy?!

NARRATOR: To test this theory, the scientists calculated

the collective weight of more than a million buildings in New York City.

- They estimated that

NYC's buildings collectively weigh 1.68 trillion pounds -

equivalent to roughly 1.9 million fully fuelled Boeing 747s.

- And, that's just the buildings!

That's not the contents, the people, the vehicles - all that other stuff!

NARRATOR: To determine what part of the cities were bearing

the most weight,

the scientists divided the city into a grid of 100-by-100-meter squares.

This allowed them to calculate the downward pressure

caused by the weight of the buildings, across the whole city.

- The research suggested that indeed,

the weight of buildings is causing increased subsidence in those

parts of the city vulnerable to this immense pressure.

- The skyscrapers anchored to underlying bedrock

in the upper parts of the city, not much of a subsidence problem.

But, the hundreds of buildings sitting on spongy

materials like clay and artificial fill on the lower lying

edges of the city those are very prone to compression.

- And it's important to remember that this is

happening in a city where the sea level is

projected to rise between 8 and 30 inches by 2050 - this extra sinking

factor increases New York City's vulnerability to coastal storms.

- The likelihood of parts of New York City eventually being

permanently under water is inevitable.

The ground is going down, and the water's coming up.

At some point, those two levels are gonna meet.

- Because we have rising sea levels and sinking

buildings at the same time, this means that coastal flooding

is gonna happen a lot faster than predicted by existing models.

- It's a really scary projection - but, thanks to what we now know,

cities like New York can much better plan and actually prepare

for the long-term impact of sea level rise and coastal subsidence.

NARRATOR: Revealing these hidden forces sinking New York City

and other cities like it around the world before its too late is

only possible with a high tech view from above.

In the deep central Sahara, in the African country of Niger,

a view from above reveals a sprawling, empty, ancient mystery.

- What the heck is this place - it looks like a giant ant colony!

- It looks like a small, fortified city -

but slap bang in the middle of nowhere!

- And it looks totally empty!

- Abandoned cities are not unusual in the desert.

- But most desert settlements found in this

part of Africa are simple in their layout

and scope - this one has fortified walls, watchtowers and passageways.

NARRATOR: This unusual site is called the Ksars of Djado.

Built between 800 to 1000 years ago, the architects of this site

have long been a mystery - no one knows who built it.

- It would have been an enormous undertaking,

it would have required you know, a lot of elaborate planning,

a lot of skill, a lot of time to create what is a spectacular

fortress in the heart of northern Africa.

- Why go to so much trouble to create a massive walled

fortress like this, in the middle of nowhere?

What was it meant to protect? Why are the Ksars of Djado, here?

NARRATOR: A clue to this mystery may lie with another abandoned

desert city almost 3000 km away in the Golan Heights where

a view from above reveals the desert fortress of Nimrod.

Like the Ksars of Djado, Nimrod lies empty

and silent - another walled city left to crumble in the sand.

- Dated as early as 30 CE, Nimrod was built to guard a major access

to Damascus, a key centre of trade on the Trans-Saharan trade route.

- The Trans-Saharan trade routes connected the Mediterranean

coast to the West African savannah and the sub-Saharan region.

- These routes were used to transport a variety of goods,

including gold, ivory, salt, and slaves.

- It's impossible to overstate the significance of these routes,

in African history - really, in world history.

They were also a major source of cultural exchange -

traders brought goods, ideas,

and technologies from one part of the world to another, leading to

the spread of religions, languages, and other cultural traditions.

- One example of a technology that was introduced to Africa

through the Trans-Saharan trade routes is the camel, which was

domesticated in the Middle East and brought to Africa by Arab traders.

- The camel was an invaluable tool for trade and transport

in the Sahara Desert, as it's able to travel really long distances

across the desert with minimal water and can carry heavy loads.

So the use of camels completely revolutionizes trade

and transport in the region and it

also facilitated the growth of the Trans-Saharan trade routes.

- At the peak of the caravan trade, the average caravan was

made up of 1,000 camels and some caravans were as large as 12,000!

NARRATOR: Could this be why Djado is here -

built as a fortress to protect a crucial trade route?

- It's possible, because Djado was once smack in the middle of this

complex network of trade routes all across Africa and the Middle East.

- It's perfectly situated on this busy route, the Ksars of Djado

would have thrived as a bustling and prosperous centre of trade.

- The city was so successful, it swelled to be the biggest

of its kind - it would have been a jewel of commerce in the desert.

- It's sorta like an early, Saharan Las Vegas!

- But, if the Ksars of Djado were so big and so strong

and so prosperous then why did the city basically just disappear?

NARRATOR: Could a closer look at Nimrod from above reveal more clues?

- We can see several structures here that were clearly

created to defend the city from attacking raiders.

- And, Nimrod has a well documented history rife with conflict

and destruction, underlining the reality that a city this rich,

is a target for conquest.

- Nimrod withstood a lot of attacks,

a lot of raids over the centuries, but it was finally

sacked for good when the Assyrian empire fell to a coalition that was

led by Babylonia and Medea at the end of the seventh century BCE.

- Is that what happened to these grand and wealthy Ksars of Djado?

NARRATOR: Perhaps there's a clue almost 9000 km away,

in the Gobi Desert of Western Inner Mongolia with another

abandoned desert city, Khara-Khoto.

- Founded in 1032 CE as the capital of the Western Xia Dynasty,

this city was also a thriving trade centre,

located on an important trade route through Asia.

- But, just like Nimrod,

the rich city caught the eye of unfriendly invaders.

It was captured by Genghis Khan in 1226.

- Khara-Khoto actually flourished under Mongol rule.

During Kubla Kahn's time, the city expanded to 3 times its original

size, and was even mentioned by Marco Polo in his travel logs.

- Under the Mongols, the people were able to enjoy a peaceful

existence for about 150 years, and that's

until the Ming dynasty turned up in 1372 and laid siege to the city.

- Now, no one knows exactly how Khara-Khoto fell, but the most

commonly accepted theory is that the Ming rulers diverted the

Ejin River, the city's only water source, that flowed just outside

the fortress thus denying the city's troops and inhabitants water.

- Is this what happened to Ksars of Djado?

Did an outside enemy wipe out the people here?

- It doesn't look like it.

While the city was almost attacked in the 18th

and 19th century by all these waves of nomadic raiders, it wasn't

until the arrival of the French military in 1923 that the

Ksars of Djado lost their independence.

NARRATOR: If the people of the Ksars of Djado were not starved out

or killed by a foreign power, why and how did they disappear?

- How did this spectacular desert city end up becoming a ghost town?

NARRATOR: An answer may be found just over 1600 km away in Mali,

home of the legendary Saharan city, Timbuktu.

- Once dubbed the 'city of gold' Timbuktu was a prosperous

commercial hub for the ivory, salt and gold trades.

It was also, a hub for the slave trade.

NARRATOR: Timbuktu is still going today - but barely.

- Timbuktu is struggling to survive and it's this modern struggle that

holds a crucial clue to the downfall of the ancient Ksars of Djado.

- It's being eaten up by the desert.

- When it was built in the 5th century BCE, Timbuktu,

like Djado, thrived in a lush liveable landscape.

But now, the desert is moving in and the city is

suffering from rapid desertification.

- Desertification is an increasingly widespread problem as climate

change modifies weather patterns,

leaving people to deal with hyper arid conditions.

- The Sahara Desert is no exception - scientists have observed

that in the last century, the Saraha has expanded by 10 percent.

And the problem is especially bad in Timbuktu - in Mali,

the Sahara there is expanding at a rate of 48 km every year!

- So could a similar thing have happened to Ksars of Djado?

- It's possible.

These ruins are 800 to 1000 years old - and that means that they

were built at a time when this part of the Sahara was much wetter.

NARRATOR: And just like Timbuktu, relentless desert swallowed Djado.

- So it's very likely that what pushed people to abandon

Djado was the lack of a clean water supply.

You had this lush landscape, and then it all turned into desert,

and that environment was just too harsh for humans.

- Djado was then pretty much unlivable,

and by the early 1900s, it was abandoned.

- The people are long gone but the Ksars of Djado were

so well constructed that the abandonment of the city did

not mean it was destroyed.

NARRATOR: Isolated from the outside world and built to last,

the great Ksars of Djado stand tall today.

A long-forgotten ghost city, its secrets

uncovered by a view from above.

On the densely forested slopes of the eastern Peruvian Andes,

over 600 km north of Lima

a view from above reveals an ancient wonder.

Sitting high on the mountain ridge, 3000 meters

above sea level, this mysterious stone site is known as Kuelap.

- Look at that wall!

NARRATOR: This epic structure surrounds all of Kuelap with a

length of over 1000 meters - and, in some places stands 20 meters tall.

- It's constructed from limestone blocks -

some with an estimated weight of 3 tons - that's as heavy as a hippo!

- That wall is on the scale of a fortress - is this structure

an abandoned military base or the site of an old castle?

NARRATOR: Is Kuelap the ruins of a fortified city?

- Even though it may look, uh, as a defensive construction,

we have to take into consideration that there is no parapet.

- Okay so if there's no parapet like you'd usually

see around a fortress - what about that huge, long wall -

isn't that also a classic fortress feature?

- In some parts, the surrounding wall is 20 meters high.

In other parts it's only six.

NARRATOR: Some parts of the wall are far too low to provide any

protection - and there's something else missing at Kuelap,

something crucial to survival.

- There's no water inside.

Water has to be brought from the springs that we

have around Kuelap or from the river.

So knowing that there is no water reservoirs, no springs inside,

we can completely disregard the idea that Kuelap was a fortress.

NARRATOR: So what is this place?

A view from above reveals a network of strange stone

circles across Kuelap. Could these mysterious rings provide any clues?

- Did they hold water - is this like an ancient spa?

Or were they food storage structures,

like modern day farm silos?

- Those stone circles are really intriguing-

maybe they have some sort of ritual purpose?

NARRATOR: Perhaps clues can be uncovered

halfway across the world at Mycenae in Greece,

where a view from above reveals another set

of mysterious stone circles.

Excavations at Mycenae revealed that these large stone

circles are grave sites.

- Those circles contained skeletons from the royal families -

accompanied by a treasure trove of their personal stuff.

- So could the strange stone circles at Kuelap have been

part of a burial site like we see at Mycenae?

Could they be tombs?

NARRATOR: Investigations at Kuelap have uncovered a clue,

human remains.

- That is definitely related to the importance to venerate

our grandfathers and great-grandfathers even after

they have died a long time ago.

- So if human bones were found in these circles,

these must be the remains of tombs.

NARRATOR: But a closer look at these circles reveals something

unexpected.

- There's evidence of some kind of wooden structure where

they could put the bed where they slept

and also where they can store other goods.

Then we have the kitchen area where the fire is located.

- It's basically a multi-familiar building that is a circular

construction that has a diameter that can vary between five

and 10 meters.

There's some characteristics that are always inside these huts.

The tomb where they kept some bones of their ancestors is usually

located in the centre of the building.

NARRATOR: There are more than 400 of these multi-family houses in Kuelap.

- If we make the math with the amount of people that can

live in one of these huts, we are talking about at its height,

a population of around 2,500 people living in Kuelap.

- So if those circles were once houses to a lot of people,

who were they?

NARRATOR: A wider view from above reveals another clue,

a dramatic rectangular structure.

- This one is the biggest building in Kuelap. It's called a Kallanka.

It's a symbol of power of the Incas.

- Finding the ruins of Kallanka is like finding a giant sign

that says, 'The Inca were here'.

It's an unambiguous stamp that this place was definitely

part of the Inca Empire.

NARRATOR: So did the Inca build Kuelap?

- Kuelap isn't very far from the world-famous Machu Picchu

which was built by the Inca - is this another one of their creations?

- According to the radiocarbon dating's that we have,

Kuelap was built around 600 AD.

- Machu Picchu is dated to almost a 1000 years later than that -

so Kuelap was built long before the Inca started up.

NARRATOR: But if the Inca aren't behind this ancient site, who is?

- Kuelap and all the settlements around were

built by the Chachapoya culture.

Chachapoya is a generic name that the Incas started

using for the people that live in this huge

area of approximately 200,000 square kilometres.

- There's a lot of mystery surrounding these people

and their culture.

- We know they thrived in a region of Northern Peru from about 900

to 1400 CE, but they didn't have a written language, so much

of what we know of them comes from studying the ruins they left behind.

- But, wait, if the Chachapoya built Kuelap,

then what's with all the Inca stuff here?

NARRATOR: From 1438 to 1533 the Incan Empire grew rapidly -

becoming the largest empire ever seen in the Americas.

As they expanded north through Peru, the Inca conquered Kuelap

and ruled over the Chachapoya people.

But around the mid 16th century, Kuelap was suddenly abandoned.

- Why would the mighty Inca Empire go to all

the trouble of conquering this place,

putting up all these buildings and then just abandon Kuelap?

NARRATOR: Perhaps there's a clue more than 12,000 kilometres

away near the Sea of Galilee, with another abandoned city - Gamla.

- Gamla has plenty in common with Kuelap - a defensive stone wall,

residential housing and dedicated space for rituals and celebration.

NARRATOR: Like Kuelap, Gamla was a thriving city but in the 1st

century Roman soldiers attacked, leaving destruction in their wake.

- Was Kuelap abandoned because it was invaded?

- Is this what led to Kuelap's abandonment?

- That's exactly what happened here.

In the mid-1500's, the Spanish conquered the area

and ended the Inca's 70-year reign in Kuelap.

NARRATOR: The conquered Inca and Chachapoya were rounded up

and Kuelap was abandoned.

Since then - Kuelap has stood frozen in time,

an ancient testament to a once mighty city.

But now - the view from above reveals Kuelap has a more

modern mystery to be solved.

- One of the mysteries of La Fortaleza de Kuelap is

the collapse of the southern perimeter wall in 2022.

NARRATOR: A huge stretch of this giant wall,

almost 30 metres long - simply gave out.

- People immediately began to ask if this monument is a thousand

years old and has withstood time, why is it falling down now?

NARRATOR: What modern phenomena could be causing this

kind of damage to the wall?

- Is Kuelap a victim of natural forces?

NARRATOR: Peru is located in the Ring of Fire -

where more than 80% of the world's largest earthquakes occur.

- The ring of fire is this giant belt that wraps around the

Pacific ocean where lots of our planet's tectonic plates meet.

When they slip beneath each other,

that's when you get all kinds of earthquakes.

NARRATOR: Two earthquakes did hit the region in 2022 -

but neither were strong enough to cause this level of destruction.

- So we can cross earthquake damage off the list.

Why else would the wall at Kuelap come down so quickly -

especially after standing strong for centuries?

NARRATOR: Perhaps, the collapse of the wall was caused

not by outside forces, but instead, forces within.

- We have elements here,

some clues to solve the mystery of the history of the collapses here.

Water has accumulated behind this wall,

it's been turned a little bit into a dam, and this interior core

made of mud and stone, has gone from solid to be a little more plastic.

And it's sitting on a sloping terrain. So it begins pushing down.

And the perimeter wall, however solid

and massive it is, cannot hold the weight of this plastic core.

And this is how the collapse has happened.

We have solved one mystery.

Now we have confirmed that water infiltration is the ultimate

cause of the collapse of the perimeter walls.

But obviously, another mystery remains. Why now?

- What could possibly cause this wall,

that's stood strong for about a 1000 years, to just start crumbling?

NARRATOR: Scientists believe the cause of this problem

comes from above.

- Because of the great amount of precipitation in this area,

one of the main theories is the infiltration of rainwater.

- Rain? That is the culprit?

I can see how an earthquake might cause damage like this, but rain!

Is it really that powerful?

- The rainy season here is very heavy,

perhaps up to 3000 millimetres a year.

NARRATOR: But why now, after 1000 years,

is rain such a threat to the wall - and all of Kuelap?

- So, we use data from some weather stations

and mostly satellites to reconstruct the patterns of precipitation

for the last four decades.

And that was a real discovery.

The precipitation has been growing over time,

it's about 4% higher today than it was in the 1980s.

And out of seven historically high precipitation

months in those 40 years, four occurred in the last five years.

So there is an increasing trend,

and that is becoming more critical in the last few years.

NARRATOR: One year after the collapse of the wall,

Peru is experiencing what's called a Coastal El Nino, a weather

event that's expected to bring more torrential rain to the area.

- The amount of water that it's receiving today,

due to climate change, may be exceeding its capabilities.

NARRATOR: Recent satellite imagery has revealed that the surface

water off the coast of Peru is about 6 degrees higher than normal.

- When you've got warm water like this, it adds heat to the air,

which means it can hold more water, which means bigger rainfall.

- And bigger rainfall means more water is

getting into the core of Kuelap's wall.

- If we don't mitigate the infiltration,

the core is going to become plastic and push the perimeter walls

out, and the whole monument is going to collapse.

- It's a race against the clock - can you figure out

how to protect the site before the next round of catastrophic rain.

- It would be such a tragedy if the site of Kuelap washed away -

there is so much history and still so much to be discovered there.

NARRATOR: Scientists are determined to preserve this magnificent

city - and thanks to their research, they now know what needs to be done.

- We should be mitigating the infiltration.

And when that has stabilized,

then we can reconstruct the perimeter walls.

With the goal of preserving this for future generations,

for everyone to enjoy.

NARRATOR: A mystery solved - and a discovery that could

help save an ancient city all with a view from above.

High over the arid plains of Northern China, in the remote

desert of Inner Mongolia a view from above reveals something unexpected.

- It looks utterly abandoned - what happened here?

- It's totally empty! Where did everyone go?

- It totally looks like something out of a science fiction movie!

NARRATOR: The official name of the city is 'Kangbashi New Town'

but it's often referred to by the area in which it's built - Ordos.

The story of Ordos begins in the early 2000's

when the Chinese government began to build

the city in the Ordos Desert, spending one billion dollars.

- Ordos was designed to provide everything a modern city

could possibly need or desire,

all for a population of at least a million people.

- So where are they? Where are all the people?

- It looks apocalyptic - like, something just wiped everyone out!

- Was this city emptied by a sudden, massive disaster?

NARRATOR: Perhaps a clue can be found more than 6000 km

away in Ukraine, home to one of the biggest disasters in modern times.

- On April 25 and 26, 1986, a faulty Soviet

reactor at the Chernobyl nuclear power plant exploded.

NARRATOR: As the radiation spread through the air,

it covered more than 40% of Europe.

- Today, almost forty years later, there is still a 30 kilometre

'exclusion zone' around the plant - scientists estimate this

zone around Chernobyl will not be habitable for up to 20,000 years.

- It looks eerily similar to Ordos all these empty buildings,

sort of frozen in time and empty.

- Did a similar disaster happen to Ordos?

- No records exist that Ordos suffered

anything like Chernobyl - the city isn't a designated danger zone

and is actually perfectly safe to live in.

- In fact, the region is quite prosperous.

I mean yes, it's essentially a desert,

but the landscape is rich in resources - particularly, coal.

- And that's why Ordos was built here.

A coal boom in the early 2000's compelled the local

government to splurge on this new development.

- So, if Ordos is considered a completely safe place to live

and it was supported by a rich industry, why is it empty?

NARRATOR: There may be a clue far to the southwest in Namibia,

in another abandoned desert city.

- Once a prosperous diamond mining town, Kolmanskop was abandoned

when the diamonds ran out and better resources were found elsewhere.

- And ever since, the fast-moving Namibian Desert has been

closing in and literally, swallowing up the town.

- Satellite observations found that the average rate at which

the dunes in this area moved ranged from 7 to 32 meters per year!

- The Kolmanskop is not alone.

The Namibian desert has been swallowing more than just the towns.

NARRATOR: One of the most famous examples of the desert's power to

consume, can be found over 400 kilometres away,

on Namibia's Skeleton Coast.

- The waters off this place are famous for their strong currents,

dense fogs, and treacherous sand banks that constantly move.

These extreme climatic conditions

when combined with strong sandstorms have been considered

the cause of the sinking of over a thousand ships.

NARRATOR: The eerie remnants of long-lost ships and stranded

sea creatures lies scattered across this desolate landscape.

- Is something like this happening to Ordos?

- Is Ordos being buried by sand?

NARRATOR: A view from above shows that Ordos is on the edge

of the Gobi Desert - the fastest growing desert in the world.

- Between 1975 and 2017,

China's deserts expanded by an astonishing 21,000 square miles.

- That's equivalent to more than 10 million football fields!

- The catalyst for this is deforestation.

All the upheaval and removal of huge, ancient roots means the

soil isn't held together and is more vulnerable to natural wind erosion.

- China has tried planting trees to hold back the desert with a 'Green

Great Wall' but a fifth of the trees planted so far have been planted

in places they don't naturally grow, so they've already died.

- So is the fast-approaching desert what forced people to flee the city?

NARRATOR: But a view from above reveals massive reservoirs

supplying Ordos City.

- So while there's no question the desert is expanding,

between the solid, modern buildings and the giant reservoirs,

it's unlikely that people would think the approaching desert

was a problem.

NARRATOR: So if people didn't flee

because they feared being swallowed up by the desert then why?

What turned the massive city of Ordos into a ghost town?

- It doesn't appear that the city was abandoned

because of some kind of disaster - man-made or natural.

- So where is everybody?

NARRATOR: Perhaps an answer to this mystery lies more than 1000 km

away, in another strange city in China.

- Oh that is bizarre! I mean just look at that!

I mean it's a total replica of an English town -

complete with pubs and old-time English architecture.

- This just gets weirder and weirder.

NARRATOR: This is Thames Town.

Created in 2006, the town was meant to be home for the thousands

of people who live and work at nearby universities.

- The city was expensive to build - an estimated 635 million dollars.

And, expensive to live in. Too much so, in fact.

- Thames Town was almost as expensive to live in as London

itself, now that is saying something!

- It's bonkers. Really!

I mean, how much money did they think people who live

and work at Universities make?! - In the end,

the government only managed to get a few thousand people to live there.

NARRATOR: And Thamestown is not the only time this happened -

another city built to look like Paris, France,

also failed because no one could afford to live there.

- So, is this what happened to Ordos?

Is this massive city virtually empty

because no one has enough money to survive there?

- I think we're getting warmer.

It cost well over a billion dollars to build Ordos.

That meant developers needed high real estate prices to get

a return on their investment.

- But, people didn't sign up in droves the way the builders

thought they would.

- So, the developers were forced to scale back plans for a population

of 1 million people but the actual population only reached 100,000.

- And so you have what, 100,000 people being asked to make

up the shortfall so developers could recoup their losses?

Not a great plan -

This drove the prices of everything through the roof.

NARRATOR: And it got worse - at one point,

property prices plunged so badly that many developers went bankrupt.

- The Ordos project essentially fell flat on its face.

They just couldn't get enough people living there to sustain it.

- Looking over the city,

it's easy to see why the unfinished houses and the vast, empty,

dusty blocks of a city with insanely expensive real estate and

impossible cost of living, didn't exactly attract droves of families.

- The one thing that did make a difference was education.

Over the past several years China has worked hard to make Ordos

more attractive.

The most successful of these efforts was bringing in good schools.

- Education is highly valued in China and the promise

of access to good schools has started to lure families to Ordos.

- Slowly, the city is coming back but it is still

nowhere near the epic metropolis it was designed to be.

- Ordos is the ultimate lesson in arrogance and greed in the desert.

NARRATOR: An epic urban folly, revealed only by a view from above.

From a modern metropolis dangerously close to the edge,

to an ancient walled city in the clouds, to a mysterious desert

city losing the battle with nature and an abandoned urban disaster.

Mysteries of these great cities clearly

uncovered with a view from above.

Subtitles by Sky Access Services