Mexico City World's Busiest Cities

More than half of us now live in cities,

and more of us are moving in.

By 2050, two-thirds of the planet will be city dwellers.

There's people going this way, people going that way.

It's bonkers!

We're exploring four iconic cities in all four corners of the world.

This cycle rickshaw is coming the wrong way towards us.

These are places bursting with life.

Crowded, chaotic and complicated,

they're also under pressure.

HORNS BLARE

All right, mate.

We're going behind the scenes...

..to uncover the hidden systems and armies of people

running some of the greatest cities on Earth.

This time, we're in Mexico City.

A sprawling megalopolis, fuelled by optimism and enterprise.

We're going to show you

how this often makeshift and haphazard city works.

Uncovering the incredible story of how it survives

its many daily battles.

Historian Dan Snow finds out what it's like

to build big in a deadly earthquake zone.

I'm feeling more confident about Mexico City's tallest building.

Even if there's an earthquake, we're going be fine.

You're going to be perfectly safe.

Journalist Ade Adepitan looks for new sources of water

in one of the world's thirstiest cities.

That looks clean to me.

Yeah, it is.

It's fantastic. I'm so impressed, I am.

And I'm Anita Rani.

I'll be learning how they're trying to stop this massive megacity

from drowning in its own waste.

Oh, it's a sofa!

There's a whole dashboard here.

I mean, it's horrendous,

but a vital part of any city.

Join us for the adventure of a lifetime

in The World's Busiest Cities.

Mexico City -

home to nearly 22 million people.

And where better to start than in its beating heart - the streets?

-Now this is a proper locals' market, isn't it?

-Yeah, exactly.

So, this is where you're going to get absolutely everything you need.

Oh, my God.

Street food is almost a religion here -

a mix of the cultures that built this city.

DAN LAUGHS

Amazing. We are in the home of the chilli.

I know.

VOICEOVER: This is one of 1,000 tianguis, or open-air markets,

that have been here since the city began.

Even the name dates back to the Aztec Empire.

-Right, you're going to try that.

-I...

-OK!

-OK.

VOICEOVER: When the Spanish arrived in the 16th century,

they called this food antojitos, or "little cravings".

It's still a big part of how this informal city is fed.

Gracias, muchas gracias.

Street food is what it's all about in Mexico, Dan.

That is so...

It's terrifying. Go on, you go first.

She orders it, she makes me try it -

that's how this relationship works!

-Gentleman first.

-Oh, God.

Let's hope it's better than it looks.

Oh!

How is it? I'm going to try it.

-Delicious.

-Is it really hot?

-It's really hot.

-Crazy woman!

-Have I put too much chilli in it?

Mm! That chilli is a killer.

Thanks for the chilli, yeah.

You can't come to Mexico and not have chilli!

Home to an incredible one-fifth of Mexico's total population,

this is a city that has come to define urban sprawl,

with self-built homes clustered on its scattered hillsides.

These colourful markets are where people come together.

What I love about this place is, already, it can only be Mexico,

you couldn't be anywhere else in the world - what people are eating,

what they're wearing, what they look like.

Even though it's so close to the United States,

you expect American culture to be down here.

In fact, it's just brilliantly vibrant, Mexican...

-And so distinct.

-Yeah, it's so distinct.

-Yeah.

And everybody's sitting down and eating.

There's food stalls every five yards.

Mexico City is one of the most challenging

urban environments on the planet.

It's grown at a staggering pace and is struggling to cope.

HORNS BLARE

It's crowded, it's congested...

..there are problems with water and sewerage,

and this haphazard city sits in a major earthquake zone,

where parts of it are sinking around ten centimetres every year.

VOICEOVER: But, sitting here, you'd never know it.

I think it's interesting,

because it is a city with massive ecological and other problems,

and yet people don't seem very fussed about it.

They're just getting on with it. They're enjoying it.

And we're in the capital city, and yet this feels like

we could be in, sort of, rural Mexico somewhere,

some local market.

See, Dan?

People might think that this is some sort of cliche,

but it's real, it happens.

People just turn up and start playing trumpet.

We're going to find out what really makes this megacity tick

and experience the hidden systems and strength of spirit

that allow it to defy everything its nearly 22 million inhabitants

and Mother Nature can throw at it.

There's no mistaking it now, Dan. We are in Mexico.

-Whoo!

-Wahey!

Mexico City sits right at the centre of the country it serves as capital,

high on a plateau, at 2,240 metres above sea level.

Founded on a lake that was drained by the Spanish conquistadors,

the city exploded in the 20th century,

spilling over from its historic core into a metropolitan area

now stretching over nearly 1,000 square miles -

the largest in the entire Western Hemisphere.

We're splitting up to explore this epic sprawl.

While Anita and Dan travel deeper into the city,

I'm heading to the suburb of Neza

to find out just how this city grew and grew and grew.

Now, I've come here because this place

has got a really fascinating history.

Now, I've been told that all these colourful houses around here

have been self-built, brick by brick, by the residents.

I haven't been here that long,

and this place is already giving off this really interesting vibe.

Now, I'm going to meet one of the families that've been here

since the early days,

just to find out a little bit more about this place.

If you need somewhere to live in Mexico City,

you build it yourself.

Incredibly, more than half the architecture here

is built without regulations

ensuring basic construction standards.

-Hola.

-Hola. Buen dia.

-Buen dia.

Hola. Benito...

-VOICEOVER:

-Benito Perez and his mother-in-law, Gloria Lopez,

have lived in this house for decades.

IN SPANISH:

In Mexico City, more than 60% of people

live in areas known as colonias populares -

informal, unregulated settlements.

It's how Neza started.

Oh, it's just amazing.

I wouldn't know where to start when it comes to building a house.

But, you know, these people, they're just so...

They're so motivated.

Wow.

In this house, there's 22 people that live here,

and four generations of their family,

which is incredible.

You know, it's like anywhere in the world, man -

you want to make your house a castle, don't you?

-VOICEOVER:

-I'm surprised to discover that the family

don't just live here -

Benito also runs his shoe business from the house.

Look at that. He's just making a shoe...

..right in front of my very eyes.

-VOICEOVER:

-Benito tells me that businesses like his

are a common feature in homes across the city.

Households, they'll either be selling shoes,

they'll be making something, and then they'll take it

to the tianguis, the local market, the portable market,

to earn money for their families.

So the house is more than just a house.

It's a business, it's everything for them.

-VOICEOVER:

-I feel humbled that the family has invited me

to stay for lunch.

In Mexico, food is a serious business.

-VOICEOVER:

-It's my chance to meet the rest of the family,

including Benito's wife, Sandra.

You're going to speak English to me, yes?

Si. Poquito!

THEY LAUGH

-VOICEOVER:

-There's Grandad Bernabe, who built this house,

Benito's daughter Lupita,

and the rest of the family.

This is really cool, actually, to have traditional Mexican food

in a house that was built by this family.

I mean, you can't get more authentic than that, can you?

They're going to pray.

-Amen.

-Aproveche.

-Gracias.

Oh...!

Si?

-VOICEOVER:

-Benito wants to show me photos from the early 1970s,

taken when Grandad Bernabe was building the house.

THEY LAUGH

Wow. Benito learned from his father-in-law.

But his father-in-law learned from watching other people.

That was it, you know. Just watched other people and decided,

"I'm going to create this, my dream."

It's incredible.

Just 40 years ago, Neza was on the fringes of the sprawl.

Now, more than 1 million people live here,

and the settlement has been absorbed into Mexico City.

It's a testament to the spirit of its citizens.

Que paso? Que tal?

It's a lot of character going on in this place.

As people build houses further and further out,

their journeys into work get longer and longer.

I've been thrown in at the deep end,

trying to figure out the daily commute.

HORN BLARES

All right, mate.

Buses here are cheap and plentiful.

In fact, this is one of the biggest bus systems in the world,

but it's also a bit of a mystery.

It's incredibly chaotic.

I have no idea what's happening.

But they're all going somewhere,

and all the locals seem to know which one to get.

These little buses are known as peseros.

They got their name because they used to charge one peso -

that's just 4p.

They account for an incredible 60%

of all journeys made by commuters every day.

But there are no bus stops and no marked routes.

How do you know? How do you know which one to get?

Peseros are an unofficial system that's grown with demand.

They're unregulated, unlicensed, and, crucially, unmapped.

I'm going to need some help to find my way.

-Hola, Christian.

-Hi.

-How are you doing?

VOICEOVER: Enterprising Mexicans like Christian Guerrero

are trying to bring order to the chaos.

So, how do you know what bus you need to get?

Well, mostly, you ask the people around.

Like, either your family or your friends.

So it's mostly, like, general knowledge in the population.

-Local, Mexican City knowledge?

-Exactly.

VOICEOVER: On average, Mexico City residents

spend about two-and-a-half hours a day commuting...

Thank you.

..much of it on buses like this.

And we're on.

How many peseros are there in Mexico City?

Around 50,000.

-Yeah.

-50,000 of these buses?

Yeah.

It's getting busy. Coming on, ladies.

VOICEOVER: Christian wants to modernise

the 40-year-old pesero system

and make it easier for passengers to use.

He's developed a smartphone app

that aims to map the entire network

with the help of passengers riding the routes.

The idea is that you would use your phone

in order to, first of all, take a picture

of the sign in the front of the bus,

and that picture would tell us which route it was.

So once you took the picture,

you would use your GPS and start mapping.

Do you know how many miles it covers?

52,000km.

So about 32,000 miles.

-Yeah. Exactly.

-That's a lot.

And it's an ongoing process.

Yeah, it's growing and growing.

It's a very smart solution -

crowd-sourcing routes so they can be made available

to anyone with a smartphone.

This is a fusion of the old and the new.

In 40, 50 years, nobody has done anything

in order to let this system work correctly,

so if we don't do anything, this city will stop moving.

And you're having to come up with apps and solutions to improve it,

-to bring into the 21st century.

-Yeah.

The peseros are an integral part of Mexico City.

They're typical of this place -

an informal and slightly haphazard solution to an urban problem.

Where else can you be serenaded while waiting for the bus home?

I love Mexico.

Standing on the side of a dual carriageway,

these chaps get off and start serenading me.

Yes, gentlemen. Muchas gracias.

-Have a nice evening.

-Thank you so much.

That was so wonderful, they were actually really good.

Now which of these peseros do I get home?

Do I get this one?

I have no idea. No idea.

Don't know where I am.

While Anita gets lost on the buses,

I'm off to discover what made this city great in the first place.

This is one of the oldest continuously inhabited settlements

in the Western Hemisphere.

The modern city might be an assault on the senses,

but you don't have to go far to see its ancient roots.

Everything here in Mexico City is a product of its unique past,

and there are places within the city where the past and the modern

are all jumbled in right next to each other.

Like here, modern apartment blocks, big, busy motorway,

but right next to it is this astonishing historical site -

the Place of the Three Cultures.

And those three cultures are, in the middle, the remains

of an old step pyramid from the Aztec period -

the Aztecs, one of the great civilisations of world history.

Then the Spanish arrived in the 16th century,

they literally dismantled those temples

and built churches like that right on top of them.

What a statement of colonial control.

And then there's modern buildings

from Mexico's post-independence period as well.

The Aztecs settled here because there was water.

They built their capital, Tenochtitlan,

on a small island in the Lake of Texcoco.

When the Spaniards arrived, they destroyed the island city

and started to drain the lake.

Where once was water, there's now sprawl.

But there's one corner of this modern megacity

where you can truly experience its history,

and it's worth getting up early for.

I've come now to the most beautiful place,

a very far cry from the noise and bustle of Mexico City.

The mist is coming off the water

and the farmers are working the fields.

It's beautiful.

This is Xochimilco.

Not far from the heart of the modern city,

this working landscape is an insight into Mexico City's watery past.

Early settlers built this ingenious system.

Artificial islands, known as chinampas,

on which to grow their crops.

-VOICEOVER:

-Lucio Usobiaga works with the farmers here

to try and preserve the islands and their way of life.

Did this used to extend right across the valley

that Mexico City now sits in?

Are we looking at the last remnants of these islands?

Yeah, we are.

In Mexico City, you know it's a basin,

so it had five lakes.

Right now, this is the last lake that we can really look at,

and that it survives with some of its traditions.

So this is the only place where you can come and get a feel

for what life was like under the Aztecs?

Yeah. Yeah, exactly.

These chinampas were all made for agriculture.

So they're all man-made?

All man-made, yeah,

more than a thousand years ago,

even before the Aztecs came here and conquered the xochimilcas.

Today, the chinampas are farmed as they've been for centuries,

growing crops like maize, tomatoes and chilli peppers.

This is lettuce.

-VOICEOVER:

-Lucio is taking me to meet

a fourth-generation chinampero, Noe Coquis.

Today, he's planting radishes.

Noe, are your kids doing this farming as well?

Is another generation of farmers being made?

There'll be people farming here for generations to come.

I really admire Noe's efforts

to preserve the ancient farming methods.

But Lucio wants to show me how these chinampas are being threatened

by the rapidly sprawling city.

We've come into a part of the chinampas now

where we're seeing more houses.

This one here built right onto the edge of the river bank.

We can see illegal houses.

It is not permitted to build houses in this natural protected area,

but because of the housing demand,

some people have no other alternative but to build them here.

But this sums up the development of Mexico City over the centuries -

people just constantly looking for new grounds,

people moving here from elsewhere.

There's a density of population here

which means people need to find new ground to build.

So do you think, if we come back here in 20 years' time,

the chinampas may not be here?

Well, I am hoping that there will be enough efforts and resources

to prevent this from happening,

and instead of seeing more houses, we'll start to plant more chinampas.

Let's hope so.

Mexico City was founded on water.

The great irony is that, today, it now faces a water crisis.

The draining of the lake system has left the city thirsty.

It uses more water every day than any other city in the world.

Millions are forced to get their water from trucks

known as pipas, because they can't rely on the mains.

I've come to a pipa depot in the borough of Tlalpan

that sends out 200 trucks a day.

It's pouring with rain,

these trucks are filling up with gallons and gallons of water

that's been piped down from the mountains,

and they're going to be taken by these trucks

back up to the mountains to be sold to the people.

It's just crazy.

Me llamo Ade.

-VOICEOVER:

-Uriel Canalez has been delivering water

across the city for a few years.

I'm amazed at what a precious and high-risk commodity

water is in this city.

Especially in the poorer neighbourhoods

on the very edges of the sprawl.

-VOICEOVER:

-I've come to meet Rogelio Ramirez and his wife Sofia.

They live in an area where water tankers are essential.

I'm really surprised at the drastic measures

that Rogelio has to take just to get the water that his family needs.

Uh-huh.

Yeah, it's just starting to rain.

It's getting a little bit heavier and it's a good sign.

This untreated water will be stored in a tank.

The family won't drink it, but they do put it to good use.

Wow, wow.

Not a single drop of water is wasted.

Families here can spend as much as 20% of their income on water.

It's not that it doesn't rain here - it's just most of it is wasted.

-VOICEOVER:

-Enrique Lomnitz is working to find

an affordable solution for everyone.

These are, kind of, the forgotten people

of the water situation in Mexico.

Even though we're talking about millions of people.

But that's crazy, when you get so much water in this area

and you're in a city that has problems with water,

why not use it?

That's what we said.

So we were like...

It seemed to us like it was just a really obvious thing to do.

So harvesting rainwater involves channelling the water

that falls on your roof, with gutters or whatever,

and putting it through some kind of treatment, and storing it.

-VOICEOVER:

-Enrique has been helping to install water capture systems

in Tlalpan for the past seven years.

Hola, hola.

-VOICEOVER:

-He's taken me to meet Eusebia Ventura.

Like most of the people living on the edge of Mexico City,

she has built her own home.

So this is a 5,000-litre tank, and we put, as part of the project,

the tank that's inside,

and as she's grown the house, she's connected more roof,

so now she has three rainwater harvesting systems.

I'm pleased to hear that this system is already saving Eusebia money.

So she makes something like 1,000 pesos a month

and it would cost her 800 pesos to fill this.

Whoa, here we go.

Eusebia now captures and filters

70,000 litres of rainwater every year.

I want to taste the water from the sky.

-Well, it looks clear.

-Yep.

-That looks clean to me.

Yeah.

So here's a glass of pure rainwater.

Yes.

And, you know, clean water in these areas is scarce

and becoming a more scarce resource, no?

-So it's like gold dust.

-Yeah.

It's perfectly clean water.

Muy bien.

Gracias.

It's fantastic.

-Si?

-I'm so impressed.

I am.

Getting water into this megacity is one problem,

but getting rid of it is quite another.

I've come to Ecatepec to see a system

that deals with one of Mexico City's dirtiest secrets.

This is known as "agua negra" or black water.

It's sewage waste water.

And these days, it flows through a largely open sewer

called the Grand Canal.

VOICEOVER: Today, Carlos Teran and his team

are cleaning the filters that keep the sewage flowing.

I have no idea what pressing this button will dredge up.

SHE EXCLAIMS

Holy crap!

It's a sofa.

I mean, this is horrific.

There's a whole dashboard here.

Yeah. I mean, it's horrendous,

but a vital part of any city, waste management.

It's grim,

but this is the reality of humans.

That poor guy.

This is one of 94 pumping stations

along 7,000 miles of tunnels and pipes

that form Mexico City's sewage system.

The Grand Canal is now more than 100 years old.

It used to flow downhill,

using gravity to carry waste out of the city for treatment.

But when Mexico City was drained,

the clay lake bed started to collapse,

forcing the canal up, not down.

Engineers now battle gravity to pump the agua negra uphill,

using pumping stations like this one.

Parts of the city have sunk an astonishing 40 feet

in the last century.

These pumps have to work hard.

So, Carlos, this is crucial, this is a crucial point.

So if this didn't work, within three hours,

the city would start to flood.

The pumps are just a sticking plaster

on Mexico City's sewage crisis.

The Grand Canal was not designed to deal

with the waste produced by nearly 22 million people

in an ever-expanding megalopolis.

So Mexico City is building big to solve its problem.

This is the Emisor Oriente.

It's an immense new waste water tunnel.

What they're doing now is lowering the outer rings of the tunnel...

..and each one of those weighs five tonnes,

and it takes eight of them to build the entire outer wall,

so that's 40 tonnes.

This is serious engineering.

This is it, we are descending 110 metres.

And this lift is actually going a lot faster

than I thought it would.

This is like the journey to the centre of the Earth.

Incredible!

It's like we've entered the underworld.

It's a lot darker, a lot cooler and there's a whole system at play here.

Hola, Jose.

-Hola, Anita.

-Yes.

VOICEOVER: Jose Lee Espinoza is the engineer in charge of this,

one of Mexico City's biggest engineering projects.

That was quite a descent.

-Yes.

-We are very, very deep...

-Yes.

-..in this enormous tunnel.

How many miles long is it going to be?

More or less, 64km from Mexico City to the treatment plant.

This is going to be one of the biggest tunnels in the world

-when it's finished.

-Yes, yes, I think so.

We're making our way towards the front of the tunnel,

where they're still drilling through solid rock.

All of Mexico City's sewage and overflow of rainwater

will be gushing through this enormous tunnel

right where we are now.

That's quite a thought!

This new tunnel won't sink like the Grand Canal,

because it's drilled so deep through hard rock.

In fact, it will actually help Mexico City's sinking problem

by stabilising the groundwater beneath the city.

Finally, we reach the very front of the tunnel,

as close as we can get to the huge drill

that's boring the hole.

The drill is just up ahead of us,

it's nine metres in diameter

and it's crunching away at the earth,

getting rid of all those rocks.

And as they're making space,

they're laying those big chunks of concrete

that go towards making the tunnel.

How many kilometres are left to finish the whole tunnel?

-4km.

-4km left to do?

-Yes.

-And that will take how long?

-Ten months.

-In ten months,

Mexico City will have its new massive sewage pipe.

Yes.

The more time you spend in this city,

the more you realise how amazingly it fights Nature at every turn.

Look at this extraordinary buildings here.

Over the years, it's slowly subsiding at different speeds

because the Spanish messed about with this place so much.

They pumped out the groundwater, they reclaimed land for building,

and, as a result, it's on very uncertain foundations.

Check out that one there - that is leaning quite heavily over.

It's all a bit haphazard.

This subsidence has damaged the water and sewerage system.

And it has another potentially deadly cost.

Draining the lakes has dangerously changed the geology of Mexico City,

leaving it vulnerable to earthquakes.

Some of the most important parts

of one of the biggest cities in the world

now sit on a quivering pile of mud.

The city is actually 200 miles from the nearest fault line

off the Pacific coast,

but the drained lake bed acts as an amplifier -

seismic waves ripple and build as if shaking a bowl of jelly.

Most cities have emergency services -

police, ambulance and fire - but if you live here,

you also need a 24-hour specialist search and rescue team...

..like this elite unit.

They're part of the Mexico City Police Force.

They train every week, and today, they've agreed to show me

how it's done.

This is it. My childhood dream's come true.

I'm going to get to pretend I'm a policeman for a minute.

OK. Ready.

Yeah.

Right. Good.

-VOICEOVER:

-After an earthquake hits,

it's critical to get victims out of collapsed buildings

as quickly as possible.

The team use drills to create a weak point in the wall,

but then it's down to sheer brute force.

That is exhausting. OK.

-VOICEOVER:

-I think it's time to hand over to a professional.

Nice.

That does give you a little bit of a sense

of what it is like doing search and rescue in a huge city

where you may have to do that time and time again,

there's no end to the amount of buildings

that could collapse, trapping people.

The residents of the city have good reason to be fearful of earthquakes.

In the early hours of the 19th of September 1985,

Mexico City was devastated by a massive 8.1 magnitude earthquake.

In just over a minute, around 100,000 houses were destroyed

and 5 million residents were left without electricity

or drinking water.

Around 10,000 people were killed.

It's very clear that the 1985 earthquake

cast a long shadow.

They don't want that to happen again, they're not going to let

their fellow citizens suffer like that again,

so they've got the tools, they've got the training,

and they've got the techniques.

I'm not sure I'd cut it on their team.

Rescue teams are Mexico City's last line of defence.

But that's not all.

In a city where millions live in self-built houses,

they've also developed

the most effective early warning system in the world.

It buys people crucial time to evacuate.

I've come to the National Seismological Service

at Unam, the National Autonomous University of Mexico,

to meet Dr Xyoli Perez-Campos.

How far down are we going?

We are going to go 20 metres down.

20 metres, OK.

At the bottom of this shaft are highly advanced seismic sensors.

These are the latest technology

and the most precise instrument in the world.

They're part of a network of more than 150 sensors

constantly monitoring the Earth for tremors.

Did this detect Haiti? Did it detect Pakistan?

Yes. Like Japan, 2011.

Isn't that amazing?

That something that's happening on the other side of the planet

can be detected here in Mexico City.

The tremors picked up by the sensors

are monitored right here at the University.

We report daily an average of 32 earthquakes per day.

Hang on a minute - 32 earthquakes every day on average?

-Yes, yes.

-That's a huge figure.

Most earthquakes are small tremors that few people notice.

But when a bigger quake strikes, the early warning system kicks in.

With the main fault line 200 miles away,

this technology gives more than a minute's warning

before the shock waves actually hit.

It's a system that saves lives.

So you'll have detected one today?

Yes - actually, this morning, we have a big one.

It had a magnitude of 5.6 and we can see the record on the screens.

It happens off the coast of the country,

so it was in the Pacific, so nobody felt it.

When do you think the next earthquake will hit here?

Well, today, we will have one, but a small one, of course.

We don't know if a big one is going to happen

or when it's going to happen.

The more we explore this city,

the more we're learning it works because it doesn't live in fear.

Its streets positively brim with life.

That optimism underpins big plans for the future.

The sprawl can't go on forever...

..so there's only one way to build,

and that's up.

But how do you build a skyscraper

on an unstable lakebed in an earthquake zone?

This is the Torre Reforma.

Standing 256 metres and 57 storeys high,

it's Mexico City's tallest building.

-Hello.

-Welcome.

-VOICEOVER:

-Its architect, Benjamin Romano,

is here to show me the secrets

behind this incredible feat of engineering.

Embedded in the concrete slab,

we have this connection that goes to the edges of the concrete wall,

so in the case of an earthquake,

these elements will control the building not to move

where the building doesn't want to move.

-So it lets it flex a bit, but not too far.

-Exactly.

In sinking the foundations of the skyscraper,

Benjamin needed to take into account the city's waterlogged past.

Those concrete walls are embedded 60 metres underneath the street.

-So you've gone below the lakebed, all the way down?

-Exactly.

So for us, the earthquake issue because of the lake means nothing.

Now that I've seen this, I'm feeling more confident

about going up Mexico City's tallest building.

I think, even if there's an earthquake, we're going to be fine.

-You are going to be perfectly safe.

-OK.

There are 28 lifts serving more than 4,000 people.

Everything in this cutting-edge building

is designed not only for looks, but also for safety.

So, Benjamin, these windows are a very unusual shape.

Yes. Since they have to behave in case of an earthquake,

these window needs to move 10cm.

The windows in this building

are designed to bend and flex during an earthquake

to release the build-up of pressure.

So this is like leaving a ready-made crack in the side of a building?

Yes, exactly. It's to allow the two different elements to move.

It's so strange talking about high-rise buildings moving,

because from the ground, they look so static and strong,

and here you are, telling me that they're always in movement.

They all have to move, because either for wind or seismic...

It's like if I push you -

they will move and come back to the natural.

This iconic building, now punctuating the skyline,

looks to the future of Mexico City.

It's earthquake resistant,

it has its own rain and waste water harvesting system,

and it even has robots that will park your car for you.

-VOICEOVER:

-On top of all that, it has quite a view.

I mean, I'm almost speechless at how big Mexico City is.

I mean, from up here, it just stretches...

-Well, it stretches as far as the eye can see.

-Yes.

Did you ever think you'd be responsible

for the tallest building in Mexico?

Never in my life.

It is a very unique feeling. So far, I'm very happy.

Standing here on top of the tallest building in Mexico City,

I'm in awe of what Benjamin and his team have achieved.

Their ingenuity has overcome so many hurdles

placed in their way by nature,

and if Mexico City represents a battle

between human habitation and nature,

this is a war-winning strategy.

Building for the future here doesn't stop at skyscrapers.

Getting 22 million people in and out of the crowded city every day

is a challenge, especially with its haphazard bus service.

But I've come to the suburb of Ecatepec

to discover that almost anything can be built

in this spirited city.

Well, wow, look at this -

it's just like everything else here in Mexico City,

a big surprise.

The last thing I was expecting to find here is a cable car.

It's accessible as well.

There's a wheelchair entrance, there's a ramp -

I'm loving it already.

The views from the Mexicable,

you've got this sprawling city and these murals

and the amazing colours on the houses.

It's just breathtaking.

This cable car system was only completed in 2016.

It costs just six pesos, or 26p, to ride,

and already, nearly 30,000 people are using it every day.

-VOICEOVER:

-Victor Jasso is the engineer

who keeps the system running smoothly.

So, Victor, why build it here and why build it now?

Because this area has a really big problem.

There's not too much roads, there are not so much highways,

so we have a lot of people living here,

so a cable car, it's totally a solution.

You don't have a stoplight, you don't have traffic.

So now they're more connected...

Yes, yes, that's the word, connected.

Can you tell me about the mechanics? What goes into this?

Cos it looks like an enormous engineering feat.

This cable car is moved by an engine.

The engine is the big red one over the station,

and with that engine, we move the whole loop

between station four to station one.

The one engine moves all of these cars across four stations?

-Yes.

-Wow.

There are seven cable car stations in total,

running just over three miles,

connecting some of the city's poorest

and most isolated hillside neighbourhoods.

The system is run from control rooms like this.

With this button, we can reduce the speed,

because sometimes, we have some people

that maybe need more assistance.

Actually, we've got a wheelchair customer,

do you need to slow it down?

Yeah. Just put it in lento uno.

-Speed...

-The speed reduces...

-So it makes it slower?

-Yeah.

-And this now allows this lady in a wheelchair to get in easier?

Yes.

-VOICEOVER:

-This technology is really unexpected.

It looks like it's quite easy for him to pull.

Yeah, and it's really, really easy for pushing.

You know, it's amazing, the cabin, it's one tonne.

So this is a tonne and we can just push it?

-Yeah.

-Wow, that is so easy!

Look at that, one finger. Look at that!

That's incredible.

That system is so smooth.

I need that for my wheels on my chair.

This all makes for a very different commute for local residents.

-Hola.

-Hola, buenos dias.

-Buenos dias.

-Como estas?

-VOICEOVER:

-Daniel Gimelo is a shoe shiner.

Every day, he travels on the cable car with his bike,

then cycles the rest of the way into the centre to find work.

It's morning rush hour and commuters like Daniel

are flooding onto the cable car to get to work.

But it doesn't just save them time.

Juan Martinez Jurado uses the cable car every day.

This new public transport system

hasn't just improved the commute for locals -

it's also transformed the surrounding neighbourhood.

It's incredible, it's almost like this Mexicable

has given this whole area a face-lift.

All of these images and paintings have just sprung up

because of the Mexicable.

And what it's done is it's just lifted the ambiance

of this whole area.

It's just made it really beautiful,

and it's such a nice way to get to work, I think.

There's a feeling all across Mexico City

that it's cleaning up its act.

And not a moment too soon,

because Mexico and its capital have a poor reputation for crime.

To find out how this city polices

a sprawl of almost 1,000 square miles,

I'm taking to the air.

Well, we're just about to take off, now, the aircraft is warming up.

We are going in the Mexico City police observation helicopter.

This is the key to making sure that a relatively small police force

is able to maintain law and order in this vast and complicated city.

It's using the eye in the sky, linked to the ground technology.

In Mexico City, there are almost 90,000 police officers.

Officer Carlos Moreno is a specialist camera operator

who works the skies in one of 13 helicopters.

How hard is it to keep order in a city of over 20 million people?

So difficult.

As you see, it's really big.

But we have excellent communication with ground units.

We got, also, all the time,

one helicopter flying around the city.

We can cross the city in five minutes.

With this technology, Carlos can home in on one target

in a city of millions.

I'm going to show you how we follow a car.

We can follow automatically.

I don't have to move anything.

That's clever, so you can track a target.

Once you lock onto it, yeah.

How much closer can you go?

Could you read the license plate on there?

We are going to try.

That's astonishing.

-Yeah.

-You can see right into the back of his vehicle.

Yeah, exactly.

-VOICEOVER:

-The police can track suspects

all the way across this huge city.

Down is down, up is up, left and right, it's the same.

-And you zoom in like this?

-And you're going to follow...

That's incredible.

I feel like I'm going to crash into that building!

Air units like this allow the police to stay one step ahead.

This is a sprawl that spreads as far as I can see in all directions.

It would take hundreds of thousands of policemen and women on the ground

to maintain control,

but, by using this, you can use those other resources

far more efficiently.

Technology like this is an essential ingredient

if these modern megacities are to be sustainable and safe.

While Dan avoids the traffic in the sky,

I'm in the thick of it on the ground.

Monday morning rush-hour traffic in Mexico City,

but it's not as bad as it normally is,

because the smog levels have been so high this week.

In fact, the highest smog levels recorded in the last 20 years.

HORN BLARES It's all happening here.

Get it into gear, mate.

And off he goes.

The smog levels are so high that the authorities take measures

to reduce the number of cars on the road,

so even though this looks insane,

it's not half as bad as it normally is.

But something is changing here.

Take a walk around the streets nearby

and the atmosphere becomes noticeably calmer.

Pimped.

This is Paseo de la Reforma,

a wide avenue running diagonally across the heart of Mexico City.

It's usually full of cars, but not today.

-Hola, Areli.

-Hola.

-Lovely to meet you.

VOICEOVER: Areli Carreon is a cycling enthusiast and campaigner.

She's also Mexico City's first-ever bike mayor.

I'm totally blown away by what's happening.

-Tell me, it's a Sunday morning.

-Yes.

-What is this?

Is this a one-off event?

No, it happens every Sunday,

and it's a close-down of a main street in Mexico City.

This is Reforma, one of the most historical

and most iconic streets in the city.

-This is like shutting down the Champs-Elysees.

-Yes.

There's, like, 50,000 people

and, as you can see, there's people from all walks of life here

enjoying the city.

-Somebody's listening to their music whilst they're cycling.

-Yeah.

Oh, it's not just a little bit, he's got a massive ghetto blaster.

Yeah. Look at that.

All of this cycling is yet another way

this massive megacity is cleaning up its act.

Mexico City has, like most major cities,

a real problem with pollution, doesn't it?

Yeah, of course. The average speed in the city on a car

is the same as bicycling, it's 15kmph, which is insane.

If we don't do something about this,

eventually, we wouldn't have enough clean air to breathe.

This city loves to live life on its streets.

That's amazing, look - he's got Grandma on the front,

baby on the back, maybe that's his grandson.

One of the things that I like the best

is it doesn't matter who you are, which is your walk of life,

people get to be together and enjoy

and have a conversation and just be around.

Well, I feel like you're telling me to get on this bike.

I feel like, subliminally, you're just like,

-"Anita, I've got you a bike."

-Let's go!

-"Get on."

-Shall we?

-Yes.

-I feel like we should join everybody.

Let's go.

Whee-hee!

Oh, it's great fun.

It's such a brilliant way to see the city as well.

What a great bit of progressive civic planning,

cos at the heart of every city are its people,

so let the people take over the streets.

On top of that, it's great fun.

BELL RINGS

Mexico City is full of surprises.

This is a city where cars are giving way to bicycles...

..where cutting-edge cable cars

glide over self-built neighbourhoods...

..where sprawl meets skyscrapers.

It may be fighting a daily battle with Nature,

but it's a fight that its enterprising, optimistic

and resilient citizens are determined to win.

Next time...we're in Moscow...

Muscovites everywhere.

..exploring a city forged by power and politics,

that plays by its own rules.

I've never been allowed inside the red walls of the Kremlin before.

Uncovering the systems and traditions...

Are you on time?

Honestly, I'm three hours late.

..that make this one of the world's busiest cities.