Original subtitles

The magnificent Aztec Empire -

one of the most powerful civilisations the world

has ever seen.

The Aztecs were fearsome, they were clever,

they were a force to be reckoned with.

700 years ago, the Aztecs dominated Mexico.

They were ruthless warriors and ingenious engineers.

But after just 200 years,

their vast empire was wiped out by Spanish invaders.

They would never have seen metal weapons,

they'd never seen guns before.

It was like wielding lightning or thunder.

For centuries, archaeologists have been trying to understand

who the Aztecs were, and how they built their remarkable empire.

Can a series of new investigations,

and a ground-breaking experiment, help solve these mysteries?

Our cameras have been granted unique access to follow

investigators as they venture inside rarely seen ancient sites.

From brand-new excavations that reveal astonishing secrets

about how the Aztecs lived, and died...

IN SPANISH:

..to spectacular drawings that may explain

the truth about their origins.

IN SPANISH:

Will these extraordinary clues,

and a pioneering attempt to build a real Aztec pyramid...

If we get this wrong, there is a high likelihood

that our pyramid could collapse.

..shine a light on the incredible secrets of the Aztecs,

and reveal what life was like inside one of the greatest

empires in history?

Mexico City -

one of the world's largest,

home to more than 21 million people.

From beneath these modern streets,

an astonishing hidden world emerges -

the capital of the Aztec Empire, Tenochtitlan.

In the 15th century this was the largest city in the Americas

and one of the biggest on Earth.

At its centre was a great pyramid, Templo Mayor.

Now it lies in ruins, but it was once the heart of the Aztec world.

The Templo Mayor was constructed by the Aztecs

as the cosmic centre of their universe.

Absolutely everything relating to religious life,

political life in the Aztec empire all came down to this central point.

Archaeologist David Walton has been studying the Aztecs for ten years.

He wants to investigate who they were,

and how they were able to build these stunning monuments.

600 years ago, this was a brightly-coloured pyramid,

towering over 60-metres high.

One of the most magnificent temples in the Americas, Templo Mayor

was the centre of a huge sacred complex,

the seat of power of the Aztec Empire.

Around it, the Aztecs built their capital city, Tenochtitlan.

Sitting on an island in the middle of a lake,

this sprawl of houses, canals and causeways

covered 13 square kilometres and housed up to 200,000 people.

So many people think about the Aztecs as this primitive,

brutal society,

but what's so impressive about them are the engineering skills

that they had, the ingenuity, the tenacity that they had

to build such a great empire in such an inhospitable location.

In the 15th century, the Aztec Empire dominated the region

now called Mexico.

It covered an area the size of Great Britain

and was home to up to 15 million people.

But why did the Aztecs decide to build their capital city

on an island in the middle of a lake?

And how were they able to build extraordinary structures

like Templo Mayor?

Building a city on marshy ground would have presented

an incredible challenge.

So it's so impressive that it's still standing.

This was not done by a primitive society.

In the heart of Aztec country outside Mexico City,

David searches for answers.

He wants to understand the secrets behind how the Aztecs

built their incredible pyramids.

The fact that Aztec structures are beneath modern Mexico City

means that we really don't know how the Aztecs actually

built their pyramids.

David plans to undertake an ambitious experiment, to investigate

how the Aztecs constructed great monuments like Templo Mayor.

He's gearing up to build a modern-day replica Aztec pyramid.

Hey, Lucas. Hello, David. How are you?

How are you doing?

David works with Mexican architect Lucas Cantu.

Together, they're attempting something that hasn't been

done for centuries.

The Aztec culture,

it's very interlocked with Mexican history, but, in a way,

it's also very mysterious because what we know now,

it's about going to archaeological sites

and archaeological sites are in a ruined state,

so we actually don't know much and a lot of it is just hypothesis

and imagining what was it like.

The Aztecs had no metal tools or wheeled vehicles.

There were no horses in the Americas at the time.

To find out how they managed,

David and Lucas plan to use as many traditional tools

and techniques as possible, to build their own Aztec pyramid.

So, in a way, we're going to keep it very raw,

but obviously it's going to be a little bit more bumpier.

Got it, OK. So...

Their plan is to build a scale model, five-metres square

and two-metres tall, with three tiers.

We think we're going to have big challenges

just by building this, because we've never actually done it,

so we're going to have a lot of setbacks

just by trying to work around with the tools

we're not used to working with.

There are so many things we don't know.

This isn't like building a house.

I've never done this before, Lucas has never done this before.

I mean, we're just trying to figure it out.

Before they can start, they need to understand more about

who the Aztecs were and where they came from.

In Mexico City there's an ancient document

that's so precious, almost no-one is allowed to see it.

It's known as the Boturini Codex.

Library Director Baltazar Brito

decodes a reproduction to search for clues

about the origins of the Aztec people.

IN SPANISH:

The Aztecs didn't have an alphabet.

Instead, they used images to record every detail of their lives.

Baltazar believes the codex was made in the early 16th century,

just before the fall of the Aztec Empire.

He wants to see if it will tell him where they came from.

In search of a new home,

the Aztecs travelled across Mexico for 200 years.

Eventually, they arrived in a valley

with a lake rich in bird life and fish -

Lake Texcoco.

On an island in the lake they saw an eagle landing on a cactus...

EAGLE SCREECHES ..with a snake in its beak.

They believed this was a sign from the gods.

In this sacred place they founded a new city

and called it Tenochtitlan - "the place of the cactus rock."

On the spot where they saw this supernatural message,

the Aztecs built the towering Templo Mayor.

It's just one of thousands of pyramids

and temples the Aztecs built across their empire.

Many are still standing today.

13km north of Templo Mayor is Tenayuca.

It's home to the best-preserved pyramid in the Aztec world.

Archaeologist Beatriz Zuniga investigates how it was constructed.

IN SPANISH:

But what kind of stone is the pyramid made of?

Beatriz takes a closer look.

Thanks to the region's volcanic past, the Aztecs were

surrounded by a ready supply of different types of volcanic stone.

The main material they used for Templo Mayor is called Tezontle.

At Tenayuca, the Aztecs used the local volcanic stone

to construct a pyramid 30 metres high and over 60 metres long.

Sourcing and cutting all this rock by hand

would have been an epic task.

Using manpower alone, the Aztecs created magnificent pyramids

to awe and inspire their people.

How did they extract so much stone without metal tools?

At this quarry outside Mexico City,

archaeologist David Walton investigates how the Aztecs

cut the blocks they needed for their monumental structures.

Hey, Alejandro.

Good to see you.

He works with Aztec expert Alejandro Pastrana to cut

a stone like the ones at Templo Mayor.

The main material the Aztecs used was a volcanic rock called Tezontle.

It's still one of the most popular stones

in the Mexican construction industry.

At this quarry they extract red tezontle.

The rusty colour comes from its high iron content.

The Aztecs exploited places like this

to get the stone for their pyramids.

David wants to cut a block that's a similar size to the ones

used in the pyramids of Templo Mayor and Tenayuca.

But how did the Aztecs manage to quarry

such large quantities of stone

without the help of metal tools and machines?

Historian Caroline Dodds Pennock

has been studying

the Aztecs for more than two decades.

She investigates another ancient codex.

She believes it holds the key to understanding how the Aztecs

got the stone to build their magnificent pyramids.

The Florentine Codex was

compiled in the 16th century by a Franciscan friar.

It has over 2,000 beautiful illustrations which were

drawn by indigenous artists,

and it also has Spanish and indigenous language text,

describing indigenous culture, society

and the conquest in 12 books.

The codex runs to a staggering 2,400 pages,

covering every aspect of Aztec life.

It's probably the most valuable source of information

on the Aztecs in the world.

The manuscript is so precious that, actually,

I've never seen it in person.

It's kept in temperature-controlled conditions in Florence.

That's why it's called the Florentine Codex.

And it is so important and valuable as an artefact

for the history of Aztec culture

that we just aren't allowed to touch it.

The 12 books of the codex cover everything from religion

and society to the conquest.

The pages Caroline wants to examine

are the ones that deal with daily life.

They explain all the different jobs that people do,

from priests to farmers and, of course, stonemasons.

This is a wonderful illustration of Aztec stone-working,

from the beginning of the process to the end.

You have people in the background quarrying the stone, and then people

splitting it into manageable blocks.

There's a chap here with a stone axe with a wooden handle,

and then right down at the front people with

chisels and, again, stone hammers

to split the stone and work the stone.

Workers did this hard labour all year round,

even in the heat of summer.

Just how difficult a job is this?

At the quarry, David and Alejandro

gear up to cut the block they need for the pyramid.

They work with stone tools modelled on the ones shown in the codex.

All right, ready to go? OK. Let's go.

Alejandro has found a piece of tezontle that he thinks is

the right hardness.

IN SPANISH:

OK, so we need to go all the way around here,

start cutting into it that way, and then come down over there.

Okay, just try to... Yes.

Aztec tools were usually made of hard stones, like basalt or flint.

Stone masons use the harder rocks to bash away at the softer tezontle,

chipping off a little at a time.

But the tools are no easy to work with.

Oh! Oh, man, look at that.

So this was like a constant repair of these tools,

let alone the hours that it takes to actually

take a block out from the tezontle.

Labourers spent months cutting thousands of stones by hand.

It's difficult and dangerous work.

Oh! Oh, man, yeah, I cut my hand right here.

So, yeah, we're talking about blisters,

cuts on people's hands.

This is a really, really kind of hard task for people to do.

Aztec stonemasons had years of practice and experience,

but for David and Alejandro it seems like an impossible job.

If they're going to get even one block cut in time,

they'll need help.

IN SPANISH:

Help has arrived!

Ciro works at the quarry.

He's an expert in cutting stone by hand.

He switches to metal tools to get the task done.

Here, let me try and give it a go.

Oh, man, this is heavy! HE LAUGHS

Even with modern equipment, it's still a tough job.

Ooh!

OK.

It's taken them four hours of backbreaking work,

but, eventually, the stone is free.

Yes!

That's awesome.

All right! Good job. Good job.

It would take thousands more stones like this to make a full

pyramid the size of Templo Mayor.

Oh, yeah. Oh, perfect.

Yeah!

While Ciro breaks the stone into portable pieces,

David wants to find out more about Aztec tools.

The Aztecs didn't have metal,

so what kind of material did they use for tools to cut things?

Obsidian?

Obsidian is a volcanic glass.

It forms during an eruption, when lava cools rapidly.

The area around Mexico City is a major source of obsidian.

But how do you make a tool out of glass?

OK, so you're going to hit this core with this hammerstone

and we're going to get a tool out of what you're using right there.

OK.

Alejandro needs to try to chip off a piece without it shattering.

But will the new tool be sharp enough?

Yeah, OK.

What? That is super sharp!

The razor-sharp obsidian slices the leather like a knife through butter.

That is magic, yeah.

That's incredible.

In fact, it's better than a knife.

OK, I'll try a steel knife.

What?

Look at that.

I'm really... That's not... HE LAUGHS

The Aztecs thought obsidian was created by the gods

when lightning struck the earth.

It was so precious, they even used it as a religious offering.

Would say this is one of the most important materials or the Aztecs?

Okay.

Okay.

It's almost like a surgeon's tool.

It's that sharp.

Once Ciro has finished breaking up the block, the team faces

the next challenge that the Aztecs would have encountered.

How did they transport all their heavy building material

to the pyramid site?

A tumpline is a woven strap attached to a bag or basket.

OK. Yes. Got it. So we put all the stones in here,

and then how does this work?

Like, where does this part go?

On your head? Ah! Wow.

Many traditional societies still use tumplines today.

The Aztecs made theirs from the leaves of the agave plant.

OK. So, how do we get the fibre out?

Alejandro uses his obsidian blade to cut the leaf.

The super-sharp volcanic glass slices through easily.

Oh, wow, I can see it, yeah.

Oh, there it is, yeah.

Ah! Got it.

Oh, OK, twist it up to make cord.

The Aztecs used agave fibres for weaving ropes, cloth,

and baskets like these tumplines.

So, this is the tool,

this is what we need to get our stones to the pyramid.

All right, let's go. Let's go try and do this.

The Aztecs needed thousands of porters to transport

items from place to place.

They made up the largest sector of the Aztec workforce.

All right. Yeah, that's pretty heavy.

I think I'm ready. Yeah? Yeah. All right, let's go.

An Aztec porter would have had to carry at least 40 kilos

of goods or stone on foot, walking for days over rough terrain.

All right, just about 25 miles to go.

It's backbreaking work.

Why did the Aztecs go to

so much trouble to build their enormous monuments?

What were the pyramids for?

The answer may lie at this incredible ancient complex

almost 50km northeast of Templo Mayor.

The site is called Teotihuacan.

It's over 1,000 years older than any Aztec pyramid.

Sergio Gomez has been working here for over 30 years.

He investigates if there might be a link

between this stunning city and the Aztecs.

IN SPANISH:

Teotihuacan is home to three main pyramids,

and more than two dozen smaller structures.

The biggest is the Pyramid of the Sun.

It's the third largest pyramid in the world,

towering over 70 metres high.

But 700 years before the Aztecs founded their empire,

this remarkable civilisation mysteriously collapsed.

Sergio believes there's a link between this eerie ghost city

and the Aztec people seven centuries later.

Stunning objects found nearby could provide a clue.

These extraordinary objects were found right here

in Teotihuacan.

But the designs aren't local.

So who made them?

Finding Aztec objects at Teotihuacan is an astonishing breakthrough.

It proves that the Aztecs came here.

The Aztecs thought these incredible structures

could only have been built by the gods.

They believed Teotihuacan was the centre of all creation.

Inspired by pyramid-builders before them,

they built their own monuments like the ones they saw here.

Sergio wonders if these pyramids might have a similar purpose

to the ones in Egypt.

The pharaohs of Egypt built their pyramids as elaborate tombs.

Each pyramid contains a hidden chamber where the pharaoh was

laid to rest.

Are the Mexican pyramids the same?

Searching for answers,

Sergio investigates one of the main monuments.

A mysterious entrance leads deep underneath the temple.

Sergio was the first person to set foot inside.

This claustrophobic passage way

has lain undisturbed for nearly two millennia.

It leads more than 100 metres directly underneath

the Temple of the Feathered Serpent.

What is this place, and why was it built?

Sergio and his team removed more than 1,300 tonnes of soil and debris

to find out what lay behind.

At the end of the tunnel, the team found a spacious chamber.

Inside were four greenstone figurines

arranged to face the centre of the temple above.

The floor around them was once a sculpted landscape

of jagged mountains and deep valleys flowing with pools of mercury.

On the ceiling, a glittering layer of powdered fool's gold

created the illusion of a starry night sky.

What was this strange landscape,

hidden right under the Temple of the Feathered Serpent?

Sergio believes this was a sacred ritual space.

But is it a tomb, as Sergio predicted?

Further discoveries inside the chamber provide a clue.

These stunning treasures appear to be the grave goods

of a rich and important person.

The landscape represents the underworld,

where he will reside for all eternity.

But if this is a tomb...

..where is the body?

Sergio believes the king's body was probably disposed of

by a rival ruler.

But the objects suggest this eerie underworld beneath the temple

is indeed a tomb, just as he predicted.

So were Aztec pyramids also used as tombs?

No traces of burials have been found inside Aztec pyramids.

They were places of worship, not graves.

The most important, Templo Mayor,

sat at the heart of a huge sacred complex designed to honour the gods.

But this holy place was built on an island

in the middle of a lake.

What can its challenging location

reveal about the Aztecs' engineering skills?

At Templo Mayor, archaeologist David Walton investigates.

When you look down here at the Templo Mayor,

you can get a sense of how much work was invested here

to make this temple.

It must have taken so much central planning and organisation

to put something like this on such an undesirable spot.

The city of Tenochtitlan was home to 200,000 residents.

With so many inhabitants,

keeping people and goods moving was vital.

Tenochtitlan was the heart of the Aztec empire,

so it was absolutely crucial

to have an effective transportation system

bringing things in and out.

The Aztecs used their engineering know-how

to create a sophisticated city layout.

The island where the Aztecs founded their city was 5km across.

Here, they built the ceremonial centre

with the Templo Mayor at its heart.

But as the population grew,

Tenochtitlan had to expand, and spread out into the lake.

Canals and dirt roads ran through the reclaimed land,

and canoes were the main means of transport.

To reach the lakeshore,

the Aztecs built three huge causeways up to 11km long,

creating a city the Spanish later called

the "Venice of the New World".

The Aztecs constructed a pioneering transport system,

which allowed them to bring the goods they needed

to the city centre.

This revolutionary town planning can still be seen in Mexico City today.

Even though the Aztec Empire is gone today,

modern Mexico City is built on the layouts

that the Aztec put here for their capital.

Some of the major streets in Mexico City

run right along the major causeways

that were there at Tenochtitlan when the Aztecs were in control.

Tenochtitlan has been destroyed,

but much of Templo Mayor is still standing.

How is this possible?

David heads into Mexico City centre to investigate.

He's on a mission to build a pyramid using Aztec methods.

But building in Mexico City poses a unique challenge.

Over 700 years ago, when the Aztec first came here,

it was an island in a huge lake.

So, when they had to figure out

how to build all of the pyramids and sculptures and big monuments,

they had to figure out how to deal with the soft ground.

Mexico City is no longer a lake.

After the Spanish took over in the 16th century,

they drained the water and built the city over the top.

All these buildings are sitting on what used to be the lakebed.

It's causing huge problems.

We can see some stones up on the walls are straight,

and some of them are kind of curving like this.

And if we look at the sidewalk, you can see the same type of thing.

That's the building sinking down into the ancient lakebed.

In many areas, the ground is soft and unstable.

Parts of Mexico City are sinking up to a metre every year.

There are buildings just like this all over Mexico City,

that are crooked and sinking down, and that's a problem to figure out.

David needs to make sure his pyramid doesn't suffer the same fate

as these collapsing buildings.

But how?

A clue may lie beneath one of Mexico's most famous landmarks.

This monument behind me is Mexico's angel of Independence.

And when it was originally constructed in 1910 it had 9 steps.

But, if you look, see here today, it's got some scaffolding around it.

But there's 26 steps that are there now.

So that means they had to add 17 over time.

And that's because the surrounding landscape

is all sinking down about 3 metres.

David takes a closer look.

He wants to know why this monument

is not sinking when the land around it is.

The answer is hidden behind the scaffolding.

So it turns out the secret is that this monument

has really strong concrete piling foundations

that's helping to anchor the monument in place.

While the rest of the area doesn't have those foundations

and it's sinking.

Evidence uncovered at Temple Mayor

suggests this was a strategy the Aztecs knew well.

Here, archaeologists have unearthed wooden pilings

driven deep into the ground.

They supported the monuments and ensured they didn't sink.

With it's concrete pilling foundations

the Angel is able to stay in place.

That's the key - it's all about the foundation.

To build a pyramid, the Aztecs first rammed wooden poles into the earth,

and made walls of hand-cut stone and mortar around these foundations.

To construct the first tier,

they poured in tonnes of rubble and earth.

Then they repeated the process to build a small pyramid.

As their power grew, they built bigger pyramids over the top

to create stone giants, like Templo Mayor.

The Aztecs constructed 78 monuments in the heart of Tenochtitlan,

covering an area the size of 22 football pitches.

Armed with this information,

David's team begin work on their pyramid.

They use pilings made of wood to replicate the Aztec techniques.

This area of Central Mexico was once dominated

by a very, very dense forest with pine, oak and cypress trees.

And what the Aztecs probably did was use probably pine or oak

for their foundational pilings.

The team estimates the pyramid will weigh at least 20 tonnes.

They calculate how many pilings they need to support it.

They decide to use a grid of 25 stakes, spaced 80cm apart.

This may be the most important decision of the entire build.

If we get this wrong,

if we don't place our pilings in the right place,

there is a high likelihood that our pyramid could collapse.

The team must also make sure the pillings

are properly sunk into the ground

so they'll sort the weight of the pyramid.

But digging with traditional wooden tools isn't easy.

So, we're finding it hard to do it,

and it's taking too long.

We've broken a few pieces.

Lucas is amazed at just how strong and dedicated the Aztecs were.

I don't think we're going to be able to dig 25 holes

with wood stakes,

so I think we're going to have to change and just use metal rebars.

Even with metal tools,

it takes the team an entire day to install all the pilings.

Now Lucas needs to make sure they're strong enough

to support the pyramid.

So, right now they're wobbly,

but actually, when we fill the core in,

they're going to get stronger,

so everything is going to get tighter as it gets filled up.

The only way to find out if they've got the foundations right

is to start building.

But why did the Aztecs need such impressive pyramids?

At Tenayuca,

13 kilometres north of Templo Mayor,

Beatriz Zuniga is on a hunt to find out more about the pyramids.

This is the oldest and best preserved pyramid in Mexico today.

These temples were the most important part of the monument.

Can carvings at the base of the pyramid

reveal who they were built for.

In Aztec mythology,

Xiuhcoatl, the fire serpent, belongs to the god of war,

Huitzilopochtli

He was one of two gods worshipped here.

hAztec historian Caroline Dodds Pennock investigates

clues in the pages of an ancient codex.

This stunning manuscript is a detailed account

of life in the Aztec world.

This is an image of a priest dressed as Tlaloc, the water god,

god of fertility and rain.

You can tell it's Tlaloc

because he's got his heron feather headdress,

he's holding a shield with a water flower on it,

and he has a reed staff.

One of Tlaloc's main roles was to send rain

to nourish the growing crops.

It was crucial for the Aztecs to worship him,

to ensure the success of the next harvest.

The codex also provides information

about the Aztecs' chief god, Huitzilopochtli.

Huitzilopochtli is god of war, he is the god of the sun,

and he's the tribal god of the Aztecs.

Here in the picture, he is wearing hummingbird feathers

because of his name,

which means something like "hummingbird from the south".

And he's also holding a snake staff.

The snake staff is the Xiuhcoatl, the fire serpent,

and that's an association with the sun.

As god of the sun,

Huitzilopochtli makes the sun rise each day.

Performing rituals to him will ensure that this happens.

As god of war, he's also responsible for the Aztecs' military success.

War is enormously important to Aztec culture,

because warfare is one of the central ways

in which their city sustains itself.

They have to go to war or threaten people with war

in order to bring in the goods and the food

which allow this city on an island to succeed.

But there's another reason why Huitzilopochtli was so important.

According to legend, his mother was a goddess

who wore a skirt of snakes,

and had 400 sons and one daughter.

When she became pregnant

with Huitzilopochtli,

they plotted to kill her.

But Huitzilopochtli was born fully armed,

and slaughtered his brothers,

who turned into the stars in the sky.

Then he ripped his sister apart,

and when he threw her from the sacred mountain,

she turned into the moon.

Huitzilopochtli himself transformed into the sun,

the all-powerful creator.

This myth is incredibly important in Aztec society

because Huitzilopochtli, as well as being the sun god,

is the tribal god.

He symbolises Aztec society, he symbolises Tenochtitlan itself.

And the myth symbolises the Aztecs triumphing

over the first threat to their power and influence.

At sacred pyramid sites like Templo Mayor,

the Aztecs performed ceremonies to Huitzilopochtli

to ensure the continued survival of their society.

If they didn't, it would be a catastrophe.

The Aztecs believed that we are living

in the fifth creation of the world -

there have been four versions of the Earth before -

and that each of those was destroyed.

They also believe that the fifth age will be the last age,

and so at the end of this world will come the apocalypse.

To stave off Armageddon, the Aztecs had to perform regular rituals.

They're living in a really fatalistic way,

and this is why they believe that they have to nourish their gods

and support them - in order to keep the world going.

For the Aztecs, pyramids were the only way

they could appeal to the gods

and make sure the sun would rise and life continued.

At the build site,

David and Lucas have laid out the footprint of their pyramid

and prepared the foundations.

After looking at our foundations, I think the Aztecs would be pleased.

I think that we're doing a good job.

Now they can start the challenge of building the monument itself.

They're attempting something that has not been tried

since Aztec times.

The first job is to prepare the stones for the pyramid walls.

This is grey tezontle.

And we're going to use this for the outside of our pyramid,

because it's a little bit stronger

than the softer red tezontle we're going to use for the core.

You can see right now that all of these are pretty rough,

that's not going to work for our pyramid.

We're going to need to use hand tools,

to chisel down flat sides on all of these stones.

Guilds of Aztec craftsmen worked on a production line,

cutting, shaping,

others preparing mortar or laying the stones.

We're basically using the same techniques as the Aztecs,

the only difference is we're using metallic tools.

But I think the banging of the stones and everything

is exactly the same as the Aztecs did.

Even with metal tools, it's a slow and difficult process.

The stones are uneven,

not perfectly shaped blocks like the ones used on Egyptian pyramids.

Lucas's next challenge is to work out how to fit them together.

OK, so right now,

we're more or less arranging some of the stones to see if they fit.

It's sort of like a puzzle. Got it.

So we're kind of like making our own puzzle pieces in a way.

Exactly.

And then, for example, if this is bothering the puzzle,

you just chip it off. Ah!

And then you can fit it better.

Each stone must be perfectly flat

to create the smooth outer finish of the monument.

Baltazar is going to sort of, like, flatten even more this...this stone.

So he's just seeing the little bumpy parts

and taking them out with the chisel. Got it.

Oh, man, there's a lot of chips coming off of this.

Oh, I just got hit again!

Man, so, for the Aztecs,

just thousands of people working at the site

doing something like this, chips flying around everywhere.

With the stone-shaping squad hard at work,

the construction team begins to build.

It's crucial they make sure the sloping sides are

at the right angle.

If we get the angles wrong at the bottom,

it's going to affect everything

in a much more visibly noticeable way.

As we keep getting closer to the top,

the pyramid's going to just look all kinds of crazy.

David also worries the foundations may not be strong enough

to support the weight of the entire pyramid.

As our pyramid starts getting bigger,

it's going to start getting heavier,

and I think the chance of it sinking down into the ground is

going to increase,

just as well as the walls possibly collapsing in on each other.

So it's really as we keep going

that I start getting a little more nervous.

After four days of precision craftsmanship,

finally, the walls of the first layer are complete.

David thinks the Aztec king would be pleased with their progress so far.

It's really starting to take shape.

I mean, this looks like an Aztec pyramid.

We had it on the design,

but to actually see it in real life,

I am beyond excited to keep going.

The lost Aztec world is slowly giving up its secrets -

magnificent ancient monuments,

an eerie tunnel, hidden for almost 2,000 years,

and a priceless manuscript are finally revealing the truth

about the powerful Aztec civilisation.

But as the team continue to build their Aztec pyramid,

they will solve even more mysteries

about what it took to create some of the most magnificent temples

the Americas had ever seen.

Next time - what can an ancient cemetery reveal

about how the Aztecs grew their powerful empire?

IN SPANISH:

How did they feed their rapidly expanding population?

IN SPANISH:

And what really happened during Aztec rituals?

The person would be stretched back over a sacrificial stone.

And in the middle,

you can see another priest is taking the heart out.

Subtitles by Red Bee Media