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...

..to spectacular drawings that may

explain the truth

about their origins.

Will these extraordinary clues,

and a pioneering attempt

to build a real Aztec pyramid...

What I'm learning so far about this

is how much labour it really takes

to build some of these structures.

..shine a light on the incredible

secrets of the Aztecs, and reveal

what life was like inside one of the greatest

empires in history?

In the 15th century, the Aztecs

built the most formidable empire

in the Americas and ruled over one of the largest

cities in the entire world.

At its heart, they built astonishing

pyramids to worship their gods,

and drew on resources from all over

their sprawling empire to do so.

Today, archaeologists investigate how they controlled

such a vast territory.

A clue lies here, in Metepec,

55km west of Mexico City.

On this hillside, archaeologists

made a gruesome discovery -

the skeletons of 118 men and women.

Some were buried in shallow graves.

Others, nearly two metres deep.

Many skeletons were buried lying down,

but a few had their knees bent.

Some were buried with pottery.

Others, without.

All these skeletons date from

the 15th century -

the height of Aztec rule.

What can these burials tell us about

the might of the Aztec Empire?

Archaeologist

Carmen Carbajal examines one of

the extraordinary skeletons found in the cemetery.

The size of the bones and the skull

suggest this was a man,

around 35 years old.

Beside his jaw, a dark stone

gives Carmen a clue about his life.

The body was found with offerings, to help him

into the afterlife.

Can they tell Carmen

where he came from?

The offerings prove

this is an Aztec skeleton.

But many of the dead

found here were not buried with the same offerings.

Carmen believes that

some of the skeletons aren't Aztec.

They were from the local Matlatzinca tribe.

Why bury the Aztecs

next to the Matlatzinca?

After defeating the Matlatzinca,

the Aztecs absorbed them into the empire.

The Matlatzinca started to fight in Aztec

armies, and the two tribes lived side by side.

The Aztecs co-existed with their former enemies.

Carmen wants to find out more about how they established control.

In nearby Calixtlahuaca,

archaeologists have discovered a clue.

Unlike most Aztec monuments, this structure is round.

Can these circular walls tell Carmen more about how the Aztecs ruled?

Temples honouring the Aztec Wind God don't have a specific orientation

They're built to be easy for the wind to flow around

and to reflect that the wind comes from all directions.

Carmen goes inside to investigate.

She discovers a fascinating secret.

This is not just an Aztec temple,

there are older stone structures hidden inside the building's walls.

The remarkable round temple has another temple inside it.

When the Aztecs took control of the region,

they didn't destroy the old structures.

They simply built theirs over the top.

The temple is a potent example of how the Aztecs imposed their rule.

The Aztecs didn't just conquer the Matlatzinca,

they took over the entire region.

What was daily life like in the cities they ruled?

This is Tlatelolco.

600 years ago, this was

the second most important city

in the whole of the Americas.

Located 2km from

Templo Mayor, Tlatelolco was

the trade capital of the Aztecs.

At its heart was a grand ceremonial complex,

with a magnificent pyramid

at the centre.

Its market was the largest

and most important in the empire.

Visited by 25,000 people every day.

Tlatelolco was the Aztec seat of commerce.

But now, new excavations reveal

dark secrets hidden in the centre of the city.

Archaeologist Salvador Guilliem

is excavating an incredible new site in Tlatelolco.

It's called The Great Basement.

He hopes it will shed light on how the Aztecs used

ceremonial buildings

in cities across the empire.

The black stone on the floor,

and the red stone decorating the walls,

mean this building could have been

dedicated to the God of War.

In this ceremonial building,

Salvador's team has found a series of rooms

arranged around a central altar.

They are unearthing pottery,

and incense burners.

But they've just discovered something shocking.

Human bones.

Here, people were sacrificed,

to honour the gods.

Ceremonial monuments like this

were key to Aztec society...

..but the secrets of how they were built

have been hidden for centuries.

At a construction site outside

Mexico City, archaeologist David Walton

and architect Lucas Cantu

continue their ground-breaking

experiment to build

a replica Aztec pyramid.

David and Lucas have finished

the first tier of their pyramid.

Now, they need to build high.

So, right now, we're starting

with the second layer,

and all the strings are marking

the proper angles and the levels,

and we're just building and building according to that.

While adding extra weight to

the top of the pyramid,

the team must figure out how the Aztecs would have stopped

their pyramid walls from caving in.

With sloping walls, if there's nothing to help kind of

hold them up, they will collapse

in on themselves.

They pack ground tezontle -

a volcanic rock - into the pyramid,

to make the structure strong.

Egyptian pyramids

had tombs hidden inside them...

..but the tezontle proves

Aztec pyramids were solid.

Any offerings, or deposits,

made to honour the gods here at the pyramids

are actually going to be done, sort of, on the corners,

out in front of the staircase.

Or really, we would have put the offerings in

underneath the foundation of the pyramid

before we even started building it.

David and Lucas

must make sure their carefully-cut

stones will stick together

as the structure grows.

They experiment with

the Aztec method of making mortar.

All right, so, the first thing we have to do is

pulverise some tezontle.

Yep. How do we do that?

So, I have here some rocks

I already started

and then you sort of smash it all

together and do this. Ah.

OK. Now, David,

we'll try to sieve it.

So, now, we'll get some of the lime powder. Mm-hmm.

They mix the finely-ground tezontle

with powdered lime, which

the Aztecs made from limestone.

When you cook the limestones in high temperatures,

then you get, like, a reaction.

When you put water into them,

you get this chalky powder.

Can you please put some water in? Yeah.

So, this is what we'll use to stick our pyramid together?

Yeah, yeah, yeah, this is what's going to hold the pyramid up.

This mortar is crucial.

It's the only thing holding

the walls in place.

The entire experiment forces David

to rethink his ideas about how

the Aztecs built these monuments.

What I'm learning so far about this

is how much labour it really takes.

We're not talking about a process that happens

over the course of a week, a month,

we're talking years to build

some of these major structures.

Thanks to labour gathered from across the empire,

the Aztecs had the materials

and manpower they needed to build

their incredible pyramids.

But how did they maintain control

of people and resources?

In Tenochtitlan, David examines the ruins of the city investigate

how military might fuelled this Empire.

A clue might be in one of the buildings next to Templo Mayor.

As archaeologists were working on the Templo Mayor,

they discovered a new structure to the north.

Outside, a staircase is flanked by sculptures of eagles

and a carved wall of skulls stands nearby.

Inside are benches decorated with processions of warriors.

Two statues of Mictlantecuhtli, the God of Death,

were found at one of the entranceways.

His ribcage is exposed, and his liver is hanging out.

We might look at the sculpture and think of it as terrifying, gruesome,

something not pleasant to look at, but the Aztec really connected the

ideas of life and death and actually want to move from life to death.

All these links to war and death mean this building must have been

one of the most important structures in the Sacred Precinct of the city.

The House of the Eagle Warriors.

The Eagle Warriors were the elite class of Aztec warrior.

Here in the House of the Eagles they meditated, prayed,

held ceremonies and organised their troops together in this spot.

Sons of noble families received extensive military training

to turn them into Eagle Warriors.

The Aztecs most feared fighters.

They had a headdress shaped like an eagle, shields decorated with

feathers, and spears with razor sharp obsidian blades.

But many Aztec weapons, like the atlatl spear catapult,

were not designed to kill, but to stun.

The main job of an eagle warrior was to take prisoners

so they could be used as human sacrifices to please the gods.

The Aztec elite warrior ranks like the Eagle Warriors were

really the driving force, the secret weapon for how the Aztecs

were able to conquer and subjugate people around Mesoamerica.

The Eagle Warriors at Tenochtitlan were at the heart

of an impressive military alliance.

To help control their Empire,

the Aztecs joined forces with Texcoco to the east..

..and Tlacopan in the west.

The alliance rapidly grew,

conquering an area of around 220,000 sq km.

Stretching all the way to both coasts

and down to Guatemala in the south.

Despite their skill and sophistication,

the Aztec military still remains shrouded in mystery.

What did it take to become part of this elite army?

80km southwest of Templo Mayor, at Malinalco,

archaeologist Beatriz Zuniga - hunts for a temple,

that could reveal more about the elite Aztec warriors.

To find it, she must climb 427 steps to the top of a hill,

120 metres above the valley.

At the top, Beatriz discovers unusual animal statues

flanking the steps leading to the temple.

The jaguar statues reveal that this temple was used by another

elite division of Aztec soldiers...

..the Jaguar Warriors.

Beatriz investigates the temple.

Inside she finds three seats.

Two are eagles with their wings spread,

and one is sculpted in the shape of a jaguar skin.

The seats reveal that Jaguar

and Eagle Warriors met here to perform rituals.

She finds something even more intriguing.

In the centre of the room there is an altar,

and behind it, a circular hole in the floor.

Aztecs who wanted to become Eagle or Jaguar Warriors would come

here to sacrifice their blood to the gods in initiation rituals.

They'd become part of a fearsome warrior class, ready to fight

and kill for the Empire.

What happened to the people they conquered?

At Sheffield University...

..historian Caroline Dodds Pennock

turns to the Florentine Codex to find out what happened to the

people defeated by the Eagle and Jaguar warriors.

This picture, although it's obviously not to scale,

is a really excellent representation of how human sacrifice was

practised in a sort of everyday way in Aztec culture.

You would have five priests, one holding each limb,

and the person would be stretched back over a sacrificial stone.

And in the middle, you can

see another priest is taking the heart out.

During a sacrificial ceremony the victim, usually a prisoner

of war or a criminal, would be led up the steps to the temple.

Aztec priests would slice open the victim's chest,

cut out their still beating heart and offer it to the gods.

It's estimated the Aztecs may have sacrificed over 20,000 men,

women and children every year.

What seems gruesome now was a divine necessity for the Aztecs.

To them, sacrifice kept the gods happy

and made sure the sun rose each day.

Offering human life to the gods was crucial for the Aztecs.

And death was just the start of the victim's role in the ritual.

In Calixtlahuaca, experts look for evidence of what

happened to the bodies of people who were sacrificed.

Archaeologist Carmen Carbajal finds a clue,

small circular stones sticking out of a curved wall.

These stone skulls reveal the gory truth of what happened to the

victims after they died.

The skulls were displayed to show off the Aztecs' power

and terrify their enemies.

The pyramids were important

because the location of a sacrifice was critical to its success.

David and Lucas now face their biggest challenge as they try

to discover exactly how the Aztecs built them.

At the construction site,

the second tier of the Aztec pyramid is complete.

Now work begins on the third, and final, tier.

As the pyramid gets bigger, the team faces the most difficult

challenge the Aztec workers had to overcome.

One of the challenges we want to think about, in terms of the height

of our pyramid, is how do we get those blocks up to the next layers?

And especially when we think about the Aztecs,

they had a much greater difference,

in terms of the height of their different tiers of their pyramids.

You can imagine blocks falling down,

maybe hitting people on the head, causing injury, you know,

it was another sort of peril of this Aztec pyramid building process.

This was exhausting, dangerous work.

David believes the Aztecs persevered

because it was crucial to their world.

Building temples like this really tells us that this

was a labour of love.

This was something the entire community cared about.

This wasn't one person at the top just saying,

"Ah, go and build me a pyramid."

You know, this is an entire civilisation saying,

"We need this, let's put our labour into this, our blood, sweat and

"our tears and let's make a pyramid for all of us to benefit from."

David needs to add the red tezontle stone

he chiselled earlier to the pyramid.

The team fit it into the wall.

To have carved this by hand out of the quarry, brought it here

and see it in the pyramid, that is just awesome, it feels really great.

Building these pyramids would have involved almost everyone in society.

What was their life like under Aztec rule?

Today, in Tenayuca,

researchers are learning more about the lives of the Aztecs.

Archaeologist Beatriz Zuniga investigates

the remains of an ancient suburb.

The Aztecs had a rigid class system, which dictated how they lived.

Beatriz searches the ruins of a house to find out who lived here.

This wealthy family added rooms to their house over time.

Houses became larger as families grew.

In the Aztec Empire, parents, grandparents,

and children all lived under one roof.

A fast-growing population meant the Aztecs had a large

pool of labour with which to build the pyramids.

Feeding a workforce of this size was another Herculean challenge.

At its height, the Aztec capital, Tenochtitlan,

was home to up to 200,000 people.

But it was isolated, built in the centre of a lake.

How did the Aztecs get their food?

Xochimilco, a site 25km south of Templo Mayor,

could hold clues to help solve this mystery.

Here, agricultural expert Ricardo Rodriguez investigates how the

Aztecs farmed.

Today, Xochimilco is a thriving farming district,

but 1,000 years ago there was no land here at all.

It was all water.

Where did the land come from?

These fields are called chinampas.

The Aztecs who lived in Tenochtitlan didn't have land for growing

food or raising animals.

So they built these fields from scratch.

Each chinampa is about 30m long and 3m wide.

At the height of the Empire, they covered almost 90 square km.

Ricardo steps ashore to take a closer look.

Ricardo meets Chucho, who farms the chinampas here today.

They use the tools and techniques of the ancients

to build a model chinampa, to investigate how the Aztecs did it.

Chucho's team must make sure they secure the stakes

firmly in the lakebed.

If they're loose, the entire structure could collapse.

Next they use branches and reeds to bind the stakes together

and fill the centre with grass to create an island.

The team then add layers of mud to bind the chinampa together.

Finally, it's time to test if it's strong enough for people to farm on.

Chucho takes his first step onto the new chinampa.

Great job!

The experiment is a success.

The team plant willow trees around the edges of the chinampa to

hold it together.

Man-made islands like this one helped sustain the growing

Aztec Empire.

The chinampas fed the large population at Tenochtitlan.

But there was another problem facing the Aztecs.

If the lake water is salty...

..how did the Aztecs living in Tenochtitlan get drinking water?

In Texcotzingo,

30km east of Templo Mayor,

archaeologist Martha Hernandez hunts for evidence that could help

solve this mystery.

Texcotzingo was built in the 15th century by an ally

of the Aztecs, King Nezahualcoyotl.

This was his royal retreat.

Martha searches the site for clues.

She finds a curious stone ruin.

To help channel water around Texcotzingo,

King Nezahuacoyotl built an aqueduct 8km long,

60m above the valley floor.

It transported water from springs high on nearby Mount Tlaloc

through a system of channels, with pools to regulate the flow of water.

This aqueduct reveals that the Aztecs were advanced

hydraulic engineers and they put this skill to use at Tenochtitlan.

They floated beds of reeds onto Lake Texcoco,

and anchored them down with wooden stakes.

Then they loaded earth, mud and stones on top until the mats sank to

the lake floor, creating artificial islands just a few metres apart.

On top they built troughs from packed clay which they

connected with hollowed out wooden logs.

This way they created a 4km pipeline to channel

water from the hills across the salty lake, and right

into the heart of the city where it was delivered into people's homes.

Ambitious engineering projects like these would have required

colossal amounts of human labour.

They are a testament to the might of the Empire.

From aqueducts to pyramids,

the Aztecs proved themselves to be sophisticated builders.

Can a modern-day construction team decode the engineering

secrets behind their success?

At the build site,

the tiers of the pyramid are complete.

Now Lucas investigates how the Aztecs used limestone to

decorate their monuments.

Stucco is basically limestone that is cooked and then it is grounded.

To get the perfect stucco,

Lucas mixes lime with water to create a paste.

Getting the right consistency is a challenge.

Too runny, and the stucco will drip down the pyramid.

Too thick, and it may crack as it dries.

We want something like peanut butter or even guacamole,

which is viscous, but not runny.

Because it was used to decorate pyramids,

lime was extremely valuable to the Aztecs.

They collected it as a tax, known as 'tribute',

from conquered regions across the Empire.

Some of the pyramids would be covered in white plaster,

but many Aztec monuments were decorated with a mix of colours.

Lucas and David decide to dye the stucco red with a mineral, hematite.

This is actually one of the most common minerals in a landscape

that you can find.

Red velvet cupcake batter!

I'm hungry.

With the red stucco ready to go...

Yes, that's going to be perfect for our pyramid.

..Lucas wants to test it.

The rock is very porous, in a way we just want to fill the gaps

and get an even surface, and try to smooth it out as much as possible.

Yeah, the colour looks really good, it's looking pretty consistent.

Lucas and David have solved one of the most important mysteries

surrounding Aztec pyramids.

They discovered how they were viewed by the Aztecs themselves.

Imagine this, it would have been gleaming, it would

have been bright, it would have been an amazing sight.

The Aztecs seized materials from across their empire to

build their pyramids, proof they were a powerful force.

So how and why did this mighty civilisation collapse?

Caroline examines the Florentine codex

to search for clues to their downfall.

This is a really fascinating

picture of the Spanish landing

on the coast. What we have are

these big European ships, which

the Aztecs would never have seen before.

They called them towers in the sea.

Hernan Cortes was

a Spanish conquistador.

In 1519, he sailed to Mexico

to conquer the land, with 500 men.

The Aztecs would have been amazed

by some of the things that the Europeans

brought with them. They would never have seen metal weapons,

they'd never seen guns before. The guns created

a huge impression because

it was like they were wielding

lightning or thunder in some way.

They've never seen cattle,

or horses.

These are an amazing demonstration

of the sorts of things that would transform the Aztec world.

Even with horses and metal weapons,

the Spanish were massively outnumbered by the Aztecs.

Conquering them should have been impossible.

Caroline thinks a clue to Cortes' success

lies in the faces of the soldiers

fighting alongside his men.

This picture shows us

a combination of Spanish warriors

and indigenous soldiers.

So, you have the Spaniards here

on horseback in armour, very clearly

distinguished from the indigenous warriors,

walking with their shields.

Cortes convinced the Aztecs'

local enemies to join him.

And soon, he was ready to take the fight to

the Aztec capital itself.

When Cortes and his army arrived in Tenochtitlan,

they marvelled at its size and sophistication.

The Aztecs offered Cortes gold,

a gift to convince him

not to wage war on the city.

But the Spanish slaughtered

the nobles and took the Aztec king,

Moctezuma, hostage,

until the Aztecs drove them out.

The Spanish returned with

an even bigger army

and destroyed the city, killing

nearly a quarter of a million

people in their conquest.

This brutal defeat was the end of

the once-mighty city of Tenochtitlan.

But what about the rest of the Aztec Empire?

In Tlatelolco,

David Walton investigates

how the conquest ended.

The sign says, "On August 13th, 1521,

heroically defended by Cuauhtemoc,

Tlatelolco fell to the power of Hernan Cortez."

Tlatelolco was the last holdout of the Aztec Empire.

This was their final defence, after the Spanish defeated

the Aztecs at Tenochtitlan.

This is the site of their last stand.

The final battle. The ultimate defeat.

David thinks he's discovered why

so few Aztec pyramids remain today.

Looking at this church, we can see

that's tezontle. That's the building material

the Aztec used for their temples.

And the Spanish took all of those temples down

and used that same tezontle stone

for their new constructions.

The Spanish conquerors used the stones from the Aztec pyramids

to build their on places of worship on the same site.

It was a symbolic way of demonstrating their power.

But even with local allies,

metal weapons and horses,

how was it possible for the Spanish

to defeat the Aztecs so completely?

David thinks they owed their success

to something else.

One of the things that contributed to the conquest

was the Spanish brought diseases with them like mumps, measles

and smallpox that really decimated the local populations.

It's estimated that by 1520, smallpox had killed

40% of the local people.

The Spanish decimated the Aztecs,

and wiped out their knowledge of

how to build the extraordinary pyramids.

How will David and Lucas

attempt the final, and most difficult, part of their pyramid,

without a guide?

Lucas and David must experiment,

as they start on one of the most challenging

parts of their pyramid, the steps.

Our steps are probably the most important part of the pyramid.

The whole purpose, or function, of

an Aztec pyramid was for people to both

be able to climb to the summit

and for priests to conduct rituals on top.

They use traditional techniques

to mark out the balustrades and steps,

keeping them level the same way

the Aztecs would have done.

I'm pretty sure they used strings.

They were probably made of some

organic agave fibre, or something. Mm-hmm.

Building the steps requires

total precision.

The stones must be shaped

on not one, but two sides.

And like the Aztec staircases,

these steps must be perfectly symmetrical.

With the staircases, the challenges are really...

making sure that the balustrades,

and the stairs themselves, look like sculpture.

When we look at it, it's got to be

absolutely perfect.

Once they've finished...

..this ground-breaking pyramid is

finally complete. David

and Lucas have gained a real understanding

of just how important the pyramids

were to the Aztecs.

I'm at the top of this pyramid

and it feels so awesome!

I can see the surrounding valley.

I really have a sense that

I'm raised up above everyone else,

just like an Aztec priest would have been

conducting rituals, here on this spot, say 700 years ago.

The pyramid is almost two metres high,

with a base five metres across.

Building it took five weeks,

20 tonnes of stone and mortar,

and a team of 12 workers.

Yeah, Lucas, wow, look at this!

This is awesome! Look at how the mortar

seems to be holding up really well.

Yeah, I mean, everything's

holding up together and, er,

I even like we added some of the raw stone

with organic matter. Yeah, organic matter on there.

I really like the cornerstones. They come to a nice, clean point

and it's all consistent running down the sides.

Yeah, the geometry is quite good.

Yeah that was the hardest part, right?

Taking this crude stone and getting geometric shapes out of it.

Yeah, it's almost like a sculpture if you think about it.

By building a pyramid from

the foundations up...

..carving the blocks by hand...

..and stacking them layer by layer

to create a masterpiece...

..the team has revealed the lengths to which symbolism

and ritual informed

every aspect of Aztec life.

I've always admired the Aztecs but now, by building this,

I admire them even more.

Now, the immense skill

and sophistication of

the Aztec engineers

is uncovered in all its glory.

Having done this, I just think it really gives me

a better sense of how much skill

the Aztecs had, how good they were at engineering

and, really, they were

an impressive society,

one we really need to think about and pay attention towards

when we're thinking about all the societies in the ancient world.

Every day, archaeologists

learn more about the Aztec Empire.

From magnificent monuments

to stunning ancient manuscripts,

experts are finally starting to piece together

the unique world of the Aztecs.

The Aztecs turned a small, marshy island into

one of the greatest cities of its time.

At its heart, they built an extraordinary pyramid,

dedicated to their most important gods.

They provided their huge population

with food and fresh water,

channelled in from kilometres away,

and lived and died alongside

their conquered neighbours.

All this created one of the most

advanced and powerful empires

ever seen in the Americas.

Today, many of the Aztecs' secrets

may still lie hidden

underneath modern Mexico City...

..but piece by piece, archaeologists

are bringing the mysteries

of the past into the light.

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