Unearthed

Teotihuacán, Mexico... a 2,000-year-old megacity

built around one of the largest pyramids on the planet.

Teotihuacán is remarkable and unique.

The scale of it, its degree of planning

are really phenomenal.

Today, teams are investigating

inside the city's many pyramids,

revealing gruesome discoveries...

We think they are buried alive.

...and unearthing hidden treasures.

But what were these massive pyramids for?

Who built them?

And why was this once-great city abandoned

just 900 years after it was built?

Blowing the pyramids apart,

we'll reveal the hidden clues

inside these ancient wonders...

their secret tunnels

and sacrificial burial chambers,

exposing the dark secrets

at the heart of this mysterious city.

captions paid for by discovery communications

the ancient city of Teotihuacán...

an archaeological gem in the heart of Mexico.

Incredibly, this single site was once home to 100,000 people.

Giant pyramids tower over the city center,

lined up along a central Avenue.

The remains of government buildings sit alongside,

surrounded by the homes of the elite.

And in the fields beyond lies evidence of ancient suburbs

that stretch out for miles.

This sprawling Metropolis was built 1,000 years

before the ancient Aztecs Rose up.

But nobody knows for sure who the Teotihuacáno were

or why, just 900 years later,

this civilization seemingly vanished.

Teotihuacán was the biggest city in the Americas

in the first half of the first millennium.

But there's still a lot we have to learn

about the Teotihuacános.

Today, teams of archaeologists

use advanced scanning and forensic technologies

to reveal hidden clues

and unearth Teotihuacán's deepest secrets.

David Carballo has been studying this ancient civilization

for 18 years.

He believes the best way to understand

who the Teotihuacáno were

is to explore the city's ritual landscape

that flanks its main road...

the street of the dead.

You have to imagine, back in classic period times...

1,500 years ago or so...

there probably would have been people gathered

in the street of the dead,

and from just about anywhere in the city,

you could see rituals.

The most important ritual structures on the street

are Teotihuacán's three massive pyramids.

The largest is also the oldest.

The ancient Mexicans built this vast shrine

around the time Jesus was alive,

and some believe they dedicated it to the sun.

The pyramid of the sun is a man-made mountain

clad in a layer of cement and stone

which gives shape to its rough heart.

Millions of tons of earth and sand

pile up layer upon layer.

On the outside, 248 cut stone steps

lead all the way to its towering peak

over 200 feet above the city.

The sheer scale of this stone Goliath

shows just how important

religion was to the mysterious civilization

that founded this city.

David believes

the ancient Mexican priests climbed the pyramid

at key times in the celestial calendar

so they could be closer to their sun god.

So, we are now at the summit of the sun pyramid.

We're on top of the world, as far as that goes,

right here in the Teotihuacán valley.

The sun pyramid would have been

one of the most spectacular monuments of the ancient world.

We have a lot of imagery that's suggestive

of fire rituals happening in the sun pyramid...

the sorts of rituals

which would not only commemorate big calendar endings

but also some sort of accession-to-office events.

So, it would be a real place of spectacle and pomp.

The earliest Teotihuacáno

needed height to worship their god,

but, surprisingly,

the pyramids built by later generations

were relatively short.

Why?

David believes that the Teotihuacáno

were a civilization capable of significant cultural change,

including the invention of a new cult

to worship a different god.

This is the feathered serpent,

which gives the pyramid its name.

You can see the rattle elements,

telling you that this is a rattle snake,

and then also the feathered elements on the body,

that this is the feathered serpent.

The Teotihuacáno came to believe

that the feathered serpent created the world.

And in 200 a.d., to honor their newly-elevated god,

they constructed a work of unsurpassed complexity.

Teotihuacán is the origins of this god,

at least as a primary god,

who completely decorated a pyramid.

And what it really represents is a new effort

on part of the Teotihuacán to highlight this god.

The outside of the feathered serpent pyramid is stunning,

but it's the inside that truly takes the breath away.

Instead of a simple pile of mud,

the core of this building

is a complex, man-made honeycomb of rock and mortar.

Five distinct layers of construction

are bound by thick walls.

Rubble fills the spaces between, creating modular cells.

They come together to make huge, solid building blocks.

This advanced design suggests

the Teotihuacáno's building skills were evolving

in step with their changing religion.

But why did they create such complexity

in a part of the pyramid that would never be seen?

David believes the reasons were practical, not ceremonial.

The geometric design

made the core of the pyramid super strong.

The ancient Mexicans could then cement

over 400 giant, carved heads to the outside

without the whole structure collapsing.

These are beautiful sculptures,

and the fact that there are so many of them

on all four facades of this building

attest to the immense amount of labor

that went into constructing this monument.

The feathered serpent pyramid displays precision engineering.

To build this complex modular design,

the Teotihuacáno had to create

a completely new way of constructing their pyramids,

using four distinct building materials.

The first material was wooden posts,

used to Mark out a precisely aligned grid

and create a sturdy scaffold.

Then they clad this wooden skeleton

with mud, mortar, and volcanic stone

to build a honeycomb of strong structural walls.

They packed the cells with more volcanic rock...

super strong, but too rough to be used

on the outside of the building.

Finally, the reserved their finest material

for the exterior... high-quality slabs of stone

decorated with elaborate sculptures.

This new religion of the feathered serpent

was ground-breaking and incredibly significant,

going on to influence both the Mayan

and Aztec civilizations.

It is at Teotihuacán where we see the major origins

of this cult to this deity,

who then becomes important within mesoamerica.

Invigorated by their new religion,

the Teotihuacáno put their advanced building skills

to good use.

They provided their growing population

with a perfectly geometrical city grid

of buildings and homes.

And deep below the pyramids,

archaeologists have also discovered secret tunnels.

Could these be evidence of a bloody ritual practice?

In Mexico,

investigators are unraveling the secrets

of a 2,000-year-old mystery...

why was the ancient pyramid city of Teotihuacán built?

Archaeologist Sergio Gómez Chávez

is searching the city's giant pyramids for clues.

He believes one key is to understand

how they were used.

The largest pyramid in Teotihuacán

hides a surprising secret.

Directly beneath the pyramid of the sun,

archaeologists unearthed a tunnel in the bedrock.

First, they thought it was a natural cave,

until they hit a carved-out chamber

and beyond it, the remnants of 17 thick, man-made walls

built to block access to the tunnel.

At the very end of the tunnel,

they found an elaborate chamber

carved in the shape of a clover.

Whatever this subterranean vault was designed to hold,

it was meant to be locked away for eternity,

buried under millions of tons of rock.

Now the tunnel lies empty.

Ancient robbers most likely stripped it bare

hundreds of years ago.

But the discovery under the sun pyramid

was just the beginning.