Original subtitles

25.000

BBC Natural

Hidden in this jungle

3000 years of human history

one of the world's greatest ancient civilisations.

Here, on Mexico's Yucatan peninsula,

the Maya built cities, temples and palaces

and yet we still don't know how they thrived.

The forest has grown back

and nature has taken over again,

leaving many riddles unsolved.

Like the riddle of the missing river.

Almost every other ancient civilisation was founded beside a great river,

but there are none here,

not even any streams.

Where is the Nile?

The Ganges or the Euphrates of the Maya ?

What they did have

were thousands of these pretty little pools scattered through the jungle.

Called Cenotes,

they are the Yucatan's only source of fresh water.

Could they, by themselves, have supported an entire civilisation?

The Maya believe that Cenotes

were entrances to another world,

an underworld.

At face-value they seem to be little more than beautiful jungle waterholes,

so was the underworld just a myth?

People today can do something the Maya could only have dreamt about

breathe under water.

These modern explorers have made some remarkable discoveries,

not only about the Maya,

but about the forest

and its animals, too.

What they have found in the underworld,

has changed our understanding of the Yucatan,

forever.

Secrets of the Maya Underworld -= MVGroup =-

The Yucatan,

a peninsula the size of England,

separating the Gulf of Mexico from the Caribbean Sea.

American-born Sam Meecham is a cave diver.

He has been exploring the waters under the Yucatan for more than a decade,

but he has still only seen a fraction of what is down there.

His mission

is to explore as many Cenotes as he can,

working with scientists to try to make sense of it all.

The puzzle of the Yucatan peninsula is extremely complex.

I arrived here in 1994 with the intention of only being here for six months,

and 10 years later, I find myself still here,

so interested and curious in what I have discovered.

But Sam wasn't the first foreign explorer to be drawn to Mexico's jungles by a passion for adventure.

Back in 1839,

John Lloyd Stevens, an American diplomat and travel writer,

set off into the Yucatan,

inspired by rumours of a lost civilisation.

For a while,

he found nothing,

even though clues lay all around him.

Finally,

he stumbled upon the ruins of a great city,

smothered by the jungle.

The wild tales that Stevens told

made his name as a famous Victorian explorer,

a hero of his time,

and to some,

the original Indiana Jones.

Stevens' fantastic revelations have inspired a whole new generation of explorers.

For me, one of great motivating factors in what we do here

is that I am able to explore, in the 21st century,

something I thought would never have been possible in my lifetime.

Just getting to the Cenotes is an adventure in itself.

Like the Maya ruins, they are scattered over thousands of square kilometres of trackless forest.

But Sam is not alone

British-born Steve Bogart shares Sam's passion for exploration.

They have been Cenote hunting together for years.

With local help,

they mount expeditions deep into the Yucatan's interior.

It can take days to find a new Cenote.

As we travel through the jungle looking for Cenotes,

of course there is always the usual assembly of spiny trees and cactuses.

We have crocodiles, we have snakes, scorpions, tarantulas, you name it, it's all there.

But really,

if you know what to look for and know where to go and when not go,

you can avoid a lot of these problems.

Finally, a new, unexplored Cenote.

Never mind the jungle treks,

the real danger for Sam and Steve begins at the bottom of these enchanting little pools,

considered sacred by the Maya.

It's very easy to see how the ancient Maya

would have perceived the Cenotes as very sacred spaces

they are absolutely beautiful jewels out in the middle of this jungle.

And to walk up to the edge of a Cenote and to look down

into the crystal clear water and see the fish swimming below in the natural daylight,

casting these incredible shafts of light through the water,

is very inspiring.

As the sole sources of water in this jungle,

these pools are also magnets for wildlife,

and to Cenote specialists like grebes,

their whole world.

With thick forest on all sides,

they seem as isolated as islands in an ocean.

Peccaries, deer and other forest animals use Cenotes as watering holes,

but that doesn't mean they are easy to see

the jungle does it's best to keep them hidden.

But some animals, you can't help but notice.

Howler monkeys.

Even if you don't see them at first,

you are sure to hear them.

With calls that carry five kilometres,

they are the loudest land animals in the world.

Howlers are sloppy eaters.

Coatis following below can fill their stomachs solely

out of what they have dropped.

Spider monkeys.

They are infinitely quieter than howlers,

but much more agile.

With their hooking hands and long arms,

these monkeys can live their entire lives in the dense forest canopy.

For nine months of the year,

there is no rainfall here,

and much of the forest struggles to survive.

But some trees seem immune to the drought.

What is their secret?

Such are the riddles of the Yucatan.

The answers lie underground.

But Sam and Steve won't get to go there until tomorrow.

In the dark,

the jungle seems even denser

and the sounds,

even stranger.

This is when Cenotes really come alive.

Tapiers love water,

for bathing, as much as drinking.

But visiting a Cenote means coming into the open,

which, for good reason,

they only do after dark.

Like watering holes anywhere,

Cenotes are where predators,

in this case Jaguars,

come to hunt.

But to the Maya,

Cenotes were more than just jungle watering holes,

they were central to their world.

Cities and temples were often built right next to them.

These sacred wells were gateways to the underworld

a terrifying place of spirits

and of fearsome gods who demanded respect.

At the bottom of many Cenotes

lie offerings made to the underworld.

For archaeologists,

Cenotes are time-capsules that provide clues to how the ancient Maya lived

and died.

Sometimes, even the people, themselves,

were sacrificed to the gods they feared so much.

Every pot and skeleton

has its own story to tell.

The discoveries of underwater explorers

are helping archaeologists rewrite

the Yucatan's ancient history.

Yucatan's explorers

aren't just interested in the clues to Maya history

that they might find at the bottom of these pools.

They want to know

what might lie beyond them.

Is there, indeed,

an underworld?

Could this Cenote be a gateway to a whole new world?

If it is,

where does that world lead?

Every new Cenote

presents a new opportunity.

Cenotes really present us with the truest form of exploration found today.

When we come up to the side of a Cenote,

we literally have no idea what we are going to find

at the bottom of it,

until we actually get in and investigate.

And, for me, that is one of greatest thrills about what we do.

Cenotes aren't just simple pools,

they are caves

flooded caves whose roofs have collapsed.

But Sam and Steve have yet to discover

to what extent Cenotes are connected to each other

by flooded tunnels.

If there is a network of flooded tunnels down there,

how far does it go?

What they are doing is carefully charting an, as-yet, uncharted part of the planet.

Somewhere no other human being has ever gone.

It's one of the riskiest things an explorer can do.

This type of diving isn't for everybody.

And, definitely, you have to want to do it, in order to be involved in it.

The first cave dive that I ever did, actually,

I was pretty nervous.

Talk to an astronaut that sat on top of a rocket full of fuel and blasted off to the moon,

sure I bet they were a little bit nervous,

but look at what we've gained through space exploration.

All those people were willing to take a risk to achieve an incredible goal.

Sometimes there is hardly enough room to squeeze through.

Getting stuck or damaging vital equipment now

would be fatal.

We are diving in an extremely hostile environment.

It is underwater, it's dark, it's easy to get disoriented

and therefore it is easy to have panic attacks.

There is two ways out of a panic situation,

luck and death.

And therefore, panic is not an option for us.

You really have to take three deep breaths, calm yourself

and assure yourself that you are able to get out of that situation.

Exploration is rarely without risks.

But one of the biggest rewards

is seeing something that has never been seen before.

What they have discovered down here

is just staggering.

The Maya did have an underworld.

And it is as strange

and as beautiful a place as any myth might describe.

They have revealed a vast system of flooded caves,

underpinning much of the peninsula.

It has changed our view of the Yucatan, forever.

In a sense,

this is like exploring outer space,

the weightlessness,

the utter strangeness,

the thrill of the unknown.

Cave divers call this inner space.

Sam has got close to a long held ambition.

One of my childhood dreams was to become an astronaut.

I am not an astronaut now,

but I feel that I am as close as I can come to outer space exploration

in the work that we do here.

We are completely dependent on life-support equipment,

we travel into a completely alien and foreign environment

that we don't know a whole lot about.

And many of the cave systems that we dive in

have seen fewer visitors than the surface of the moon.

It's amazing to think that a whole civilisation once sat on top of all this,

trying to imagine what was down here.

The reality of this place

can be as surreal as anything the Maya may have dreamt of.

Sometimes, what seems to be air, isn't.

It's just a different kind of water.

Some caves contain layers of water that just don't mix.

There is so much about this system that we don't yet understand.

Sam and Steve's aim is to find out how it all connects.

They are making maps.

Light ahead reveals a new Cenote.

They will record it's position,

then swim back to where they started the dive and try to return here,

overland.

The more they explore, the more connections they find.

But they have got a long way to go.

There are still thousands of Cenotes left to investigate.

The return journey is, in many ways, more difficult.

Underground, they went where the tunnels led them.

Up here,

they are looking for one tiny pool among thousands,

hidden somewhere in a dense jungle.

For this,

they will need satellite positioning and aerial photographs.

State-of-the-art technology gets them close,

but on the final stretch,

they get a helping hand from birds.

Turquoise-browed Motmots.

These are true Cenote birds,

they feed on the abundant insects near the water

and often nest inside the caves.

Their distinctive call

almost always means there is a Cenote nearby.

It was the ancient Maya who first used them as guides to water.

This works just as well today.

Now they have located the new Cenote,

Sam and Steve need to find out

if it has further connections with other parts of the system.

In our corner of the Yucatan peninsula,

the collaborative efforts of cave diving explorers have mapped

and explored over 550 kilometres of underground, underwater passageway

in over a hundred different cave systems.

The promise of future exploration is high,

there is so much left that we still have yet to explore.

This may seem like nothing more than an elaborate game of join-the-dots,

but each time Sam and Steve go back underground,

they never lose sight of the potential dangers of their work.

One of the truisms of cave diving is that 'complacency breeds death'.

And every single dive we approach as if it's the first dive we had done.

And we have a ritual that we go through of matching our gear,

checking for leaks,

and making sure that everything is in optimal 100% condition for diving.

Sam couldn't have a better dive buddy than Steve,

he is one of the region's most experienced cave divers

and a master technician.

He knows his equipment inside out.

OK, one of the first things you will notice

is that we are actually taking two tanks with us, rather than one.

That's because we are diving in an alien, potentially hostile environment,

and we need redundancy in all our life-support equipment

and gas supply is obviously very very critical to us.

We also use a gas management planning rule know as a rule of thirds,

so we would use one third of ou gas swimming into the cave,

one third swimming back out again,

so that when we surface we have one third in reserve.

And that is an emergency reserve,

should it take it us longer to exit than we anticipated

or if we needed to share air with a buddy.

A thin piece of white string,

carefully laid,

quite literally becomes their lifeline.

It may be the only way that they can find their way back

out of the labyrinth.

They mark it with arrows that always point back towards the entrance

and safety.

It is also a measuring tape

regularly spaced knots tell Sam and Steve how far they have gone.

As we explore the cave systems,

we try to be smart as we can

and generally, we are trying to go in a particular direction.

And we have compasses that work under water and using those compasses,

we are able to determine which route to take.

It is quite common to come up to a split in a passageway.

We have to determine which is the best route to take.

In some cases, that will end up in a dead-end

and we turn around and come back out and try the other way.

Using spools of string,

Yucatan's cave divers have measured the longest underwater cave in the world

over 133 kilometres long.

Exploration wouldn't be exploration if everything always went to plan.

This time,

the divers have come to a passage too tight to squeeze through

and they are forced to stop.

They follow their safety line back,

and live to dive another day.

But explorers wouldn't be explorers if they let such setbacks discourage them.

There is always the thrill of the next dive.

It's pretty-much guaranteed that every time we go into a Cenote

it is going to be a different experience, it's something new,

it's something exciting, and that's what really draws me in.

One of many interesting things of diving here

is to watch all the wildlife that thrives in the crystal clear water.

That includes sailfin mollies,

small fish

that stick to the bright sunlit zones in the open water pools of Cenotes.

For a male, it is a hectic life.

He has a three-dimensional territory to patrol

and is constantly chasing other males out

while trying to keep his harem of females in.

In both cases, success depends on how effectively he displays his sail fin.

It's a big job for a little fish.

Some fish, like these tetras,

have proved to be real opportunists.

They have learnt to follow divers' torches into the dark to feed right inside the caves.

Our divers take care not to bring any uninvited guests with them,

because the underworld has its own unique creatures

an entire food chain of over 30 species

that live out their lives in the pitch dark.

Most cave animals are white,

because in a world without light,

colour is pointless.

Even eyes are useless,

and many creatures just don't have them.

Down here,

touch and smell are all that matter.

Among the strangest and most ancient of cave beasts

is the remipede

a sort of primitive centipede that is rarely seen

found only in waters exceptionally low in oxygen.

Relics of one of the earliest chapters of life on Earth,

they are among the caves' top predators,

coming the water for shrimps and isopods.

If the remipede doesn't seem to know which way is up,

that's because,

in the water and in the dark,

up and down aren't so relevant.

In the underworld,

even the fish are surreal

ghostly white,

with blanks where eyes should be.

There are other signs of life down here.

This is the perfectly preserved tooth

of a Gomphotherium,

a relative of the elephant that has been extinct for 10,000 years.

Ancient animal remains,

and these stalactites and stalagmites

only ever formed in air,

are hard evidence that these caves used to be dry.

And Yucatan's history goes deeper still

the walls of these caves are made of soft limestone,

telling us that this was once a huge coral reef.

Some caves near the surface have air pockets

and cracks in their ceilings that allow bats to come and go.

Cave swifts, too.

It's the perfect sheltered place to roost and nest.

No wonder the Maya thought that bats were from the underworld.

They would have seen them flying straight out of the ground, as night fell.

By exploring underground,

Yucatan's divers are peeling back the many layers of the peninsula,

and are slowly revealing the incredible relationship between its flooded caves

and everything they affect at the surface.

There are many ways in which these two worlds connect.

Tree roots.

This is the jungle's secret.

How, with hardly any surface water,

it can still grow so dense.

Some trees and vines push their roots through gaps in the limestone

to the permanent water supply below.

It doesn't matter how dry it gets on the surface,

they rely on the underworld.

These deep-rooted trees provide animals with a year-round supply of leaves,

flowers and fruit.

This vital connection between the forest and the ground beneath it,

must have intrigued the Maya.

It could only have reinforced their belief in the power of the underworld.

They, too, relied on its gift of water.

A few Cenotes

could help a whole city survive even the harshest of dry seasons.

But Sam doesn't just look to archaeology for his understanding of the Maya

he can talk to them.

Direct descendants of the ancient Maya still live here.

One of them,

is Don Fermin Zippe,

a good friend of Sam's.

The Maya still practice slash and burn farming

growing crops then letting the forest grow back to replenish the soil.

In fact, the ancient Maya did this on a grand scale.

Incredibly,

most of the jungle here, previously thought to be pristine,

has actually been cut down and regrown many times over the last 2000 years.

The Maya may have stopped building large cities and temples,

but they live-on today as skilful farmers,

thriving, despite the thin soils and harsh seasons of the Yucatan.

Maya communities are close-knit

and the Mayan language is still spoken.

"Cenote" is derived from the Maya world word for "well".

Almost every village is built around one.

Other Cenotes mark boundaries between the communities.

Cenotes were, and are, quite literally

central to their world.

As well as a distinct language,

the Maya have a distinct set of beliefs.

Their stories and fables, passed down the generations,

describe everything around them

the Cenotes, the jungle, the animals.

One Maya belief is that the powerful forces of the underworld

determine their prosperity

and their destiny.

Don Fermin still practices the Maya religion.

He prays to the gods of his ancestors

and regards Cenotes

as windows into their world.

In advance of Sam's more difficult dives,

Don Fermin sometimes makes offerings to the underworld,

asking for a safe passage.

And this dive will be difficult.

But it will reveal yet another twist in the Yucatan's many-layered history

a cosmic event

that affected not only the world of the ancient Maya,

but possibly,

the rest of the world as well.

Some Cenotes near the north western tip of the Yucatan

aren't at all like the ones that Sam and Steve are used to exploring.

These are much deeper,

sheer, vertical sink holes,

known as "Pit Cenotes".

This Cenote is definitely a lot deeper than

ones that we normally would encounter.

Today we got to about 45 metres of depth and still we couldn't see the bottom.

This appears to be the bottom,

but it isn't.

It is a cloud of hydrogen sulphide,

made from rotting vegetation.

It is toxic and corrosive

not somewhere you would want to hang around.

The hydrogen sulphide layer is actually pretty intense,

as you are descending down into the Cenote,

it gives the appearance that you are coming up on the floor

and all of a sudden you realise it is not the floor, it is a cloud.

It is made up of sulphur, primarily, so it has got a rotten egg smell to it.

In extreme cases, where it is very strong,

you can feel it burning any exposed skin that you have.

Why are these Cenotes so different?

They are evidence of a critical turning point in the Yucatan's distant history

something that was only noticed 20 years ago,

when satellites gave us a new perspective on life on Earth.

If you look at normal Cenotes from space,

their pattern is scattered and random,

but the Pit Cenotes,

form a distinct semicircle,

165 kilometres across.

Seismic studies have shown that the circle is completed

under the sea.

So what does this huge circle represent?

The answer lies at least 65 million years ago,

when the Yucatan was a shallow tropical sea.

The disastrous event that caused the circle

was so massive, that some think

it could have led to the demise of the dinosaurs.

An enormous meteor,

heading for what is now the very tip

of the Yucatan peninsula.

Imagine at the moment that this meteor slammed into our planet,

it was so huge that if one edge of it was touching our planet,

the outer edge of it would be at the same altitude as a commercial jet liner flies today.

The immense impact crater

was gradually buried under limestone,

built up by coral reefs over millions of years.

But the crater's shape

was echoed in the way this limestone,

then eroded to form the distinctive semicircle of Pit Cenotes.

When the Maya arrived,

they built great cities and temples around these sacred wells,

unwittingly outlining the footprint of this global catastrophe.

Once again,

the Yucatan's history can be read by looking deep into its landscape.

But it has one more secret to reveal,

one last riddle to be solved.

When it does rain here,

it rains hard.

But this huge amount of water

doesn't settle on the ground,

it vanishes.

It seeps through the limestone

into the underworld.

But this freshwater is only the top layer

it floats above an enormous body of much heavier, salt water.

This is the halocline

the interface between the two.

It is this contrast between the gin-clear fresh water

and the hazier, salt water that can make diving here

so surreal.

Divers have discovered

that the freshwater here

does more than just float.

It flows,

in huge underground rivers,

probably the largest underground river system in the world.

Nearly two centuries ago,

John Lloyd Stevens rediscovered the Maya civilisation.

People have long wondered how they thrived without a great river.

Now,

we appear to have found their Nile.

These great rivers must flow out to sea,

but where?

Sam needs to find out.

He comes across the skeleton of a manatee,

a sea mammal.

He must be getting close.

Meter by meter,

Cenote to Cenote,

cave divers are mapping the rivers from source to sea.

But while doing so,

they have made an alarming discovery.

The modern world is taking over.

I am amazed at the change that has taken place in such a short time in this area.

It seems that every time I go out of my door,

there is a new building that has been built.

The coastal strip of Cancun and the Riviera Maya

is one of the fastest-growing tourist areas in the world.

There is one specific occasion where we were

actually diving beneath a major construction project.

And, as we were diving along, the entire cave was literally shaking

as we were diving through it.

And it wasn't until the next day that we came back

that we realised that they had been perforating through the ceiling of the cave,

and along one of the lines that Steve had laid the previous day,

there was actually a cement piling going right down through the cave system.

New construction could inadvertently block

or pollute the great underground rivers of the Yucatan

with far-reaching effects, still too complex for us to understand.

The Maya underworld

faces a new chapter in it's long and varied history.

The decline of the ancient Maya

could teach us a thing or two.

Some say they developed too far, too fast.

Others,

that a succession of droughts left them without water.

Everyone here still relies on the underworld.

It is, and always was, the lifeblood of the peninsula.

Without it,

the Yucatan would be a hot,

dry and hostile place.

By mapping the course of every river to the sea,

Sam and other divers are hoping to draw attention to them,

so further damage can be avoided.

Their work has not only helped us to understand the Yucatan's past,

but it can help to safeguard its future.

Sam's journey down this river

is nearly over.

There is more light and more air,

and the roots are roots of mangroves.

And there are manatees.

These gentle herbivores come to the underworld's outflow to drink fresh water

and to cool off.

What they mean to Sam,

is that he has made it.

One last tunnel,

and a journey that began in a jungle pool,

ends-up off a Caribbean beach.

Tomorrow he will be back in the forest,

looking for a new Cenote

and the next river.

And when all the Cenotes are explored and all the maps are finished,

maybe the Yucatan will be better understood.

In a more mystical way,

the ancient Maya understood it.

They knew they were at the mercy of the underworld.

At the ruins,

archaeologists are revealing ever-more about this great civilisation

how they lived,

and what they believed.

But now,

a whole new frontier has opened, underground.

Sam and Steve are not the first explorers to have been enchanted by the riddles of the Yucatan,

but they have, quite literally, taken exploration to a whole new level.

To this day, it is only thought that we have charted

a fraction of the Maya underworld

and many of these areas still remain untouched and uncharted.

Sam continues with his passion.

He certainly has his work cut-out for him in the coming years.

My feelings about exploration can be very easily summarised in a poem

I read about the Yukon goldrush.

And in that, the author says, "it is not the gold,

it's finding the gold".

It's finding the Cenote and diving down into it and seeing what is there

that really is the thrill for me.

Really for all of us,

it is a motivation to think that you can live in the 21st-century

and still be able to explore.

We are only just scratching the surface of what exists here.

I have absolutely no doubt that this place will continue to provide

incredible scientific discoveries for years to come.

Sam and his explorer colleagues

have risky,

yet fascinating days ahead of them

unveiling the many secrets

of the Maya underworld.

-= MVGroup =-