Original subtitles

NARRATOR: Helike,

one of the greatest ports of classical Greece.

This entire city, just like fabled Atlantis, vanishes

to all but legend for over 2,000 years.

Now, pioneering archaeologists believe they have

unearthed the ruins of this ancient metropolis.

NARRATOR: The investigation into Helike's fatal

NARRATOR: The investigation into Helike's fatal

final days inspires cutting-edge experiments

to test the true cause of the city's disappearance.

NARRATOR: Does a single wave devastate Helike?

Or does the earth itself consume its sacred stone structures?

[thunder crashes]

And could Helike's rediscovery lead the way to

And could Helike's rediscovery lead the way to

the most famous lost city of all, Atlantis?

To solve these mysteries,

we digitally reconstruct this bustling ancient capital.

We rediscover the lost monuments

once worshiped by the city's residents

and crack the mystery of why Helike is hidden for so long

to unlock the true story of Greece's real-life Atlantis.

to unlock the true story of Greece's real-life Atlantis.

50 miles from Athens is Greece's Peloponnese peninsula.

Somewhere along this coast lie the remains of Helike,

one of the great cities of ancient Greece.

Homer's Iliad describes its proud people

going into battle under King Agamemnon

during the siege of Troy.

2,400 years ago, the city disappears overnight.

Ancient texts describe a walled city-state that

thrives as Greek culture and military might dominate

the Mediterranean.

Its people worship the almighty Poseidon

and construct a temple and sanctuary in his honor,

as well as a giant bronze statue of the sea god.

In 373 BCE,

a disaster destroys the city,

and like Atlantis, Helike disappears.

What happens to the city, and where is it today?

What happens to the city, and where is it today?

One of archaeology's greatest quests is to find Helike

and unravel the mystery of the city's fatal final days.

Dora Katsonopoulou

has searched longer than any

other investigator to unearth this legendary metropolis.

NARRATOR: Luckily, she has help.

An ancient eyewitness leaves clues to

the location of the great lost city.

He spots Helike's ruins, five centuries after

its destruction,

and records the distance to two local landmarks.

First is the still-standing city of Aigion to the west.

First is the still-standing city of Aigion to the west.

NARRATOR: He also states the ruins are 30 stadia,

3 miles from a place known as the Cave of Herakles.

NARRATOR: Dora measures from the two fixed points.

NARRATOR: Helike's search area is today

roughly 2/3 land and 1/3 sea.

It means the city could now lie

underwater in the nearby Gulf of Corinth.

underwater in the nearby Gulf of Corinth.

NARRATOR: An eyewitness reports

Helike lies underwater

150 years after its destruction.

The sacred bronze statue of Poseidon still stands,

holding a half-horse, half-fish mythical beast,

holding a half-horse, half-fish mythical beast,

the hippocamp.

It snags on fishing nets passing above.

Four hundred years later,

another eyewitness describes the city.

Badly corroded from salt,

it remains a well known local landmark.

Does Helike lie hidden beneath the water today?

Starting in the 1960s,

guided by the ancient accounts,

guided by the ancient accounts,

Dora and others search for the lost city.

Experts use sonar,

divers,

and undersea drills to systematically probe

the seabed of the Gulf of Corinth.

They return empty-handed.

NARRATOR: Dora refuses to give up on the hunt for Helike.

NARRATOR: Dora refuses to give up on the hunt for Helike.

She re-examines the ancient eyewitness's description.

[speaking foreign language]

[speaking foreign language]

[speaking foreign language]

NARRATOR: The Greek word "poros"

means a narrow stretch of water.

Other experts assume this stretch of

water must be the Gulf of Corinth.

Dora thinks if the eyewitness spots the statue there,

he would use its proper name,

the Gulf of Corinth.

It must lie beneath a different stretch of water.

NARRATOR: If Dora's theory is correct,

she'll disprove some of the world's

greatest archaeologists.

The problem is the lagoon has long since disappeared.

Where might the lost city lie today?

And can its ruins reveal what

happens on Helike's fatal final day?

happens on Helike's fatal final day?

NARRATOR: The great city of Helike is destroyed in 373 BCE.

Its ruins are last seen underwater

nearly 2,000 years ago.

Fresh analysis of ancient eyewitness reports suggests

the city may not be lost beneath the sea.

It may lie under an inland lagoon that has vanished.

It may lie under an inland lagoon that has vanished.

[engine revving]

Dora's team searches for the lost lagoon

and the city beneath.

They drill 99 boreholes in

the region outlined by the ancient eyewitness account.

Lead Geologist Ioannis Koukouvelas examines

mud cores from the boreholes.

NARRATOR: The green tint dates this sample layer

to 2,400 years before the present day,

the time of Helike's great disaster.

The layer also contains the smoking gun

The layer also contains the smoking gun

the team is searching for -- signs of human occupation.

NARRATOR: The ceramics could be from Helike.

The team excavates around the most promising boreholes.

Beneath 10 feet of mud,

they uncover the remains of an ancient dwelling.

they uncover the remains of an ancient dwelling.

Inside, they find a small clay sculpture of a female idol,

fragments from a shattered vase,

and Greek coins, one featuring a pair of dolphins.

The finds reveal a settlement that dates to

the 4th century BCE.

If this is ancient Helike,

where is the evidence for the lost lagoon?

A clue lies 5 feet above the ruins --

a dark layer of sediment.

The finds suggest Dora's controversial theory that Helike

lies under a lost lagoon could be correct.

But the team needs proof

the dark layer corresponds to the bed of an ancient sea lake.

Ioannis examines the mud core close

up at the University of Patras.

NARRATOR: Ioannis scrutinizes the layer's contents.

NARRATOR: His team searches for any tiny shells.

NARRATOR: His team searches for any tiny shells.

They might not be much larger than grains of sand.

For precise identification,

the team creates images using an electron microscope.

These are creatures called ostracods,

particular species that prefer to live in the mix

of salt and fresh water found in a lagoon.

The presence of these ostracod species confirms Dora's theory.

Helike was covered by a lagoon,

which then itself disappears

thanks to this area's ever changing landscape.

Local rivers erode nearby mountains.

and fill with huge amounts of sediment.

Over many years, the rivers dump this debris

once they reach the coastal plain.

The buildup of silt produces new banks

and channels, drastically changing the local landscape.

It's likely the lagoon above ancient

Helike gradually fills up with river sediment.

The sea lake turns into dry land

and conceals Helike completely.

and conceals Helike completely.

Dora and the team's detective work

finally solves a centuries-old mystery.

They found Helike.

For 20 years,

the team digs deep trenches through

the sediments of the flat coastal plain.

They unearth several pockets of settlement that

span more than 2,000 years of occupation.

What can archaeology reveal about

What can archaeology reveal about

Helike's status in ancient Greece?

And could this help pinpoint the source of the Atlantis myth?

NARRATOR: Helike, Greece,

a long lost ancient city,

now rediscovered by Dora Katsonopoulou and her team.

NARRATOR: Among the ruins of Helike,

archaeologists unearth two identical coins.

archaeologists unearth two identical coins.

They feature important clues about the ancient lost city.

On one face, a laurel wreath surrounds

two dolphins swimming either side of a trident spear.

on the other, the head of the god Poseidon,

next to a single word in Greek, Helike.

What can these coins and the god

depicted on them reveal about the city?

NARRATOR: The great poet Homer, four centuries before

Helike's destruction,

remarks on great sacrifices made in Poseidon's honor.

The locals choose this particular god

because Helike is a port city.

NARRATOR: The citizens' fortunes depend on the sea

and, they believe, on the moods of its chief deity.

Poseidon is the brother of Zeus and Hades.

He carries a three-pronged spear called a trident

and is one of the most important gods

in the Greek pantheon.

Poseidon reigns over all rivers and seas,

leaving Zeus to rule the heavens and Hades

leaving Zeus to rule the heavens and Hades

the underworld.

His bad temper generates storms and floods.

With a strike of his trident, he sets off earthquakes.

Superstitious sailors make offerings of animals to

appease Poseidon's wrath before setting out to sea.

Dora investigates exactly how important the port

of Helike is in the ancient world.

of Helike is in the ancient world.

In recent excavations, the team unearths over

a hundred coins.

Almost all of them are not minted in Helike.

NARRATOR: Coins from visitors far

and wide reveal Helike's widespread importance.

It's the major stop off point for

ships traveling along the Gulf of Corinth.

NARRATOR: This traffic and trade allows Helike's stature to

increase ever further.

In its golden age,

Helike leads an alliance of 12 city-states

in the Achaea region of ancient Greece.

The city plays a leading role in

Homer's epic story of the siege of Troy.

Helike's cultural influence

spreads across the Mediterranean,

as it establishes colonies in Italy and Asia Minor.

Helike's sanctuary of Poseidon attracts pilgrims from far

and wide,

spreading the city's fame across the ancient world.

However,

Helike's high status is unstable.

Ioannis Koukouvelas

believes there's a second reason

Helike's citizens choose to worship Poseidon.

The bad-tempered god of the sea has another name,

The bad-tempered god of the sea has another name,

the earth shaker.

NARRATOR: Helike prospers thanks

to its links to Poseidon, the sea god,

but as god of earthquakes, he brings destruction.

but as god of earthquakes, he brings destruction.

What sequence of events causes

the thriving city to vanish overnight

in 373 BCE,

and is there any escape for Helike's residents?

NARRATOR: The ancient city of Helike

disappears in 373 BCE.

in the hills above its buried ruins,

Ioannis Koukouvelas searches for the cause

of the city's disappearance.

The exposed rock reveals clues

The exposed rock reveals clues

to the area's recent geological past.

There are several steps called offsets

where layers of sediment suddenly drop downwards.

NARRATOR: The offsets reveal this coast is prone

to one of nature's most destructive forces,

earthquakes.

NARRATOR: The larger the offset, the greater the tremor that

causes it.

NARRATOR: One of these large offsets matches

the strong earthquake that spells disaster for Helike.

On a winter's night of 373 BCE,

an earthquake of a magnitude above

6 on the Richter scale strikes Helike.

6 on the Richter scale strikes Helike.

According to ancient eyewitnesses,

immense columns of flames erupt from cracks in

the ground -- their light shines across the city.

Tremors rock the buildings, reducing them to rubble.

Then, astonishingly, the whole of Helike sinks into the ground.

Can this terrifying tale of

the earth engulfing entire buildings be true?

the earth engulfing entire buildings be true?

Christian Malaga Chuquitaype of Imperial College

London investigates.

Is it possible for full buildings

or structures to be swallowed by the earth?

So what I'm going to do here is offer you

a demonstration of what happens when an earthquake hits

saturated soil.

NARRATOR: This high-tech shaking table replicates what happens

when an earthquake strikes -- like many coastal cities,

Helike is built on sandy soil just above the water level.

Helike is built on sandy soil just above the water level.

I'm just, um, mixing,

allowing the water to go deeper.

NARRATOR: Christian places model structures into

the tank, which contains sand saturated with water.

CHRISTIAN: The soil at this stage, although it has water,

it's able to sustain the weight of the structure

and keep it in place.

NARRATOR: Ancient Helike's buildings are well supported,

but the saturated ground is vulnerable to seismic activity.

but the saturated ground is vulnerable to seismic activity.

Christian's table replicates an earthquake's

rapid back and forth shaking.

So it's going now.

[rapid shaking noises]

NARRATOR: The earthquake first knocks buildings over.

Then they start to sink into the ground.

What happens is that the water pressure inside

the sand starts to increase, and at some point,

the sand starts to increase, and at some point,

it breaks all the capacity that the sand has to sustain

the structures on top of it -- the sand is

unable to sustain the load of the buildings.

NARRATOR: This phenomenon is called soil liquefaction.

The tremors cause underground water

to overcome the sand's supportive power.

The science shows model buildings will partially,

but not completely, disappear into once solid ground.

but not completely, disappear into once solid ground.

Five days before the disaster, animals flee the city,

perhaps sensing tremors in the ground beneath their feet.

On the fateful night the earthquake rocks Helike,

soil liquefaction sucks buildings into the ground.

Few citizens can flee the annihilation.

Ten Spartan ships anchored in Helike's harbor

Ten Spartan ships anchored in Helike's harbor

are dragged down into the ocean.

A 2,000-strong rescue team from neighboring

cities searches for survivors, to no avail.

Christian's first demonstration shows

buildings can be partially swallowed by sandy soil.

But to test whether liquefaction can consume

But to test whether liquefaction can consume

the entire city, as ancient sources claim,

he sets the shaking table to

the equivalent of 8 on the Richter scale.

This matches some of the strongest earthquakes

ever recorded.

I'll start. Yep.

[loud rattling noises]

NARRATOR: The buildings begin to sink.

But as they do, the sand beneath compresses.

But as they do, the sand beneath compresses.

Eventually, the ground firms up

enough to bear the structure's weight.

You can see that the building here, it's not fully sinked.

Even if you have a very, very strong shaking,

I would expect buildings to tilt, buildings to break,

and some parts of them to be swallowed,

but the idea of whole buildings

just completely disappearing into the ground

is probably a bit of a literary freedom.

is probably a bit of a literary freedom.

NARRATOR: Liquefaction very likely

plays a part in Helike's fate.

But liquefaction alone can't cause an entire city

to disappear.

What really wipes out Helike?

Will evidence on the ground

match the extraordinary ancient accounts?

NARRATOR: In 373 BCE, Helike,

one of the great cities of ancient Greece, disappears.

A team of scientists seek to

piece together its fatal final days.

After the earthquake,

ancient texts report a rapidly rising sea.

Then they state water completely submerges the city.

Then they state water completely submerges the city.

Ioannis Koukouvelas

suspects the accounts describe another natural phenomenon.

NARRATOR: When Dora's team examines Helike's buried ruins,

they spot something unusual about the settlement.

A set of stones lies scattered at ground level.

The stones once formed the lower section of a wall of

a house -- a powerful blow has pushed it over.

a house -- a powerful blow has pushed it over.

This could come from a natural phenomenon.

Could this be evidence that a tsunami

provides the knockout blow that seals Helike's fate?

Ioannis Karmpadakis models Earth's biggest waves

Ioannis Karmpadakis models Earth's biggest waves

in these 75-foot-long tanks at Imperial College, London.

Ioannis wants to find out whether

a tsunami could cause Helike's pattern of destruction.

A tsunami starts when an underwater earthquake

A tsunami starts when an underwater earthquake

or landslide stirs a large volume of water.

NARRATOR: In deep water, the wave is small.

But as the tsunami squeezes into the shallows, it changes.

NARRATOR: The initial tsunami isn't enough to push down walls.

There is a secondary phenomenon at play.

Ioannis adds loose material to represent

debris created by the earthquake.

The incoming wave uproots this debris.

NARRATOR: The wave retreats, but it's now loaded with

debris, ready to smash anything in its way.

NARRATOR: The experiment explains why the destroyed

NARRATOR: The experiment explains why the destroyed

wall falls towards rather than away from the incoming sea

and proves it is very possible a tsunami strikes Helike.

Now, Ioannis investigates if a tsunami can

be big enough to engulf the entire city,

as the ancient texts describe.

The geological evidence suggests Helike's earthquake

peaks at around 6.5 on the Richter scale.

peaks at around 6.5 on the Richter scale.

NARRATOR: The waves in the previous experiment

match massive earthquakes,

around magnitude 8 on the Richter scale.

NARRATOR: A smaller earthquake reduces the height of the wave

and therefore the distance the water can reach inland.

and therefore the distance the water can reach inland.

Enough to damage some buildings

but not to swamp the entire city,

as the ancient texts describe.

NARRATOR: Rather than a single devastating wave,

the evidence shows the ancient accounts

miss or misinterpret a more complex chain of events.

The earthquake creates a 6-foot-high tsunami

that wipes out the boats in Helike's Harbor.

As the destructive wave washes inland,

it destroys the walls of some buildings.

The tremors also break a natural

river dam in the mountains behind Helike,

releasing millions of gallons of fresh water

onto sections of the city.

Part of Helike's coastal plain drops several feet.

This allows seawater to submerge all

but the tallest buildings and trees.

Dora Katsonopoulou's team

Dora Katsonopoulou's team

believe the influx of fresh and saltwater creates

the lagoon that smothers most of Helike, until it too

eventually disappears.

At her latest dig site,

she hunts for clues to how much of Helike survives.

Okay. Good.

NARRATOR: These ruins lie just a third of a mile

from flooded parts of the ancient city.

They date to a period of reconstruction after

the earthquake.

NARRATOR: Ancient workers dye cloth in these basins.

NARRATOR: This site reveals not all of Helike

and its people are overwhelmed by the disaster.

NARRATOR: The lagoon drowns the earthquake-damaged remains

of Helike's Poseidon statue temple and sacred sanctuary.

But other parts escape.

But other parts escape.

NARRATOR: The mystery of

Helike's fatal moment is solved.

Ancient writers exaggerate a moderate earthquake that

drags Helike's most famous monuments

into the depths of a lagoon,

into the depths of a lagoon,

where they remained to astound fishermen for 500 years.

On the outskirts of Helike,

life resumes soon after the disaster.

One final question remains.

Why does this lost city's fate so

closely mirror the legendary tale of Atlantis?

Could the life story of Atlantis's creator provide

some clues?

NARRATOR: In 373 BCE, an earthquake triggers a cascade

of events that submerge the ancient city of Helike.

The city's tragic end echoes the story of

the most famous lost kingdom of all, Atlantis.

JASMINE: The story of Atlantis is something we all heard

as children -- it's this story that captivates us,

as children -- it's this story that captivates us,

because not only is it a lost civilization

that we want to uncover,

but it's also a civilization that's submerged,

destroyed by tsunami and earthquake.

NARRATOR: Jasmine Elmer researches real life origins

of ancient myths.

She investigates whether Helike could be

the inspiration for the great lost city of legend.

Her research starts with ancient texts.

Her research starts with ancient texts.

Around 360 BCE, Greek philosopher Plato

describes the lost land in two works --

the Timaeus and the Critias.

So this is where we first see

the actual words in the Greek, [speaking Greek],

which means the island of Atlantis.

It's the first time that Plato actually mentions Atlantis.

NARRATOR: Plato's Atlantis story is an allegory,

NARRATOR: Plato's Atlantis story is an allegory,

a fable he concocts to teach a moral lesson.

However, actual locations and events may allow

him to inject some realism to the tale.

I think it's a really good exploration to consider all

those different points of view and the --

and the contemporary historical events that are

going on to see if there is an inspiration there for Plato.

NARRATOR: The first clue Helike could inspire Atlantis is that

citizens of both places are devoted to the same god.

citizens of both places are devoted to the same god.

JASMINE: And in the center of the island is the temple

to Poseidon.

And the cult of Poseidon is obviously

a really important part of Atlantean culture.

And that's really similar in some ways to Helike, because

the cult of Poseidon there

was dominant and well known across the Greek world.

NARRATOR: Plato writes the gods destroy Atlantis as

a punishment for the arrogance of its citizens.

This tale of retribution echoes a story told about Helike.

Some citizens from Helike's colony in Asia Minor traveled

back to their homeland on the advice of an oracle.

They make a sacrifice to Poseidon

and reveal a plan to take back

sacred relics that belong to their forefathers.

The inhabitants of Helike are

affronted and murder their visitors.

affronted and murder their visitors.

Poseidon is angered by this outrage.

He punishes Helike and its impious citizens with

a cataclysmic earthquake and tsunami.

The connections between Helike and Atlantis are clear.

Both worship Poseidon.

Both are destroyed and then disappear.

There was an earthquake, there was a tsunami,

there was a flood, and also there is this sort of odd

description of sinking into the earth

in the same way that you get a kind of

liquefaction that's going on as part of the Helike disaster.

NARRATOR: The final clue that Plato has Helike in

mind is when he writes the legend of Atlantis.

Helike is the disaster that happens only

about 15 years before he writes his dialogues.

So it kind of makes sense that this is an event,

a contemporary event that is happening,

it would have been a very well known disaster.

It makes sense that Plato would perhaps have knowledge of that.

NARRATOR: Jasmine believes it's possible

Plato recycles what he hears of Helike

to bring to life his own disaster story.

In the long search for Atlantis,

the trail strongly leads towards one real life lost city.

After a decades-long quest,

After a decades-long quest,

the story of Helike can finally be written.

One of the great ports of ancient Greece,

it rises, thanks to its Poseidon cult, to dominate

the Gulf of Corinth.

The city falls in the earthquake of 373 BCE.

Its sanctuary and statue disappear underwater for

five centuries,

then vanish completely for almost two millennia

until Helike's rediscovery today.