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
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
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.
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?
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.
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.
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,
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,
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.
She re-examines the ancient eyewitness's description.
[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?
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.
[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 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.
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.
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.
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
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.
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
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.
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 earth shaker.
NARRATOR: Helike prospers thanks
to its links to Poseidon, the sea god,
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
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.
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?
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.
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.
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,
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.
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
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
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.
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.
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.
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.
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
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
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
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.
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.
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
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.
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,
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,
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.
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,
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.
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.
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,
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.