Original subtitles

begin hearing strange noises.

Could this be some kind of sinister continuation

of spy games between the two countries?

- The goal was to frighten, demoralize,

and force their enemy to abandon their post.

[narrator] A bizarre discovery in a remote Australian island

territory near Antarctica leaves scientists puzzled.

There's a pile of stones near the shoreline

that appears entirely out of place.

Clearly somebody built this thing here

in the middle of nowhere, but why?

[narrator] Objects in the waters off the Dry Tortugas Islands

have links to a dark history.

Just below the waves is this strange series of dots.

So what are these things?

♪ ♪

[narrator] Isolated, scarce on resources, islands are worlds

unto themselves.

Bizarre creatures, ancient gods, and haunting ruins.

Baffling murders and deadly spirits.

What will be discovered on Earth's mysterious islands?

♪ ♪

[thunder rumbling]

[narrator] The Republic of Cuba is the largest Caribbean island

with an area of over 42,000 square miles.

It connects to a chain of islands called

the Greater Antilles, which were formed

millions of years ago.

Today, Cuba has a population of over 11 million

made up of indigenous, African, and European descendants.

This mixed population is a result of its colonization

by Spain that began shortly after their first contact

in 1492 and Spain's subsequent involvement

in the slave trade.

Cuba claimed its independence from Spain

and later America by the early 1900s,

but struggled to find its path forward

in the decades that followed until Fidel Castro led a

rebellion to victory in 1959.

Depending on your point of view,

Castro can be viewed as either a ruthless communist dictator

or a heralded anti-American champion of social justice.

He led the country until 2008 when he turned leadership

over to his brother and ultimately passed in 2016.

Due to the clashing of capitalist and socialist ideals,

American-Cuban relations have been strained

since Castro's revolution.

In 1962, tensions peaked between the two countries

during the Cuban Missile Crisis as the world was brought to

the brink of Nuclear war.

[narrator] The crisis arose after American spy planes

discovered Soviet nuclear missiles on Cuba.

Ultimately, diplomacy prevailed and conflict between the

two Cold War superpowers was averted.

President Obama lifted long-held travel bans

to and from Cuba, engaged in prisoner swaps,

and finally in 2015, the two countries restored

diplomatic relations.

However, late in 2016, shortly after

President Trump was sworn in, something changed.

An employee at the American Embassy in Havana

reports hearing strange noises outside their house,

an annoying, near constant, even mechanical sound

that they can't escape.

[mechanical sounds]

They try closing all their windows and doors

and even blast their TV to drown it out,

but nothing works.

And they're not alone either.

Their neighbor, who's also a co-worker,

is hearing things too.

What's going on?

Perhaps it's something natural from the environment.

If you've ever been caught in the midst of a cicada

or cricket mating season, you know what an audio

assault it can be.

[cicada noises]

Could insects be the source of the sound?

[Amma Wakefield] Male cicadas are among the loudest insects

on the planet, transmitting their sound at 100 decibels

and at a frequency of 4.3 kilohertz.

And that's just one male, not even an entire

field of them.

[cicada buzzing]

Cicada calls are so loud, they can be heard up to

a mile and a half away.

[narrator] Unlike grasshoppers that rub

their back legs together,

cicadas produce sound through the vibration

of a pair of drum-like structures called tymbals

found on their backs behind their wings.

Cicadas can be found on every continent in the world,

except Antarctica, with nearly 1,000 species

throughout the Americas, including Cuba.

So could they be making the noise?

[narrator] As the noise complaints continue,

another staff member of the embassy reports

that he too is hearing the sound.

It's noted that the sound materializes

predominantly at night, not only in homes, but hotels too.

And all the reports are within a few miles radius

of the U.S. embassy.

The noise is described like grinding metal,

a loud ringing, and even the effect created

when you drive down the highway with one window open.

Many contradicting descriptions.

And people at the embassy are reporting headaches,

disorientation, memory and hearing loss

due to the ongoing noise pollution.

It's getting serious.

But no matter how many cicadas or crickets

or some combination thereof were present,

they would not be able to cause actual hearing loss

unless one was held right to your ear

for an extended period of time.

So what else could be at play here?

Adding a layer of intrigue to the situation,

the first people to come forward after hearing the sound

not only work for the embassy, but are also CIA agents.

Could this be some kind of sinister continuation

of spy games between the two countries?

[narrator] Sound has been used as a weapon,

even by the U.S. themselves.

During the Vietnam War, the U.S. military employed a

top secret psychological warfare campaign called

Operation Wandering Soul throughout Vietnam.

Operation Wandering Soul played audio recordings

of wailing, sobbing and screaming in Vietnamese

on the battlefield using portable speakers.

[various distorted noises]

The goal was to frighten, demoralize

and force their enemy to abandon their post.

But results were mixed and hard to track.

[Sarah Klassen] And eerily close to the American embassy in

Havana is Guantanamo Bay, the site of an infamous

American naval base and detention center,

where there have been many reports of a practice

known as song torture, in which pop music

is used against prisoners.

But in both cases, the subject matter of the audio

was the weapon, whether played on repeat

or at extreme levels.

However, there is a more recent piece of technology

that uses audio differently.

[narrator] The weapon is a long range audio device or LRAD.

When used to communicate, it offers loud

and clear messaging, but when employed as a weapon,

it produces an irritating and potentially painful noise.

[high pitched alarm noise]

The creators of the tech liken its amplification of sound

to what a magnifying glass can do with light.

And really anything over 75 decibels

can be damaging to your hearing.

[high pitched alarm noise]

[Amma Wakefield] But the LRAD can emit sound at 150 decibels.

That is dangerously loud.

Human exposure to sound at 150 decibels

causes vibrations that kill the tiny hairs in our ears

that allow us to hear.

And they don't grow back.

[narrator] LRAD technology was developed in the U.S. in 2000

to help enforce safe zones around military vehicles.

When it was used on civilian protesters in 2020,

many were left dizzy, disoriented,

and some even reported permanent hearing loss after exposure.

[high pitched alarm noise]

So the tech had been around for more than 15 years

when the situation with the Americans,

now known as the Havana Syndrome, began.

And the symptoms experienced by some of the embassy staffers

are similar to the effects of these weapons.

[narrator] As concerns grow and the number

of affected staffers rises, 24 employees and diplomats

from the American embassy in Havana

are evacuated for testing, some of whom

were mistakenly believed to show signs of brain injury.

If it were a weapon like the LRAD,

in order to penetrate walls and structures,

it would likely be so loud it would

be impossible to hide from the greater Havana community.

But there have been no such reports that we know of.

And these complaints seem to be coming

from one group, foreign diplomats and CIA agents.

[Sarah Klassen] Other experts interpret the sound

as intermodulation disorder.

[traffic noises]

An auditory phenomenon that

can occur when frequencies from everyday electrical items

are crossed with surveillance equipment.

But if it were some kind of accidental distortion,

how is it so widespread?

[narrator] After a lengthy investigation,

the FBI conclude that no sonic event could

have resulted in the physical symptoms reported.

And ultimately, no actual brain injury

could be attributed to Havana Syndrome itself.

There is actually another theory that could apply here.

It might be a functional neurological disorder

or conversion disorder, where a person experiences

real physical or sensory problems

with no underlying neurological or physical cause.

It's the conversion of emotional stress into physical reaction.

Moving to a new country as a foreign diplomat,

it would be stressful on its own.

But being an American diplomat or CIA agent assigned

to the Cuban embassy, it's the perfect cocktail

for a conversion disorder, or in this case, mass hysteria.

[narrator] Mass hysteria is identified when

there is a rapid spread of illness or symptoms

among members of a connected social group,

but there is no corresponding organic or physical origin

for those shared experiences.

This could also explain how the noises and subsequent symptoms

seem to be experienced by one specific social group,

in this case, foreign diplomats, CIA agents, and their families.

When reports of the cases in Havana hit mainstream media,

they had fueled the fire and whip up tensions

with words like "victim" and "attack,"

reigniting decades of unsettled Cold War history

between the two countries.

[narrator] In the end, over 80 embassy staff and their families

report the noise and symptoms.

Even Canadian diplomats and their families

stationed in Havana report strange noises

and concussion-like symptoms as well.

As word of Havana Syndrome spread

within the intelligence community and mainstream media,

it seems diplomats all over the world, from China, Russia,

Taiwan, Colombia, Germany, and Poland,

all began reporting similar symptoms.

Ultimately, it affected more than 1,000 government employees

over several years across various posts.

Cases of mass hysteria are particularly interesting

when we look at their collective symptoms and causes.

They are not fixed over time, but appear to change with

the culture at the moment.

A mass event was born from the hysteria

of the Salem witch trials, when a group of young women

testifying about witches began screaming and

writhing in court.

It was so compelling, it led to the conviction

and hanging of 19 women and men.

[narrator] After Germany's use of mustard gas in World War I,

a form of mass hysteria was triggered

when groups of people thought they were

smelling gas in Britain.

And this happened again in a town in Illinois

after the release of World War II propaganda

about the enemy gassing the innocent.

The town became convinced that they too were being gassed.

Outbreaks of mass hysteria are prone to areas

where people are forced together under pressure.

Schools, factories, military bases,

all are potential hotspots.

Embassies where a large percentage of employees

are undercover and former military

would be another prime example.

Given the context of the time in which

Havana Syndrome appeared, a world of political mistrust

and massive technological advancements

and espionage and war, and let's not forget the impact

of the extraordinary levels of noise pollution

we live with today, it makes sense that this

could be another example of a conversion disorder

like mass hysteria.

[Alison Leonard] But there are many who are not convinced.

Even though the FBI and intelligence community

concluded that there is no evidence

of adversarial weapons at play, they did not provide an answer

as to what the root cause was.

[Amma Wakefield] Ultimately, in response to all the chaos and

suspicion, the US ejected 15 Cuban diplomats from Washington

and shut down their embassy again in 2017.

Trump even returned Cuba to the State Department's list

of state-sponsored terrorists.

[narrator] To this day, there are still departments

within the US government searching for answers

about the sound initially reported in Havana.

But when it comes to Havana Syndrome,

what's real and what is not may be hard to come by.

In January of 2023, the US embassy fully reopened,

not only continuing diplomatic relations,

but they began to allow American travelers

who meet specific criteria back to Cuba

to enjoy what this wonderful island

and its people have to offer.

Just over a thousand miles north of Antarctica,

in the middle of the South Indian Ocean,

sits Heard Island, one of the most remote

and foreboding places on the planet.

Heard is roughly 142 square miles in total area

and is covered by glaciers, some of which contain ice

that's almost 500 feet thick.

Volcanic activity has created iron-rich water

around Heard Island, resulting in high

concentrations of phytoplankton, the building blocks of

the ocean's food chain.

Because of this, the island is home

to an abundance of wildlife.

[narrator] In 2016, a team of scientists is conducting

research in the northwestern part of Heard Island

near an inlet called Corinthian Bay

when they come across a bizarre sight.

There's a pile of stones near the shoreline

that appears entirely out of place in this environment.

Looking at it, there's just no way

that these stones ended up here naturally.

So someone had to have put them here in this manner.

What is it?

[Amma Wakefield] It's a wall that stands almost

five feet tall, though much of it seems to have fallen over,

likely due to seals.

What is left appears to be the remains of a house

or structure of some kind.

Perhaps it's a bunker or a fortification of some kind.

But that doesn't make much sense.

There's nothing on the island to defend.

This is not highly sought-after territory.

[narrator] Continuing to explore the area, the team makes another

surprising discovery not far from the

mysterious pile of stones.

There are remnants of what looks like

an old structure of some kind.

It's falling in on itself and there's wooden

debris scattered around.

Clearly, somebody built this thing here

in the middle of nowhere, but who would have lived

on Heard Island and why?

- The next closest inhabited places

are the Kerguelen Islands, nearly 300 miles away,

and Mawson Station, Antarctica, over 1,000 miles away.

Both host permanent research bases.

Perhaps Heard Island was a base for scientific research as well.

[narrator] Expanding the investigation, the team comes

across another bewildering sight.

There are rusting cast iron pots littered around.

This isn't your average cooking or camping equipment, though.

These are massive cauldrons, about four feet in diameter,

and weighing around one ton.

Given the extensive rust, you can assume that these things

have been lying around for a long time.

They could have something to do with the whaling industry.

In the late 19th and early 20th century,

rudimentary settlements sprung up in remote places

all over this part of the world.

Whales were hunted using a combination

of large and small boats, harpooned and then

hauled back to the camps where their blubber was

cooked and rendered into oil,

a highly sought-after commodity at the time.

[narrator] Just off the northern tip of the Antarctic Peninsula

lies Deception Island, part of the South Shetland chain,

and it's an active volcano.

There are tanks on Deception Island

that look kind of similar to the Heard Island pots.

We know that there was a whaling station

on Deception Island in the early 20th century,

and these tanks were used to process whale blubber.

Is that what was happening on Heard Island too?

But the tanks on Deception Island

are way bigger than the pots on Heard.

It has to be something else.

Seals were widely hunted, not only for their

meat and pelts, but for their blubber,

which was processed into oil, used for cooking,

as a lubricant, and lamp fuel.

[narrator] Around 280 miles northwest of Heard Island

are the Kerguelen Islands, a French overseas territory

discovered in 1772.

Similar iron pots to the ones on Heard Island

can be found scattered about the coastline

of the Kerguelens.

Based on historical records, we know that there was

sealing activity here beginning as early

as the late 1700s.

So if those pots were used for sealing,

perhaps the pots discovered on Heard Island

were used to process seal blubber too.

[narrator] Heard Island was first sighted by

the British sealer Peter Kemp from aboard

the ship Magnet in November 1833,

but he never officially reported the sighting.

So when American Captain John Heard

spotted the landmass in 1853, the island was named after him.

Heard's find made newspapers around the world,

and it wasn't long before some enterprising sealers

showed up, hoping to exploit the island's robust

seal population.

The first landing was made in March of 1855

by another American, Captain Darwin Rogers.

On that first trip, he returned to the US

with around 400 barrels of elephant seal oil.

More ships were then dispatched to Heard,

and the island's sealing era began in earnest.

[narrator] For roughly the next 25 years, hardy crews of men

lived and worked in brutal conditions on Heard Island's

unforgiving shores.

They would have been dropped off for months at a time,

left to hunt the seals and then process the blubber into oil.

It must have been a harsh existence.

They lived in makeshift shelters dug into the ground

or crude stone huts, like the pile of rocks first

discovered by the shore.

[James Ellis] By the 1880s, seal populations around the island

had dwindled significantly, and the market for

seal oil was collapsing due to the development

of cheaper alternatives.

So Heard Island was abandoned, but sealers never constructed

any permanent structures while they used the island.

So who could have built the wooden building?

[narrator] Looking for answers, the team continues

to investigate a strange object to the rear of the structure.

It looks like a rusted old tank of some kind

propped up on a wooden platform.

There's a pipe extending from one end

and an inscription above the pipe.

The inscription identifies it as Furfey's Farm Water Cart,

manufactured by J. Furfey & Sons in Shepparton, Australia.

Over the name, it says,

"Born about 1880, still going strong 1942."

This means that there was a presence on Heard Island

after 1942, over 50 years after the sealers abandoned it.

So who was here?

[narrator] A deep dive into the archives of Heard Island

turns up a book entitled

"Fourteen Men," written by William Arthur Scholes

and published in 1949.

The book outlines the Australian National Antarctic

Research Expedition to Heard Island in 1947.

Fourteen men established a research station

and eventually around 35 buildings were erected,

the ruins of which can still be seen today.

Their research was mostly in the meteorological field,

but other studies were also conducted

between 1948 and 1954.

Ultimately, the station was closed in 1955

when that expedition established a permanent base

on the Antarctic mainland.

[James Ellis] Today, exploring Heard Island is a bit like

walking through a time capsule from the early sealing activity

right through to the research years.

There's remnants of an engine room with heavy machinery,

storage units, and even a church.

All eerily left to decay on this desolate island

in the middle of nowhere.

[narrator] In recent years, efforts to clean up Heard Island

have been successful in removing some of the debris left behind,

but it's a daunting task requiring time and money.

For now, the remnants of days gone by

that litter the shores of this rugged land of fire and ice

provide a vivid snapshot of the island's fascinating history.

♪ ♪

The Shetland Islands are a remote, rugged archipelago

in the North Sea, roughly 130 miles off

the northeast coast of mainland Scotland.

At the Shetland's most easterly point are the Out Skerries,

a group of three small islands and many tiny islets.

The word "Skerry" means a rock in the sea

or small rocky island.

And it's usually presumed that the "out" in the name

refers to the island's remote location.

But "out" is actually the Old Norse word for "east."

Only two of the Out Skerries are inhabited

with a total population between them

of fewer than 80 people.

This is a sleepy, quiet place without much going on.

With that said, the scenery is spectacular.

[narrator] A young couple is out for a scenic stroll

along the coastline of the Out Skerries

when they notice something peculiar washed up on the shore.

It's a black tablet measuring around 12 by 14 inches

with slightly rounded edges.

It kind of looks like a chopping board

that you'd find in someone's kitchen, but thicker.

What is this thing?

[narrator] The couple approaches the mysterious object

and picks it up for a closer look.

It's surprisingly light, only about three pounds,

and feels a bit like rubber.

So obviously it's not a natural stone formation.

The surface is covered in slimy algae,

meaning that it's probably been in the water

for quite some time.

Now here's where things get a little strange.

They turn the tablet over, and there's an inscription

stamped on the underside that reads "Tjipetir"?

"Tjipetir"? What the heck is "Tjipetir"?

Is that a place?

Is that someone's name?

[narrator] S o-called Tjipetir blocks have been washing up

on the shores of the United Kingdom

and Northern Europe for several years.

They've been discovered on the coastlines

everywhere from Southeastern Norway to Northwestern Spain.

Thousands of these things have been found,

and the fact that they've come ashore

across such a wide area is a bit perplexing.

If they all came from the same place, wherever that is,

it stands to reason that they would end up

in the same place.

But I guess the Atlantic Ocean has a mind of its own.

[narrator] Searching for answers, the couple turns

to the place where many amateur sleuths

do their investigating, the internet.

A quick search didn't turn up any information on the blocks,

only that Tjipetir was the name of a small village in Indonesia.

So why are rubber-like blocks stamped

with the name of an Indonesian village

over 7,000 miles away, washing up on beaches all over Europe?

The obvious answer would be that that's where they came from.

Stamping the name of a place or a company name

that made certain products was pretty common

in the 19th and 20th centuries.

Think of brickmakers, for example.

They would put their name on products

that they would send all over the world,

and it would be a way of advertising

everywhere they went.

It's pretty ingenious, really.

So we can assume that these blocks come from Tjipetir,

but that still doesn't explain what they are

or how they keep ending up on European shores.

It seems highly unlikely that they simply floated

halfway around the world from Indonesia.

There's a photograph that appears to be

from the early 1900s showing a young boy

standing next to a pile of the blocks

on what looks like a farm or plantation.

And it turns out the name of the plantation

is the same as the nearby village, Tjipetir.

They cultivated a tree called pallacrium gutta,

the sap of which produces a rubber-like substance

called gutta percha that was the de facto

precursor to plastic.

[Dan Riskin] The process was refined over the years.

In the early days, the trees were felled

to extract the gutta percha out of them.

But later on, people came up with more sustainable processes

like squishing the tree's leaves with boulders.

That way you could get the gutta percha out,

mold it into blocks, harden it, and then stamp it with

the facility's name without killing the tree.

[narrator] Gutta percha emerged as a popular alternative

to rubber in the middle of the 19th century

and was used to make everything from golf balls to shoe soles.

One of the strengths of gutta percha

is that it's water-resistant, whereas rubber degrades

when it's submerged for extended periods of time.

Because of this, gutta percha was used extensively

to insulate underwater telegraph cables.

- The first transatlantic cable was laid in 1857,

spanning roughly 1,800 miles between

Valencia Island, Ireland, and Harts Content,

Newfoundland, Canada.

The cable weighed around 2,000 tons,

250 of which was gutta percha.

It's estimated that 200 trees would have been required

for every mile of cable.

Gutta percha became somewhat obsolete

by the mid-20th century with the invention of

polyethylene plastics.

But even to this day, it's still used for a few products,

things like sealing wax and filling material

for dental procedures.

The factory in Tjipetir no longer stamp their name

in this manner on the slabs.

So if that's the case, then the blocks washing up

on shore must be pretty old.

Where are they coming from?

[narrator] One of the most popular online theories

surrounding the mystery of theTjipetir blocks

is that they are emerging from a shipwreck,

and not just any shipwreck.

[Dan Riskin] Name a shipwreck.

Exactly, the Titanic.

The timeline fits.

That ship sank in 1912, right around the time that

the Tjipetir factory was in full swing.

And according to one explorer who used a robot

to investigate that ship's holds,

they say they saw objects quite difficult to identify

that resembled slabs of gum.

But the Titanic went down 400 miles

off the coast of Newfoundland after traveling over

2,000 miles from England.

How could gutter percha blocks from that far away

end up on European shorelines?

It's quite possible currents, wind,

and what's called North Atlantic drift

could very well have carried the blocks across the ocean.

And given how far apart they were found,

it actually makes more sense that they traveled

a long distance because the further a

cluster of objects floats, the more widely

dispersed they become.

[Sarah Klassen] Considering how highly scrutinized the wreck is,

surely somebody would have noticed

that it was spitting out slabs of gutter percha.

My guess is the Tjipetir blocks

are probably not coming from the Titanic,

but there are other possibilities.

[narrator] On May 31st, 1917, the Miyazaki Maru,

a Japanese ocean liner sailing from Yokohama to London,

was sunk by a German submarine 150 miles west

of the Scilly Islands off England's southwestern coast.

The Miyazaki Maru was a pretty substantial ship,

over eight and a half tons and almost 465 feet long.

She was carrying passengers and cargo

under the escort of Allied ships when a U-boat attacked

with torpedoes.

The ship was lost and eight people perished.

[James Ellis] It's believed that sometime before the blocks

started washing up on European shores,

salvage work was being done on the Miyazaki Maru,

and they may have pulled them out of the ship's hull.

- But here's the thing, people reported finding blocks

before the salvage work is thought to have begun.

One man claimed that he found a block

more than 30 years ago and used it as a chopping board

to gut fish on his boat.

- Maybe there's more than one shipwreck

releasing the blocks into the water,

or some of them fell off a ship 100 years ago

and have been floating around ever since.

Who knows?

The oceans move in mysterious ways.

[narrator] British authorities looked into the matter

and support the theory that at least

some of theTjipetir blocks probably came from

the Miyazaki Maru.

Maybe in another 100 years, they'll still be washing ashore

in places like the Out Skerry Islands.

The Dry Tortugas are a cluster of seven small islands

that lie around 70 miles west of Key West, Florida.

They sit at the mouth of the Gulf of Mexico.

This archipelago was first documented by Europeans

in 1513 when Ponce de Leon visited

and noted over 100 sea turtles on the island,

hence the name Tortugas, which means turtle in Spanish.

The word dry was added once they learned

there was no fresh water to be found there.

These days, there are no permanent residents

on the island beyond National Park staff and their families.

However, these seven rugged sandy rocks

jutting up from the sea have a long and mysterious history.

[narrator] In 2016, Josh Marano, a maritime archaeologist,

is making his way from Key West to the park via seaplane

when, approaching Garden Key,

he notices something unusual in the water.

Just below the waves is this strange series of dots.

Now, this area's rocky, but these dots appear to

be at regular intervals, all about the same

distance below the surface.

So what are these things?

The Gulf of Mexico is home to a number of

important coral reefs, and Florida is actually the

only continental US state with 350 miles of reef

formation near its shores.

So perhaps there's some kind of coral growth.

[narrator] The warm waters near the Florida Keys reefs

provide a flourishing habitat of biodiversity

for marine life.

Most areas of the Florida Gulf have been made protected areas,

including the Dry Tortugas National Park.

The Dry Tortugas are home to the third largest

barrier reef in the world.

The reefs of the Dry Tortugas have been growing

for nearly 12,000 years.

They can be more than 50 feet thick in some areas,

and there are more than 50 different species of coral.

Coral is a pretty good first guess

about what those dots are, but the pattern of them just

doesn't quite seem right.

[narrator] Marano notices that the dots appear

to fall into a linear pattern, forming a shape similar

to that of a capital L.

[Anthony Cantor] The pattern is clearly manmade,

and they share a similarity to something close by.

While no one really lives on the Dry Tortugas today,

Garden Key, the second largest of the Dry Tortugas islands,

is home to a fort.

[narrator] Fort Jefferson is a military fortress from the mid 1800s.

It's a massive hexagonal structure

that took 30 years to build, yet was never fully completed.

Even so, set along one of the world's busiest shipping lanes,

it was a rallying point for the US Navy

and a great military asset.

It's the largest brick fort in the entire

Western Hemisphere, and it's actually

outlined by a moat.

Could the strange linear dot seen in the waters to the north

be some kind of extension of the fort?

The wall of the moat mirrors the hexagonal shape of the fort,

and at high tides, they're often submerged.

But the dots don't appear to be made of brick.

They're much darker in color.

That said, there is something else at Fort Jefferson

that they do resemble.

[Anthea Nardi] On both the south and north coast of the key,

there are sets of dots similar to what Marano found

sitting just offshore.

They're very weathered and have been in the

water a long time, but what are they?

[narrator] By the late 1800s, the fort was eventually

abandoned as a military post, but it was still used as a

coaling station for warships.

These are pylons or pilings.

They're slender columns made of wood, concrete, or steel

that are driven deep into the ground.

They can be topped with a cap, like the dots that we're

seeing from the plane.

Pylons are support structures used in areas with

poor soil conditions to support large builds.

In this case, they're remains of massive wharfs

used to load and unload the heavy coal from the ships.

Could this mean that Marano found pylons

that form a large wharf?

The pylons in the water around Fort Jefferson

are positioned in these consecutive rows like a grid.

So you can imagine all of them working together

to reinforce a great big platform

holding all that weight of coal for the ships.

But the dots in the water two miles out from Fort Jefferson

are spaced out in a single line with a right angle turn in it.

Maybe it's a more simple dock like you'd find in

a common harbor?

[narrator] Across the globe in Egypt,

a team of marine archeologists were investigating a remote

section of the Red Sea coast at Wadi al-Jarf when

they discovered something strange in the water.

It too was an L-shaped structure

stretching out into the water and then turning

sharply to the right.

It was proven to be the remains of the wharf

of an ancient harbor.

Maybe these dots are the remains of a dock

or maybe they're navigation markers like buoys.

But to what?

There isn't even an island or key here.

[narrator] Spurred on, Marano assembles a team of explorers

to take to the waters where the pylons were found.

Given the spacing of these pylons,

they do appear to be following the outline of something,

perhaps a foundation for a building of some kind.

What would have been built all the way out here and when?

Through a combination of factors, weather,

water movement, and erosion,

an island can be worn down or washed away

as water levels rise around it.

Given that Dry Tortugas and the Florida Keys

are surrounded by fragile reefs and sand,

they are especially susceptible to these changes.

[narrator] The Gulf Islands are primarily composed

of ancient coral limestone.

Over years of battering by waves,

this porous rock can wear down, resulting in the

reduction of the land area and change in shape

of its coastlines.

People think of erosion as this slow, gradual process,

and that can be true, but erosion can also

happen really quickly, like in the case of

hurricanes and tropical storms that blow through this region.

Those result in flooding, strong currents,

and not to mention wind.

[narrator] Global warming in the Gulf is happening much faster

than in many other regions of the world,

leading to a variety of negative environmental impacts,

such as rising sea levels.

The sea levels in the Gulf region are expected to rise

as much as 18 inches in the next 30 years.

The Dry Tortugas have never been

particularly high above sea level.

Loggerhead Key, the biggest of the islands by area,

is also the highest, and it only sits

10 feet above sea level.

There are actually four additional keys

that were once part of this series of islands

and no longer exist due to rising water levels.

So perhaps the pylons are an indication

that this too was once a large key

that could have supported structures.

[narrator] Taking to the water once more, a member of the team

discovers a strange, oddly-shaped rock with

algae clinging to its surface 10 feet under the water.

The shape is a nearly perfect rectangle.

It's about six feet long, two feet wide,

and it's lying flat in the sediments along the seafloor.

This is clearly not a random hunk of coral, but what is it?

[narrator] The team takes time to carefully examine the shape

by cutting away the seaweed and scrubbing away

the algae and sand to reveal its original form.

It's a large, fallen tombstone,

and after it's cleaned, there's a visible inscription.

It reads, "John Greer, November 5th, 1861."

So who was John Greer, and what was he doing out

here on this strange key?

[narrator] Armed with a name, the team searches

archives near and far, and they discover a wealth

of information about Greer and his connection to

the Dry Tortugas.

Greer was a scaffolder who had helped to build

Fort Jefferson before his death, but if this is true,

why did his grave end up just two miles away on another key?

85% of Garden Key's area is taken up by the fort,

so it makes sense that they would have sought out

more land for things like burials.

The records show that Greer is one of dozens

of men buried here, most of whom were military men,

but that still doesn't explain what the pylons were for.

[narrator] Nautical records and maps dated from the time of

Fort Jefferson's construction referred to a much

larger key at this site, and not just that, but

this mysterious key which featured some

kind of large structure.

It seems that as the fort grew,

exceeding its footprint on Garden Key,

it needed more and more space for additional services,

especially hospitals.

In the late 1800s, with yellow fever tearing

through the country and ultimately this fort,

the military took advantage of nearby keys

to treat, house, and quarantine anyone infected.

And the L-shape of those pylons that were first discovered,

according to the records of the US Marine Hospital Service,

corresponds to the site of a 30-foot by 30-foot foundation

for one of those facilities.

[narrator] But after 150 years of being battered by storms

and some of the most fierce hurricanes on the planet,

the foundation is all that remains.

Given the severity of the yellow fever

outbreak at the time, it makes sense that a

cemetery would be found in the vicinity of a hospital.

However, whether or not John Greer

was a victim of that disease is, as of yet, unknown.

Since the days of the hospital's operation,

repeated storms, hurricanes, and climate change

have resulted in water levels rising,

completely submerging this key for nearly 100 years.

[narrator] 99% of the Dry Tortugas National Park

is already underwater.

For the remaining 1%, explorers in the region

will continue to uncover the many stories and secrets

these historic and beautiful disappearing keys hold.