NOVA

In icy Nordic waters,

a mysterious wreck.

There's nothing else like it.

We've never seen anything else like this archaeologically.

The long-lost warship

of a late medieval king.

It's a statement of power... it's floating propaganda.

Sunk under mysterious circumstances

over 500 years ago.

What secrets does it hold?

How did it come to be here?

What cargo did it contain?

We were jumping up and down

and said, "We have found a figurehead!"

That's great, unbelievable.

Yeah, it's amazing.

Written records of the time

described it as a fearsome vessel.

It was designed to project power.

It was a floating castle.

More powerful than

the Viking ships that preceded it.

How was it built to be so large?

We got some things

we don't understand, frankly.

And could it have been part of

the technological revolution that built

the great ships of exploration

that carried Columbus and others

across the Atlantic and around the world?

Designed for the same types of mission,

built in the same way.

This is our look at what Columbus and his crew

actually experienced on their voyages of exploration.

That's what makes this shipwreck so important.

Because it's, it's a treasure, in fact.

There's only one way to find out...

Excavation time.

If it's the ship

that changed the world.

Right now, on "NOVA."

Stora Ekön.

A small island off the coast of Sweden.

Marine archaeologists Brendan Foley...

Excavation time.

And Johan Rönnby...

along with a team of divers,

have come here to investigate

the crumbling timbers of a ship.

It may not look like much,

but they suspect it may be a rare type of warship.

Large portions of the wreck appear to still be intact.

I can see a ship!

I can see the bow, the stern,

the ribs... I can see a ship.

Visible in the sediment,

several tell-tale items.

There are artifacts emerging.

Saw a nice lead cannonball.

And an oddly carved piece of wood,

possibly the remnant of a gun carriage...

built to hold an early type of cannon.

Its distinctive design suggests that this object

dates back to the late medieval era, 500 years ago,

a time of castles and armored knights

and the first stirrings of the European Renaissance.

It's the period of Michelangelo and Leonardo da Vinci,

and it's this period in European history

where a lot of things are changing.

And yet, ironically, this ship

may have been hiding in plain sight since the 1970s,

when amateur divers

first stumbled across it

without realizing what they'd found.

Fishermen had told that every time

they was fishing at this place,

they got stuck with the equipment.

And they say, "We go down here and look."

And Neesa got down,

and when he come up, he said to me, "I don't know.

Must be some, a wreck."

That in and of itself wasn't unusual...

shipwrecks are common in these waters.

And then archaeologist Niklas Eriksson

found a strange artifact,

and the wreck started to make headlines.

So I was swimming back and forth

and having a look at

the loose timbers that are lying scattered around there.

I found a thick beam.

After removing some sediments,

we came back to the surface

and we were jumping up and down and said,

"We have found a figurehead!"

It was, it was quite amazing.

Centuries ago, this bizarre, intricately carved figurehead

would have been one of the ship's key identifying features.

It's clearly some kind of monster,

similar to the fantastical creatures

that often adorned old Viking ships.

In its jaws, a screaming man.

I think it's, you can see it as part of

the psychological warfare, really, because this is

the first thing you meet when it's coming.

As propaganda goes,

this is pretty powerful stuff.

But the figurehead alone

was not enough to make a positive I.D.

Military historian Ingvar Sjöblom

soon put the clues together.

It was probably a very rich man

that, that could, could have the money to build

a large ship of this size.

Along with other clues gleaned from the wreckage,

the figurehead and gun carriages suggest

that this could be the flagship of a Danish king named Hans.

Over 500 years ago,

the monarch was famous for building a large naval fleet

led by a massive warship known as the Gribshunden...

"the Griffin Dog."

It's the capital ship of King Hans.

It's the aircraft carrier.

It's the ballistic missile submarine.

It's a statement of power... It's floating propaganda.

Now I really understand what's down there.

Four chronicles mention Gribshunden by name,

as does a single eyewitness account,

written by a young nobleman who survived the ship's sinking.

They report that in 1495,

the Griffin Dog came to this island

seeking shelter, before sinking...

...under strange circumstances.

The finds yesterday were

really exciting, quite spectacular,

and I think we're going to have

the same today, so...

Now, Foley and Rönnby

are preparing to uncover this ship's secrets.

The work won't be easy.

Though the wreck is not in deep water,

it's mostly covered in heavy sediment.

Excavating requires a highly skilled support team

and extreme caution.

You'll be told who is the dive leader for that rotation,

and their word is God.

To keep them safe as they work,

dive safety officer Phil Short and his crew

will monitor the divers at all times.

It is a shallow site,

but you can't breathe water at nine meters or 90,

so safety is absolutely paramount.

Their base of operations

is a 30-foot dive boat

hauling up to ten divers and their gear.

We can jump in the water and get to work.

And you can take samples.

A temporary lab back on shore

is set up to process any artifacts they recover.

Their time is limited.

They only have the dive boat

and this team together for 16 days.

Their first objective

is to understand how much of the ship

is still intact beneath the sediment.

We have to excavate further down.

So we have to remove the silt around it

so you can get the whole structure of it.

The first step is to expose the cargo hold,

all the way down to the hull,

itself a critical clue.

Only once the sediment is stripped away

will they get a sense of what kind of ship this was

and what it was carrying.

But before they remove a single handful of sediment,

the archaeologists need to create

a virtual copy of the undisturbed wreck.

Each day, a pair of photographers

films and photographs the site.

High-definition video offers

a detailed visual record of the archaeological work.

While a second camera records thousands of stills.

So basically what I'm doing is,

I, I physically have a camera, an underwater camera,

and I'm just swimming back and forth

in a rather systematic way, back and forth on the site.

The roughly 4,000 images are then run through

a program that stitches them together,

producing a 3D model in a process called photogrammetry.

And then the last step is,

we basically take and we lay the photographs on top

to give it a photorealistic view.

Each day, fresh images of the site will be captured,

allowing archaeologists to

digitally retrace their steps

even after excavation is complete.

So we'll see where things came from in the 3D space.

And I think that's the really, really interesting thing

about this technique,

is that we can see this every day.

Yeah, mm-hmm. Which is fantastic.