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Could an invisible underwater force have changed the course of world history?

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How could this fleet have enormous warships remain stationary?

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This is a huge puzzle.

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How does a modern-day pirate ship evade capture for 10 years?

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Just as it seems like it's going to get caught, it's gone.

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Can a treasure trove of gold coins found in the waters off the Holy Land

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shed new light on the mysterious disappearance of an ancient city?

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To say that these coins are virtually priceless is no exaggeration.

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And there's hundreds of them littering the sea floor.

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The underwater realm is another dimension.

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It's a physically hostile place where dreams of promise can sink into darkness.

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I'm Jeremy Wade and I'm searching the world to bring you the most iconic

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and baffling underwater mysteries known to science.

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The vast majority of our ocean is unobserved, unmapped and unexplored.

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It's a dangerous frontier that swallows evidence.

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Do you have nowhere to run?

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Where unknown is normal and understanding is rare.

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The Battle of Actium, the decisive naval conflict in the last war of the Roman Republic.

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The defeat of history's most famous couple, Anthony and Cleopatra, shaped the world.

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But no one knows exactly what caused their unexpected downfall.

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Now scientists might be one step closer to solving this 2,000-year-old mystery.

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And the answer might be hiding just beneath the surface.

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September 2nd, 31 BC.

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An epic naval battle is about to take place off the coast of Greece.

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The Battle of Actium is one of the most famous naval engagements in ancient history.

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On one side, Mark Anthony and Cleopatra, Queen of Egypt,

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with an impressive fleet of 500 ships.

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They're pitted against the leader of the Roman Republic, Octavian Augustus.

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A 13-year rivalry will end here, in a battle that will shake the world.

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The stakes of this battle are high. Whoever wins, rules the Roman world, and the Roman world is the world.

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Anthony and Cleopatra's ships advance towards the enemy.

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Then something bizarre starts to happen in the waters of Actium.

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The fleet behaves very sluggishly. The boats are moving very slowly in the water.

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So the question is, why were these ships not able to maneuver like they should have been able to maneuver?

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What causes the Egyptian ships to almost stop dead in their tracks?

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It's one of the most baffling military mysteries.

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Octavian ships swoop in and destroy the fleet.

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It's a shocking defeat.

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When you look at the numbers in the battle, you say, my God, why didn't Mark Anthony win?

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He has more boats. He has bigger boats. He has the backing of Cleopatra.

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In just one extraordinary day in history, the battle of Actium is over.

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Anthony and Cleopatra's cataclysmic defeat brings an end to the Roman Republic and ushers in a new chapter in world history.

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This marks the beginning of the Roman Empire.

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So what causes Anthony and Cleopatra's ships to slow down?

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The crucial factor that gives rise to history's greatest empire.

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That question has been puzzling historians and mariners for centuries.

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In 2020, a major investigation into a strange ship-stopping phenomenon may finally provide some answers.

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Researchers begin to piece together clues hidden in ancient texts.

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Many ancient writers have discussed what happened at the Battle of Actium.

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And one of them, Pliny the Elder, says that the ships were held back by the remora.

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Remoras are flat-headed fish that sucker onto other boats and other larger fish in the sea floor.

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They use high-powered suction discs to attach to anything that's moving.

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They are the hitchhikers of the ocean.

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Is it really plausible that these moderate-sized fish could have slowed down the Egyptian fleet?

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Scientists today believe the remoras' reputation for incapacitating ships is an ancient mariners myth.

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When remoras hitch a ride on a vessel, they do create drag, but not enough to bring a ship to a halt.

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It seems highly unlikely that remoras had anything to do with the outcome of the Battle of Actium.

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If remoras aren't to blame for stopping the Egyptian fleet from advancing, something else must have been at play.

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Recent archaeological work near the naval battleground is unraveling another clue to Antony and Cleopatra's mysterious defeat.

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Following his triumph at Actium, Octavian builds a great victory monument.

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Octavian is a warlord, effectively, so monumentalizing his victory is very important to him.

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In niches in front of the monument, he displays 35 great bronze rams,

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taken as war trophies from some of Antony and Cleopatra's most important warships.

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Archaeologists discover something surprising.

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These stone niches are still there today, and by 3D scanning these niches, it's possible to calculate the size of the ships.

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Historical texts have always described Cleopatra's Egyptian warships as large galleys,

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but new technology is revealing that the size of the ships was truly exceptional.

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The ships were huge even by their day.

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They were as long as a Boeing 767 and twice as wide, and they would have been rowed by 600 men.

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Can the extreme and unconventional dimensions of the warships explain their mysterious slow behavior?

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What we have is these big armored ships, but on the opposing side, you've got a smaller, lighter kind of galley, much quicker.

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Smaller, more nimble ships may have given Octavian the upper hand.

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Having a smaller ship, you might think, is a disadvantage. How it takes less energy to get them up to speed?

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The bigger, heavier ships can't ram them because they can maneuver and then get out of the way quickly.

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But is there more to this mystery than just flawed ship design?

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A groundbreaking scientific discovery is finally unraveling what really happened that day,

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and the answer lies beneath the surface.

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How Anthony and Cleopatra lost the Battle of Actium has puzzled historians and scientists for centuries.

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But a new study of a powerful underwater phenomenon could finally solve this ancient naval mystery.

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In 2020, scientists are researching a strange nautical anomaly called dead water.

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Could this have held back Anthony and Cleopatra's ships and caused their devastating defeat?

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Dead water can slow down ships and in some instances can even stop them.

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The first person to really observe it was a famous Arctic explorer called Fridt Hof Nansen.

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And what he saw was that when he was in the fjords in Norway, however much he tried to push his ship through the water, it just didn't go anywhere.

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When Nansen encounters dead water in 1893, he has no idea what's causing his ship to slow down.

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But we now know much more about this phenomenon. It occurs where there are different levels of temperature or salinity, such as in fjords.

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In the fjords you have cold, fresh, glacial water that is sitting on top of ocean water that's more dense.

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Anthony and Cleopatra's fleet is positioned in what's known today as the Ambration Gulf.

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So do the waters here have the right features for the dead water effect?

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The Ambration Gulf has fresh water flowing in from two rivers, creating two different layers of water similar to the waters where Nansen was sailing,

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and therefore a possible location for dead water to occur.

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But could this phenomenon really have slowed down the Egyptian fleet?

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French researchers set out to solve this puzzle.

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So the way we tackled the problem of the defeat of Marc Antony and Cleopatra was first we performed some experiments in towing tanks.

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We put two layers of different densities and we just towed a plamobile boat.

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When a ship travels through water with two different densities, it creates an internal wave where the two layers meet.

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And the water tank reveals that how a ship is affected by an internal wave depends on its speed.

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If you can push yourself fast enough, you can actually get yourself out of the regime in which it happens.

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But if you can't, then you're basically stuck in it and nothing you can do is going to push your ship along any faster.

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On that day in Actium, Antony and Cleopatra's huge cumbersome ships would have struggled to escape the internal waves that they created.

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With a scale model of an Egyptian ship, Germain Rousseau and his team noticed something else extraordinary

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that could help to decode Pliny the Elder's ancient record of the battle.

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We did observe the fact that the wave pattern is modified in shallow water.

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The scale model ship creates a very familiar pattern.

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What is very peculiar is the fact that the pattern of the wave is very similar to the suction disk of a remora.

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In an extraordinary twist, Germain and his team now believe that Pliny the Elder could have been right all along.

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He was referring to the remora patterned wake and not the fish itself.

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It's likely then that the combination of huge warships and dead water created a perfect and devastating storm for Antony and Cleopatra.

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So, after 2000 years, this ancient mystery might finally be solved.

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In the South Pacific, a marine biologist sees her life flash before her eyes as she's thrown around violently underwater by a humpback whale.

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The mystery of this encounter deepens when another danger is spotted lurking nearby.

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Could there be more to this extraordinary event than meets the eye?

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September 14th, 2017.

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In the spectacular waters of Rarotonga in the Cook Islands, an extraordinary confrontation is about to take place.

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Marine biologist Nan Hauser is snorkeling in crystal clear water when she spots a 25 ton humpback whale.

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Thrilled by this once in a lifetime opportunity, she starts filming, but her initial excitement turns to fear.

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The enormous creature pushes her with its head and mouth.

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Then it pulls her under its pectoral fin and throws her out of the water.

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This woman must have been absolutely terrified to be scooped up by a multi-ton wild animal in the ocean.

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The seemingly aggressive ordeal lasts 10 minutes.

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At first, she thinks that the humpback whale is trying to attack her.

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But as the marine biologist recovers, she notices something more dangerous in the water.

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When she gets close to the boat and all her colleagues are telling her,

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It kind of changes the context in what that battering or that movement meant.

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Has the whale just saved Nan Hauser from a shark attack?

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If so, could this be the first instance ever recorded of a humpback whale protecting a human?

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This remarkable footage shows the heart-stopping moment when a marine biologist comes face to face with a humpback whale.

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I guess the most outrageous day I've ever had, and it was quite frightening.

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I mean, he's huge and your organs will rupture, your bones will break,

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but I see something and I looked and I went,

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Oh, that's the most huge, incredible tiger shark I've ever seen.

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And just at that moment, the whale was protecting me from the shark.

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You've been studying humpback whales for three decades.

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Have you ever heard stories of humpbacks protecting humans like this?

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I work with a lot of people that study humpback whales underwater,

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and this has never happened before or nor has it been reported to us.

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This humpback's behavior is baffling scientists.

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Is this whale really trying to protect Nan Hauser?

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Can other marine mammal encounters help explain this rare event?

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Dolphins have been known to surround swimmers or surfers who have gone astray and protect them from sharks.

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And it seems it's not only dolphins who have donned their heroic capes.

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This incredible photo shows another whale species coming to the aid of freediver Yang Yun.

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Her legs become paralyzed and she cannot reach the surface.

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Just then, a beluga whale swims up and uses her mouth to gently guide the freediver to the surface, in essence, saving her life.

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But an incident in Australia in 2020 gives a very different perspective

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into the behavior of the humpback that Nan Hauser encountered.

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Two women appear to have been attacked by a humpback.

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Both snorkelers were injured by a whale's tail.

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Fracturing a rib and causing internal blading.

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The humpback whale is much, much larger than these small human beings in the water, and you could potentially get injured.

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One snorkeler is left in a serious condition after being hit by a humpback's fin.

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The aggression is shocking, but this case does offer a critical clue to help understand such threatening behavior.

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In terms of trying to explain why these women might have been injured by this whale, the whale was with a calf.

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In that case, it looks very much like the mother humpback whale was protecting her young from the snorkelers.

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This shows that humpbacks are at least capable of protecting their own.

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So is Nan Hauser, like the snorkelers in Australia, a victim of a vicious attack?

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Was this the activity of a mother whale trying to protect its calf?

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There was another whale that was tail-slapping and swishing the shark.

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And was this second whale a calf?

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This was not the case. There was not a calf anywhere around. There were two grown adults.

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Turns out that these particular whales were not female. That kind of rules out that idea.

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So what other information do we have that will help us better understand what happened?

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Humpbacks are highly protective of their offspring.

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But is it possible their caring capabilities reach beyond their calves?

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Over five decades, scientists in the US have recorded more than 100 cases of humpbacks disrupting attacks carried out by their number one enemy, Orcas.

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Orcas are known as killer whales, and there's a reason for that.

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They are the top of their food chain, which includes humpback calves.

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It's natural for humpbacks to go into protection mode when an orca gets close to their young.

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But scientists recording orca hunting behavior make a bombshell discovery.

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This extraordinary photograph shows humpbacks coming to the rescue of a sea lion about to be attacked by orcas.

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It defies popular and scientific belief.

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I'm kind of surprised about it because you would think naturally the well must be protecting its own interests.

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But in this case, the wells may be protecting individuals outside of their own species.

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To witness one animal saving another from a different species is incredibly rare.

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And this could be the crucial evidence that supports Nanhauser's claim that she was saved by a humpback.

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It shows that humpback whales could be compassionate altruistic creatures.

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Altruism is when somebody does something selfless for somebody else, not expecting anything in return.

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So now we see humpback whales putting themselves at risk to protect creatures that are more vulnerable, just as a human might do.

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Nanhauser's unprecedented humpback incident has left scientists stumped.

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But she will never forget that remarkable day in Rarotonga.

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What was so amazing about the encounter is that if someone had told me this story, I never would have believed it.

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I'm serious, I had to sort of doubt myself.

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But this was something that you could never expect, ever, ever expect.

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So today I still think about it and I just can't get tears in my eyes.

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But I'm not sure what it is.

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Billions of dollars worth of treasure from biblical times to only yesterday is buried deep in the ocean.

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But the vastness of the sea floor means the chances of finding any are slim to none.

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So a group of divers in Israel can't believe their luck when they stumble across gold that the sea has been hiding for centuries.

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Not only is it ancient and priceless, it's also one of the biggest treasure troves ever discovered in the Mediterranean Sea.

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How did it survive for so long?

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2015

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Diver Zavika Fire and his friends are swimming among the sunken remains of an ancient harbour off the coast of Caesarea in Israel

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when they see something glinting on the seabed.

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At first they think it's some sort of fake coin.

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You can imagine the first thought is that it can't be real, it must be some sort of toy.

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But they couldn't be more wrong.

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As the divers sweep the sand away and pick up the tiny pieces of glinting metal,

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they are astonished to discover that this is no fake coin.

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This is real gold.

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What they discovered was absolutely incredible.

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The divers don't just find a single coin, there are more of them.

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They have a treasure trove in the palm of their hands.

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They have literally struck gold and they immediately alert the Israel Antiquities Authority.

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The divers do absolutely the right thing.

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It doesn't belong to them, they can't keep it.

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Armed with metal detectors, the divers lead the archaeologists to the site a thousand feet from the shore.

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What they discover next is mind-blowing.

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Around 2,650 gold coins were discovered here.

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There was no silver, there was no bronze, it's more than 16 pounds of gold.

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Making it the largest sum of gold coins ever discovered in Israeli coastal waters

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and perhaps the greatest treasure ever discovered in the Mediterranean.

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The mystery is how did such a large amount of gold coins end up in one spot on the sea floor?

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Where are they from? What their purpose was? How much they're worth?

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Archaeologists pull out all the stops in their attempt to solve the mystery of this massive treasure

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and new clues are about to bring to light a shocking revelation about Caesaria's past.

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Forensic investigators face a mammoth task identifying over 2,600 gold coins found off the coast of Israel.

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Fortunately, the ocean has immaculately preserved them and they're as pristine as the day they landed on the sea floor.

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But can details imprinted on the coins give up the treasure's secrets?

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Clues to a coin's origin can often be found in images but there are no illustrations on this currency.

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As these are Arabic coins they have just Arabic writing.

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So the representation of human beings and rulers, you just don't have those because it's part of that religion.

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They do however feature names of Islamic rulers and words from the Quran.

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Fortunately, we can study the Arabic writing and that can give us an indication of the date of the coins.

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The text reveals the coins are gold dinars and Islamic currency used in medieval times.

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And the dates on the coins span a very specific period of 220 years.

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Scientists were able to pinpoint these coins from the 9th to 11th century AD.

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Can events in Caesarea in this period provide a clue to the origin of these coins?

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One theory as to why these coins may be there is that in 1033 there was an earthquake and a subsequent tsunami.

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The gold coins could have been washed out to sea by a massive wave.

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A great tsunami with such strength that it pulls the massive stone blocks into the sea floor.

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If you dive on Caesarea today you can still see the remains strewn out all over the sea floor.

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And that tells us that actually things could be moved around.

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So potentially this is what has happened to the gold coins.

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But analysis of all the coins casts doubt on this theory.

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Studying the dates imprinted on the coins shows that at least 12 of them were dated a year after the tsunami hit the coast.

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This disproves the tsunami theory.

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So the coins were not swept into the sea by a tsunami.

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However the dates give the investigation team another vital clue.

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The coins all date to a period when the area was ruled by the Fatimid dynasty,

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whose empire dominated North Africa and the Middle East.

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This was an extremely wealthy and opulent dynasty,

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hinting that these coins could be incredibly valuable.

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Following this new lead investigators set out to examine the purity of the gold.

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One technique of analyzing metal artifacts we call X-ray fluorescence.

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The machine itself basically looks like a gun and it shoots back spectra that tell you the elemental composition of the metal artifact.

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X-ray fluorescence analysis confirms that these gold coins are 24 karat.

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The purest gold possible.

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These coins are basically priceless.

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We're not talking about day to day money that someone would have had in their pocket.

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As the investigators piece together the evidence, another unexpected mystery emerges,

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surrounding the historical port city where the coins are found.

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Cisarria was a very important port since its fact.

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In the first century BC by King Herod the Great.

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But in the seventh century Roman Cisarria falls to Muslim invaders.

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Its importance declines and it eventually disappears from the history books.

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It's believed that Cisarria fades from glory and becomes a fishing village until the 19th century.

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But the treasure is so incredibly valuable, the history of the city is so great.

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The 2668 pure gold coins suggest that far from being a remote rural backwater,

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Cisarria continues to be a major busy port under the new Islamic rule.

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And now investigators believe the horde was probably lost in an accident on one of the most important sites in the world.

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The history of the city is still a very long history.

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And now investigators believe the horde was probably lost in an accident on one of the many ships sailing in or out of the port.

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The Arabic text on the coins reveals another exciting clue.

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The coins showed that they weren't minted locally in Cisarria.

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So chances are very likely that these coins were being imported for some purpose.

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The question is, why were these coins being brought there?

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It's likely the coins were transported into Cisarria from the Fatimid Empire's capital in Cairo, Egypt.

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As for the reason, the coins could have played a part in one of the bloodiest conflicts of medieval times.

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A devastating religious war that shakes Cisarria to its foundations could tell us how a horde of priceless gold coins ended up on the Mediterranean sea floor.

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The first crusade was launched by Pope Irwin II as a military campaign to recapture the Holy Land for Christendom from Muslim forces.

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It was an incredibly bloody and violent conflict.

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A strong military garrison was based in Cisarria to protect it and the area around it.

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Another theory is that this treasure of coins was meant to pay their salaries.

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But does the timing of this violent uprising fit the dates written on the treasure?

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The city of Cisarria was destroyed in 1101 by the crusaders.

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And this dates quite interestingly towards the end of the time when that gold collection was put together.

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With matching dates, experts can now link the coins to this brutal massacre that kills most of Cisarria's citizens.

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You can imagine that as the Christians swept through the country, the people in the city would have been terrified.

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Amidst utter panic and chaos, could someone have thrown the horde into the sea to protect it from the Christian crusaders?

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The gold coins could be a silent witness to one of Cisarria's most dramatic and grisly events.

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We will never know for sure.

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The mystery of where this priceless horde came from and how it ended up on the seabed may never be solved.

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But its discovery is a dramatic reminder to archaeologists of the enduring promise of the sea as a hiding place for clues to our past.

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Modern day pirates steal millions of tons of fish a year in a sophisticated and lucrative enterprise worth an estimated $23 billion.

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One illegal fishing vessel with ties to organised crime is believed to have been secretly plundering our oceans for ten years, making it one of the most wanted pirate ships in the world.

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It's a relentless game of cat and mouse between ocean authorities around the globe and this elusive outlaw of the high seas.

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2018 off the coast of Madagascar. A dramatic high speed chase is taking place. A custom built high tech pirate hunter named the Ocean Warrior is chasing a notorious illegal fishing boat, the STS-50.

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This chase has been going on for days. It's like something you see in a movie.

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But after a near thousand mile chase across the Indian Ocean, the Ocean Warrior is running low on fuel. Captain makes an agonising decision to turn back and lets the modern day pirate ship go.

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This is not the first time this dangerous threatening fugitive has escaped the clutches of the law.

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The STS-50 is one of the world's most wanted ships.

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The STS-50 has slipped through authorities fingers several times.

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Twelve nations and interpol are trying to catch this vessel.

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How has this elusive ship managed to operate secretly for a decade and repeatedly escape capture?

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Two years earlier, 2016.

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At this point the ship that later became the STS-50 is sailing under a different name, the André Dolgoth.

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The vessel docks in a port in Africa.

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The André Dolgoth as its hull filled with fish, it attempts to offload in Namibia.

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It's carrying 125 tons of Antarctic tooth fish for $3.6 million.

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The tooth fish is the fish of choice for many pirates.

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They're big here in North America. You go into any grocery store and you can buy Chilean sea bass, which is tooth fish.

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And it's often referred to as white gold because it's so valuable.

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But how do the André Dolgoth and other pirate vessels manage to loot such a staggering volume of tooth fish?

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They use a variety of modern technologies to locate fish, such as sonar, and they have industrial sized machinery to operate illegal fishing nets.

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The André Dolgoth is carrying 600 illegal nets, stretching out a staggering 18 miles.

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These huge nets are known as curtains of death.

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They destroy all the life on the bottom of the sea and they catch anything that's in its way.

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In Namibia, with a jaw-dropping amount of tooth fish, the André Dolgoth is attracting unwanted attention.

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And the ship is reported to international authorities.

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But it moves on and continues to pillage the oceans.

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Then, two months later, it's caught offloading tooth fish in China.

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Chinese authorities investigate the vessel's documents.

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They discover that the André Dolgoth's registration is forged.

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But before anyone can take further action, the ship is gone.

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Evading capture, once again.

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Several countries are now trying to hunt down the André Dolgoth, desperate to crack its mysterious ways of operating.

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New methods are constantly being developed to try to tackle the issue of illegal fishing.

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Satellite technology grows every day.

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Commercial vessels over 65 feet long are legally required to carry AIS tracking transponders, which beam location data to satellites.

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Basically, that sends out a signal, gives your vessel's name so you can be tracked.

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Even with all the technology, it's still incredibly hard to find single ships in the middle of the ocean.

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Tracking the André Dolgoth becomes even more difficult when, in 2018, it changes its name to STS-50.

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One of its first stops as STS-50 is Mozambique.

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A vigilant port inspector immediately recognizes it as one of the world's most wanted ships.

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Is the net finally closing in on this notorious pirate vessel?

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Illegal pirate ship STS-50 has been operating secretly for years, but will a massive international effort bring its reign of terror to an end?

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The STS-50 is detained by authorities in Mozambique. Will its secrets at last be revealed?

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But the calls stop coming.

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The ship turns off its transponder and leaves Mozambique without a trace.

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And can you believe it? This vessel has managed to escape again.

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It's a shocking move.

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Navigating without GPS, it becomes what's known as a dark vessel, a common pirate ship MO.

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Authorities now need to up their game if they're going to catch the STS-50.

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After it escapes from Mozambique, a passing satellite spots this elusive outlaw.

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Interpol summons specialist patrol vessels to finally take it down.

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One is the ocean warrior. It manages to capture drone footage.

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The ocean warrior circulates the footage to nearby authorities, and the STS-50 is back on their radar.

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Its days are numbered.

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Indonesian authorities finally catch up with it and capture the vessel.

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The ship is seized along with 20 of its Russian and Indonesian crew, and its secrets are about to be exposed.

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A specialized forensics team pours over a wealth of intelligence found on the ship, and the evidence they unravel is dark and disturbing.

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They found links to organized crime in Europe. They found corrupt officials.

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We're not talking about local fishermen here. We're talking about a very powerful mafia-like criminal network.

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The vast majority of the crew were undocumented Indonesian fishermen who had been forced to work without pay for years.

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During a decade of piracy, the STS-50 looted an estimated $50 million worth of fish.

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How has it managed to get away with such heinous crimes for so long?

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The STS-50 is a master of disguise.

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Investigators discover this pirate ship has changed its name a total of six times, and flown the flag of eight nations.

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Illegal fishing vessels all over the world operate in complete secrecy, generating billions of dollars.

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For the authorities, it's nearly impossible to keep track of them.

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But an iconic seabird could help to bring an end to this dark industry.

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The albatross, these oceanic birds spend over 90% of their lives at sea.

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Albatrosses tend to gather around fishing vessels, and in 2019, a team of scientists sets out to research their flocking patterns.

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They tag 170 birds with a specially designed GPS that logs their coordinates.

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Officials then cross-check this with a boat's radar position.

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But the data reveals something unexpected.

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28% of the vessels the albatrosses flock around have their AIS switched off, and are likely engaged in illegal activity.

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The albatross researchers get an idea.

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Scientists have identified albatross as potentially being useful in tracking down illegal fishing.

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These giant seabirds implanted with radar tracking technology.

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When they dive into the shallow seas to get the fish that are being hauled behind these illegal pirate ships, the radars can show us where they are and when it happened.

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This new technology allows us to use albatrosses as a flying spy.

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In our attempts to stop illegal fishermen.

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For years, these majestic seabirds have been the victims of pirate fishing nets.

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But now, it's payback time.

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As they take us one step closer to bringing this secretive and destructive industry to an end.