♪♪ -218 B.C.

-- a young general leads a vast army across Europe in a surprise attack on the Roman Republic.

In his path lies an almost impossible challenge -- the foreboding Alps.

-When they arrived at the mountains and they began to climb, the full enormity of the task ahead sunk into the soldiers.

The ancient writers talk about the way that the soldiers considered these mountains to be almost supernatural.

♪♪ -It is only their belief in their daring commander that keeps them going.

That man is the legend of Carthage -- Hannibal Barca.

And that winter, he embarked on one of the most audacious military feats in history -- the crossing of the French Alps into Italy with a force of almost 40,000 soldiers, 9,000 cavalry, and, perhaps most famous of all, 37 elephants.

-I just find it so improbable elephants passing through here.

-But no one has ever found a single piece of physical evidence marking Hannibal's exact route.

Now, an international team of scientists and historians are determined to uncover where Hannibal made his epic march.

-It was an absolute revelation for us.

-I felt elated.

I'd never seen anything like that.

I mean, this isn't what happens.

-And they will recreate the journey... -Stop there.

It's really icy.

I don't think we can go there.

We have to find another way.

-...to discover how Hannibal conquered the fearsome mountains.

"Hannibal in the Alps."

♪♪ [ Wind blowing ] -The Alps.

80,000 square miles of desolate, hostile mountain terrain.

And not a trace of the extraordinary events that took place here over 2,000 years ago.

Hannibal's exact route has remained an enduring mystery.

♪♪ As the turn of the first millennium approached, the two superpowers of Carthage in North Africa and the Roman Republic were preparing for war.

Fearing a Roman invasion of Carthage, Hannibal drew up plans for a daring surprise attack.

Instead of launching an invasion by sea, he would lead an army across the French Alps, sweep through Italy, and take on the might of Rome.

Historian Eve MacDonald has spent her career following the trail of Hannibal, fascinated by the man himself.

-Getting inside the minds of people who lived 2,000 years ago is so difficult.

Even in Roman times, just after the events, there was controversy over which pass Hannibal took over the Alps.

-What is known about his path comes from ancient writers who recorded the events two millennia ago.

-Polybius is our best source by a long way.

Polybius wrote about 60 years after Hannibal crossed the Alps.

Now, he had access to eyewitnesses who were with Hannibal.

And that is why he's probably our most valuable source.

-In his account of Hannibal's crossing of the Alps, Polybius mentions numerous geographical features encountered along the route.

-The sight of Italy clearly spread out below.

The fresh fall of this year's snow.

A landslide made worse by a second and more recent landslip.

-We can use these texts almost as guides to go into the mountains and try and piece together an accurate account of the route which he took.

-Eve is joining geologist Bill Mahaney to find where Hannibal actually went across the mountains.

-I'm a mountaineer.

In the old days, I went climbing.

Later days, I did geology.

That's what I do.

-Bill is convinced the mountains must hold the key.

His team is searching for microscopic clues buried beneath the surface... -It's a good one.

-Got 50 centimeters of different environmental change.

Fantastic.

-Bill does not believe an enormous army could have moved through the mountains without leaving something behind, and he is determined to find it.

For him, discovering the truth about Hannibal's mountain crossing is a lifelong obsession.

-He was a mountain man.

He tackled a mountain experience that absolutely floors me.

I've been in the mountains with 100, 150 people.

It's pandemonium.

People fall in crevasses, people get lost off snowmobiles, people get killed.

It's crazy.

And he took 30,000 men, 37 elephants, and God knows how many horses across one of the imposing mountains in the world.

You have to admit this man was -- he knew what he was doing, and he was a man of some genius to be able to pull it off.

♪♪ -Hannibal came from a family of generals and statesmen and he was raised to see Rome as a mortal enemy.

Historian Nejib Ben Lazreg is from Tunisia, the same area as Carthage, where Hannibal's legacy is still very much alive.

-Hannibal was brought up in a family of military figures like his father Hamilcar Barca, who defeated the Romans in big battles in Sicily, and the mercenaries in Africa when they rebelled against Carthage.

-Inheriting his father's strategic brilliance, Hannibal gave Carthage its most glorious hour.

-He was a very skilled man.

And he had the ability to spot the good place where he could trap the enemy.

I consider that he is the greatest figure in our history.

[ Wind howling ] -No one knows Hannibal's exact path, but based on Polybius and other ancient guides, four main routes across the Alps are possible -- two northern routes over the Col du Mont Cenis or the Col de Clapier -- one running through the center and over the Col de Montgenèvre and a southern route-- the highest and most dangerous of all -- over the Col de la Traversette.

And Bill believes it's this southern pass Hannibal used to march his army into enemy territory.

It's a route so treacherous that most historians have dismissed it as impossible.

But Bill wants to prove the historians wrong.

-I mean, if that is the Hannibal layer, that's perfect.

-Polybius tells us that Hannibal rested his army for a few days at key points along the route.

The team hopes the troops stayed long enough to have left their mark on the land.

-They established a resting camp for two days that gave the soldiers a breathing space in which to recover.

-Bill believes this open area below the pass could be one of those resting places.

-Just imagine the troops moving down through here would have basically covered a large part of the valley.

We probably had 27,000 to 30,000 troops, 15,000 horses, 37 elephants all milling around in this place for up to five days.

They would have devastated this entire area.

Wouldn't be a blade of grass left.

And so with that, you would expect some evidence to be found in the earth.

-Soil expert Randy Dirszowsky is extracting soil cores from deep in the ground that are like timelines from the earth.

-The material at the bottom of the core is older.

It was deposited or developed a long time ago.

But as you go up further, you're getting material that has accumulated through time.

-Soil is made of distinct layers, appearing like stripes in a soil core.

The layers are created when, over the centuries, organic matter like grass decays, building up strata.

An enormous army passing through would surely have left evidence which can be found today.

-If anything were to happen on the surface, it would essentially be recorded in that layer.

If there is a disturbance of some kind, you can likely recognize it.

♪♪ -If the team can find proof Hannibal crossed the Alps via the Col de la Traversette, by far the highest and most difficult route, it will confirm he led his army on an almost impossible journey.

But Carthage was a powerful seafaring nation well positioned in the heart of the Mediterranean.

Why didn't Hannibal simply go by sea?

-In 218 B.C., the Carthaginian navy was weakened.

And the Romans had the superior navy in matter of number of war boats.

They were able to obtain big victories on the Carthaginians.

Plus, they occupied Sicily, Corsica, Sardinia, which was an obstacle for Hannibal, who had not enough boats to carry 90,000 men to reach Italy.

-If Hannibal had been forced to engage with Rome at sea, he wouldn't have stood a chance.

And he would not have been able to use his most famous and terrifying weapon -- the war elephants.

[ Elephants grunting ] Tori Herridge, an expert on ancient elephants, wants to find out more about the animals Hannibal used.

-The thought of Hannibal bringing 37 elephants over the Alps is ridiculous.

It seems completely impossible.

But he did it.

So the question becomes, how did he do it, and why?

-Moving elephants across treacherous mountains seems extravagantly difficult.

Hannibal must have had a very good reason to bring them along.

Military historian Mike Loades has a copy of a relic from the Carthaginian Empire that suggests Hannibal's motives.

-It's an exquisite coin, and it dates to Hannibal's period.

In fact, this is Hannibal's father, Hamilcar.

And on the back, we have an elephant.

-Wow.

-And the fact they've got it on this coin tells us that elephants were deeply rooted in Carthaginian culture.

We cannot think of Hannibal without the association with elephants.

But actually, war elephants weren't new with Hannibal.

-Well, kings of India were using them for centuries before they got to Carthage.

-Well, the Carthaginians were actually quite late to the game.

-I mean, how do you think he would have used the elephants in battle?

-There's been debate.

Did they have war elephants with a howdah?

That's that sort of wooden castle construction on the back.

If you have that, then you've got archers and missile men with javelins throwing down.

But if you haven't got that, then the elephant is being used as an intimidating charging machine to smash into the ranks of the Romans.

-Single rider, and the elephant itself was the weapon.

-The coin might also tell us about the nature of Hannibal's elephants.

From ancient times and even right up until the 20th century, the Asian species was used for most military operations.

But Tori has spotted something unusual.

-What you can immediately see from looking at it is you've got an African elephant on the back.

All the features are there, the shape of that ear.

Not only is it really large, but it's nice and rounded.

And look here, too.

Look.

Can you see the back?

It's got this nice, little dip in it.

That's the saddle on the back.

Shape of the spine in an African elephant has a sort of dip in it, whereas an Asian elephant kind of goes curved like that.

-Yes, yes, yes, yes.

-Today, African elephants are only found south of the Sahara Desert.

But historical records don't mention Carthaginians traveling so far to get them.

Where could Hannibal have found native African elephants closer to home?

-The Carthaginians seem to get their elephants from the Atlas Mountains.

But what we have now is a situation in North Africa where we've got no elephants whatsoever.

You've only got to go back 6,000 years, well, actually a bit less, before you get to a situation where the Sahara wasn't quite as inhospitable as it is now.

So it could be that there is a kind of a historical population of elephants that stretched all the way up to the north coast.

And then as the Sahara dried out, from about 6,000 years ago onwards, then you ended up with a remnant population up in the north that was the Carthaginian elephants.

♪♪ -The team is in the Alps, searching for remains left by Hannibal's army.

-Almost.

-But this is not their first field trip.

Back in 2015, they focused their search in France in a large, boggy area below the Col de la Traversette known as the French mire, another location where Hannibal might have rested his troops.

-Since I was certain that we had the right route, that was a place to start looking.

-A mire is a type of wetland unusual for mountain terrain.

Its grass and water could have sustained an army.

Mires form when a lack of oxygen, usually caused by water, prevents organic material from decaying fully, preserving layers of plant growth and other matter.

If the team was going to find evidence of Hannibal's army anywhere, it would be here.

They dug down and removed sections of the ground which they hoped would tell them more about the route taken.

A layer of disturbed, churned-up soil is almost invisible to the untrained eye.

-Well, actually, I didn't see the churned-up layer till we got back to Canada.

We would expect that we would find horizontal beds.

This was the normal process.

And what stood out first was at about 40 centimeters, we had this massive, churned-up bed.

-Between the layers of regular soil was one that was strikingly different.

-How do we get something like this?

Is it an earthquake?

It's possible.

But could you produce a 15 centimeter layer?

I kind of doubt that.

I'd never seen anything like that.

I mean, this isn't what happened.

Something had to disturb it.

That was my thinking.

-Something in history, something big, moved through this mountain pass and drastically altered the ground.

The team hoped it was Hannibal's army, but further tests were needed.

-I'm a scientist -- I don't too excited unless they run out of beer.

[ Laughs ] Until I see the data, I'm pretty skeptical about a lot of stuff.

So we went after the chemistry, the mineralogy, and you might say the physical process that went on to churn that thing up.

-The first step was chemical analysis, and the results helped solve one part of the puzzle.

The layer contained extremely high levels of compounds normally found in horse manure.

Bill enlisted the help of microbiologist Chris Allen to find out more.

Chris's challenge was to hunt for remnants of living organisms in the soil that might provide proof not of a few local animals grazing in the Alps, but of an army of horses.

-First thing to understand is that in soil, there are a lot of bacteria.

Now, let's imagine, just over 2,000 years ago, Hannibal comes through here with his army, and his horses start defecating everywhere.

Now, there are bacteria and feces.

And these bacteria are not like bacteria in soil.

They live on different things.

And we can see that.

It stands out very, very clearly.

-Chris analyzed each layer in the soil cores, cataloging all the bacteria that had been present in the ground for the last 2,000 years, and he found something unusual.

He came across ancient traces of bacteria called Clostridia, its remnants preserved for centuries.

-The thing about Clostridia is that it's found in lots of different organisms, lots of different environments.

But it's found at really, really high levels in the horse gut and in horse manure.

-Clostridia is normally found in soil, and it was present in tiny amounts in all the layers Chris looked at.

But in the disturbed layer of soil, it was abundant.

-If we go to either older sediments or younger sediments below that, we see levels of Clostridia that are what we'd expect to normally find in soil, so less than 1 percent.

But at this particular point, the Clostridia go to levels that are way above 12 percent, a massive increase.

It was an absolute revelation for us.

-This unusually disrupted layer of soil revealed the presence of an enormous number of horses.

-Well, I felt elated.

When I saw that, I thought, you know, this was beyond my belief that we could capture something that great.

-And carbon dating provided even more evidence.

The soil was from the same time period Hannibal made his crossing -- roughly 2,200 years ago.

♪♪ -We have independent strands of evidence telling us one thing, that at this point in history, there were a large group of animals crossing the Alps and that that group of animals, we think, were part of the army that was led by Hannibal.

♪♪ -Bill's theory that Hannibal crossed over the Col de la Traversette is now supported by microbiological evidence.

But on its own, that's not enough proof.

Polybius also mentioned numerous physical features found along the route, giving Bill and historian Eve MacDonald almost a checklist of elements to locate.

-People argue he took several routes, but this one stands right out in my mind.

It has virtually all of the environmental milestones that Polybius mentioned.

-So when you were walking around up there, you sort of could see that this one talked to you the most about matching the sources, perhaps.

-Absolutely.

-Bill believes the route over the Col de la Traversette contains all the main features that Polybius wrote about -- the commanding view of the Po River valley, from the top of the mountain where Hannibal addressed his troops.

-He had only one source of encouragement, and that was the sight of Italy clearly spread out below.

-This is an important piece of evidence for us because there is, in fact, a clear view.

-A high, sheltered position where the snow lay on the ground year round.

-The fresh fall of this year's snow had settled on top of that from the previous year, which had remained frozen since last winter.

-Currently, this is July, and, you know, here is last winter's snow in the middle of summer.

-And a treacherously steep downhill path.

-What Hannibal's men actually found was that the descent was even more difficult.

-The track was narrow and the descent precipitous.

If anyone strayed from the path or lost his footing, he fell from the heights to certain death.

-But these features can be found along several of the proposed routes.

What Bill needs is to find something unique.

-They reached a place that was so narrow that it was impossible for the elephants or the baggage animals to move forward at all.

There had been a landslide, and this had been made worse by a second and more recent landslip.

Confronted with this, the army now became thoroughly disheartened and demoralized once more.

-Polybius writes about one of the most difficult obstacles the troops encountered -- a giant landslide that stopped the army in its tracks.

-This finally led me to test the Alps for the presence of a two-tier rock fall described by Polybius.

I figured this was a key thing.

If I found the rock fall, I probably have the route.

-His soldiers might have lost hope, but Hannibal was determined to get the men and animals across.

But how did he handle 37 elephants?

♪♪ Cabárceno Park in Spain is home to Europe's largest herd of captive African elephants.

[ Elephant trumpets ] Tori Herridge is meeting chief vet Santiago Borragan Santos, who has studied the herd for decades.

His expertise might shed light on how Hannibal's men would have controlled these giants.

Every morning, Santiago follows a specific set of steps to release the elephants from their sleeping quarters.

-Oh, which one is this?

-This is Jumbo.

-Penny is always the last elephant released.

-[ Speaking Spanish ] -Here she comes.

-This is Penny.

-When she is finally let out, the herd flocks to greet her.

-Oh, look, they're all coming.

-Uh-huh.

-Instinctively, elephants follow the matriarch.

Penny coming out last limits her authority over the herd.

She can no longer lead the others or trap them inside all day, which has been known to happen.

-When they were marching in an army, you have to break the group to have the human control.

-He's going to let us know, I think.

-Yes.

-Hi, Penny.

-The only way humans can control elephants is to train each animal individually.

But a war elephant takes a long time to train.

Carthaginians might have spent decades preparing their elephants for the noise and chaos of battle.

-[ Speaking Spanish ] -They can get this elephant here to lift her foot up on command.

Well, they've got some chains there, which look really awful, but they're just every so often resting them on her legs so that she can get used to the feel and the weight and the sound and the experience of them, so that if she ever needs to be transported from here to somewhere else, they can secure her in the van that she'll move in.

They're using the gentlest of methods here -- apples and pats and instructions.

And even this has the effect of some quite considerable control.

As far as Hannibal's elephants are concerned, I'm sure the techniques weren't quite as gentle as this, but I bet they were really effective.

[ Elephants grunting ] -But no matter how well-trained the elephants were, the climb over the rock fall was difficult.

Deep in the Alps, the team has been searching for the landslide along Bill's proposed route.

This huge cascade of boulders could be what they're looking for.

-What Polybius is describing in modern terms is a slope failure of some kind.

This bulge that we see beneath us is the material that would have come from that rock fall that Polybius was describing.

-And Polybius' writings offer further proof this is likely the landslide Hannibal encountered.

-It's certain that the source that Polybius is using for this particular bit must have been an eyewitness because he's very, very specific about the distance.

"A previous breaking away of the hillside carried away about one and a half stades of the face of the mountain" -- about 300 meters.

-The 300 meters is interesting because that corresponds almost exactly to this path that we're on now.

-But there's an even more important detail that might confirm this is the landslide that halted Hannibal.

-In Polybius and his histories, he talked specifically about the presence of a two-stage rock fall, two geologic events.

One, the oldest one, bringing the slabs of rock down onto the slope, and a second one covering part of that older unit.

-To determine whether the landslide is made up of rocks that fell at two different moments in time, the team takes samples back to the base to be analyzed.

♪♪ -What happens to the rocks is, it will sit on the surface, it will undergo various interactions with the atmosphere and the biosphere.

Chemistries will change -- they will start to affect the mineralogy that's in the rock.

-When left exposed on the mountain, the rocks develop weathering rinds -- layers of distinct color on the surface.

The longer a rock is in position, the thicker the rind.

-And essentially, people usually use this to give a relative indication of time.

It's like a clock, an imperfect one, but a rough clock.

-Finding two thicknesses of rind suggests the rock fall happened in two stages.

-Those guys have quite nice rinds.

-Mm.

-Well, you've got almost 2 millimeters on this lot, Two, two and a half, maybe three.

-And now the young one.

-Yeah.

But essentially, you've got zero rind on the surface.

-So we've got an older group, and we've got a younger group.

Perfect.

That's perfect.

That fits the story exactly, yeah.

-Bill and the team examined more than a hundred rocks from the landslide and found that the rinds on samples from one half were on average ten times thicker than those from the other.

The team now has conclusive proof that these rocks broke away at two different points in time.

Polybius' final clue had at last been unlocked.

-I examined all the routes multiple times, and one of my objectives always was to look for rock fall material.

The only col that carries this prime example is the Traversette.

All the others are free of this.

They have rock fall, but an army of children could walk through most of it.

♪♪ -Standing 10,000 feet high, the Col de la Traversette is the most unexpected route because it is the most perilous.

For the army, it would have seemed like an impossible mission.

[ Wind whistling ] [ Water rushing ] Eve MacDonald has returned to the South of France to test out the route herself.

Her plan is to retrace Hannibal's footsteps at the same time of year he made his march.

Thanks to an amazing piece of astronomical evidence, she knows exactly when that was.

-Polybius tells us that it was in or around the setting of the constellation Pleiades that Hannibal got to the summit of the pass.

And if you look up at the sky tonight, you can see the moon is here and you can also see the Pleiades here, quite low in the night sky.

-The setting of the Pleiades occurs every year in early November.

To ancient eyes, it was a signal that snow would soon arrive in the mountains.

-And so Hannibal would have understood that winter was coming and he needed to get over the Alps as soon as possible.

-The decision to cross the Alps on the cusp of winter seems like madness, but Hannibal knew what he was doing.

Hannibal had followed the harvest season across Europe, and in autumn, the rivers are at their lowest ebb.

-He started his march in the late spring and early summer for weather conditions.

This was the best moment for a big army to cross the Pyrenees, southern Gaul, and the Alps.

-Even in November, the weather would have been mild until they reached the mountains.

Hannibal knew what the conditions would be because he had taken time to find new allies.

-Such a big army needed supplies on the way.

So contacts had been established with the local tribes to let him cross these regions, to guide him, too, and, at the same time, to supply him the food needed by such an army.

-But the Alps weren't the only obstacle in Hannibal's path.

His first challenge was crossing the mighty River Rhône.

Exactly where Hannibal crossed the Rhône is unknown, but clues from Polybius suggest it was somewhere between modern-day Beaucaire and Orange.

-Hannibal arrives at the bank of the Rhône River and realizes the enormity of his task.

Today, it's cold and windy, there's a mistral blowing from the north, and you get a real sense of how rough and how difficult the crossing is gonna be.

-The Rhône is the largest European river emptying into the Mediterranean.

Its waters are wild and unpredictable.

How Hannibal managed to get his elephants across the deadly currents is a feat of both engineering and biology.

-A pier of rafts lashed two-by-two was built into the water and covered with earth.

A pair of rafts was lashed to the end of the pier, and the elephants were walked onto the rafts, which were then cut free and towed across with boats.

Some elephants panicked and fell off... but were saved.

For owing to the power and length of their trunks, they kept them above the water and breathed through them, passing through the water on their feet.

-Using their trunks as snorkels intrigues elephant expert Tori Herridge.

-Swimming with a snorkel is really difficult if it's a long snorkel.

Our lungs can't cope with the differences in pressure between the air pressure at the surface and the pressure our body's experiencing.

-Human lungs can't cope with pressure changes the way elephants' can because they are surrounded by a soft gap filled with fluid -- the pleural cavity.

But this cross-section of an elephant's lung shows a clear difference.

-On those lungs, there's no sign of a cavity at all, and that is unique amongst mammals.

Elephants don't have a pleural cavity.

Instead, where that gap would be is filled up with connective tissue.

It allows them to breathe underwater much more effectively because it's much stronger, denser tissue that's resistant to that kind of pressure.

So a description that's just a tiny detail in Polybius actually fits perfectly with what we know about both elephant behavior and their internal anatomy.

♪♪ ♪♪ -After crossing the Rhône, Hannibal didn't take the well-known route along the Durance River because there was a major threat to the south in nearby Marseille.

Eve and Tori are trying to understand the decisions that led him to the Col de la Traversette.

-His intelligence tells him that the Roman general, Publius Scipio, is at the city of Marseille.

-Ah.

-And the last thing Hannibal wants to do is engage with Roman armies.

He has to, if he's going to succeed in his plan, engage with the Romans in Italy.

-Can't go south because of the Romans.

Only option, then, is to head north.

-One of the most likely options is the Drôme River Valley, which comes off the Rhône and heads up into the mountains and then rejoins the Durance river.

And there's a place on the way where the path divides, and at that place, he makes an unexpected move.

♪♪ -At this pivotal fork in Hannibal's route, Eve and Tori team up with mountain guide Damien Juhen.

Uncovering the next steps in Hannibal's journey requires some expert local knowledge.

-Here, we are exactly at the confluence between the Durance River on your left and the Guil River in front of you.

The Guil River is going through the gorge, really steep and narrow gorge, the Guil Gorge, and the Durance is going down to the Mediterranean Sea.

-And that's the way that Hannibal would have come in, yeah?

-Yeah.

And at the fork, he had to make a pretty critical decision.

He had to decide whether to continue up along the Durance River, or he could veer off here up the Guil River and take the road less traveled, the road that no one would have expected him to take, and also the shorter route into Italy.

-Why did he choose the road less travelled?

-Because that's very much his personality.

He was always somebody who's into surprising the enemy.

♪♪ -But this decision proved almost fatal.

Hannibal and his army soon found themselves at the bottom of a gorge with wall after wall of sheer rock towering over them.

-So, when Hannibal came down into the valley, you arrive, and it's like a wall.

Okay?

And it's really impressive.

I mean, even for me, the first time I came here, it was -- I said, "Where is -- Where is the road?"

So I think that for him, it was really hard.

-How long would it take to walk the gorge?

-Nearly a day.

It takes a long time for these 20 K's of gorge.

-So for an army laden down with animals, in difficult conditions, it would have been more than one-day walk?

-Oh, for sure, yeah.

For sure, yes.

More than three days maybe.

-Slowly marching through the gorge put the troops in a vulnerable position.

And local tribes were only too eager to take advantage of it.

-He runs into some locals who pretend to be "friendly," so-called friendly guides, but he's suspicious.

And two days into this march, Polybius tells us that these new friends attacked the Carthaginians as they were traversing a certain difficult and precipitous gorge.

-And this gorge here fits that description quite well.

So just try to imagine, all up above here, Celtic tribesmen hurling boulders, rocks, projectiles, anything they could find, down on the soldiers and the animals, and picking them off one by one.

-The horses went mad with terror at the wild shouts, which echoed and re-echoed ever more loudly from the forests and mountainsides, while chance blows and wounds so panicked them that they wrought havoc among the men.

[ Horse neighs ] -You can imagine the noise, the chaos, the animals turning around, people dodging, trying to take cover.

People are falling into the river.

And there was no way for them to defend themselves.

-The tribesmen took whatever plunder they could.

♪♪ By the following day, they were gone.

♪♪ Hannibal sustained huge losses, his men and animals scattered across the gorge.

The horses proved to be a liability in the mountains, and their panic only made the attack worse.

But they were a crucial military weapon that Hannibal could not do without.

Half of them belonged to his elite mounted force.

-The Numidians were light cavalry.

They came from North Africa.

They were lightly clad and famously rode without saddles and even without bridles.

They used just a simple neck rope.

that's all they had.

♪♪ -The Numidians were armed with fistfuls of javelins, riding at the enemy and repeatedly throwing their spears.

They were hit-and-run troops.

-Riding without a saddle?

Stirrups hadn't been invented.

Riding without a bit and a bridle is challenging.

It's only possible on a fantastically trained horse like this.

-The fact that the Numidians actually went into battle like that is mind-blowing.

I can't imagine.

But they must have had such control, such a relationship with their horses.

This horse should follow me.

Hup!

So without any tack, without bridles and stirrups and all of that sort of thing, he's silent, it's stealthy.

It's the perfect horse for scouting.

Imagine them in the Alps.

If you're going over treacherous terrain, you can get off, and the horse will follow you.

-On Hannibal's journey, the Numidian cavalry were frequently sent ahead to gather intelligence.

And they possessed a special skill that gave them the element of surprise.

-They would lay their horses down.

[ Clicks tongue ] It's perfectly comfortable for the horse.

There he goes.

There!

Look at that.

Now, just think how useful that is if you're a scout.

You can get really low behind the tall grasses and scout the enemy's camp, count their numbers.

Then they could simply get on their horses.

[ Grunts ] They were the eyes and ears of Hannibal's invasion force.

[ Clicks tongue ] Hah!

-But the horses weren't the only animals that had to endure the long march to the top of the mountain.

So, too, did Hannibal's famous elephants.

At the Royal Veterinary College in London, Professor John Hutchinson has a rather grisly piece of evidence that reveals why elephants are so well-suited for long and hazardous journeys.

-Back foot.

-It is the left hind foot of an adult Asian elephant.

-Donated to science by a zoo, it shows that elephants, surprisingly, can be very good mountain climbers.

-So you can see that he's up on tip-toe -- that's really remarkable about elephants.

So you can see the heel up here.

That would be the ankle joint.

And then the middle toe, the third toe, going down here.

So the elephant's up on tip-toe.

-I love that, the fact that you look at them from the outside and they look so sort of straight and flat-footed.

-Mm.

-But then you look inside them, and it's a completely different story.

-Yeah, it sure is.

And then look at what we have here on the back half of the foot.

There's this massive, yellowish, white tissue.

It's all fat pad.

Just like our heel pad on our foot, but massive.

-When you imagine an elephant moving through the mountainous areas, they might have been better off than something with a hoof.

-Yeah.

Elephants have a foot that is able to change its shape to suit the environment.

-But it's not just the structure of the foot that makes elephants well-adapted for Hannibal's mission.

They are also very efficient when in motion.

-As we see in this video, the limbs are really straight when they're supporting the body and walking, so they're like pillars.

The elephant only flexes its joints mainly when the feet are off the ground, so the muscles don't have to exert as much force to support an elephant's weight.

-Perfect for long-distance travel.

-It is.

They have a really flexible way of moving.

And very steep slopes, they'll get down on their knees, basically, and crawl along to get up high slopes.

They have that kind of stability and economy that is uniquely elephant.

[ Bird cries ] ♪♪ -And there's proof that elephants can cross the Alps... -[ Laughs ] Crazy.

-...thanks to an extraordinary experiment conducted almost 60 years ago.

-Wow.

Actually, Jumbo looks larger than I was remembering.

-In the summer of 1959, British engineer John Hoyte led a team of scientists and explorers on one of the most ambitious experimental archaeology events ever attempted -- taking an elephant over the Alps in Hannibal's footsteps.

Sir Richard Jolly was second in command.

-The scientific part of our expedition was a very careful checking of Jumbo's speed along the level and when ascending towards the summit and as high as 2,083 meters.

We were seeing whether the difference in altitude and the climbing challenge slowed Jumbo down in any way.

And the short answer was no, it didn't.

I think the elephants, they're very sensitive creatures, and if well-trained, very confident and in control of themselves.

[ Laughs ] Yeah, and there's Jumbo having some fun.

Good, old Jumbo.

Hmm.

-So elephants, despite living in warmer climates, can endure the cold and alpine terrain in short bursts.

[ Elephant trumpets ] With winter approaching and the troops delayed, Hannibal needed to speed up the march, so he loaded his pack animals with rations.

Even the humble donkey was essential.

Tori and Eve are attempting the final leg of Hannibal's climb into Italy, going up to the Col de la Traversette and testing out how the army would have coped.

-If you're on a mission to be as quick, moving as fast and as light as possible, then you're gonna always have to trade-off between what you carry and what you collect.

And so the more you carry, the less time you've got to spend foraging.

-And once he starts to go up to the mountains, he's gonna have to be carrying an awful lot of food because there really isn't much capacity up here to forage.

-The donkeys would have carried about 220 pounds worth of hay, enough food to feed one horse for 20 days.

However, Hannibal had 9,000 horses and 37 voracious elephants.

Using historical records, scholars have estimated how much food the troops and pack animals needed.

But for the elephants, it's not clear.

-Mm-hmm.

Mm-hmm.

-And they also eat the grass outside, of course.

-Si.

-Elephants are big, hungry beasts.

An adult elephant can consume up to 300 pounds of food in a single day and a lot more if constantly on the march.

[ Bird cries ] As they pushed on toward the Col de la Traversette, Hannibal's exhausted army would have been spread across 20 miles of the mountain range.

The ancient texts state that in these barren mountains, the food supplies ran out.

♪♪ -The animals were nearly dead from starvation, since the high passes were almost totally devoid of vegetation, and whatever fodder there might have been was buried under snow.

-Something had clearly gone wrong in Hannibal's planning.

-We're gonna stop there just a second.

-The team encounters a problem that Hannibal himself must have faced in early November.

-Now we are up to 2,500 meters elevation, and the path become really, really hard, difficult because it's steep and really icy and with the donkey, we can't, go through.

For us, it can be okay, but with donkeys, it's impossible, for sure.

-And then you get something like this, and there's no way you'd get a beast up there.

They'd have to go ahead and hack the ice off.

And even then, you can imagine the situation where something lost its footing and just slid.

-We have so many tales of it.

And it's amazing that two or three times we get this sense of these pack animals knocking people and themselves and other horses and everything off the pass.

-Many pack animals must have died on these steep, icy slopes.

Losing any of them would have been a real concern for an army wholly dependent on the food they carried.

-As you lose your pack animals, like, it's not just the beast that's dead.

It's, you know, that's -- that's, 100 kilograms of load that you can no longer take with you.

That's 20 days of horse feed.

-And that's what Polybius says is, by the time they get over the other side to anywhere that's good grazing, the animals are starving.

-Hmm.

-So, I mean, that's it.

They've lost so much of their supplies just coming up the sort of dangerous routes like this.

♪♪ -The army marched for nine days in the Alps, camping in the freezing cold, moving night and day.

♪♪ At long last, after a desolate climb, Hannibal reached the Col de la Traversette.

From high atop the mountain, the view of Italy and the prospect of conquest stretched out before him.

-Here we are, France on one side, Italy on the other, standing on the border.

-His army must be spread out all down the valley.

It takes two days for everybody to come -- 30,000 men and maybe 10,000 pack animals, and, of course, 37 elephants.

♪♪ -Hannibal needs to make them believe that they can do what they set out to do.

And he encourages his army with stories of all the riches and the wealth to be won and of all the heroic adventures that lie ahead of them.

-The monumental Alps, with their snowy spires and craggy slopes, met their match.

Now, for the first time, scientific evidence is confirming the historic event -- that Hannibal crossed these mountains at the highest and most difficult pass of them all, the Col de la Traversette.

-Finally, we are pulling together some scientific evidence that this is the route that he took across the Alps.

And who would have expected that this could be coming down to something as simple and tiny as the bacteria hidden in the soil?

-We finally had narrowed the pass down to one place.

-A journey that became legendary has now been made real.

-Whilst it was difficult, whilst it would have been bloody, there would have been deaths of both people and of animals, at each stage, I don't think any of those problems were insurmountable.

If you're willing to push, then why not?

You could do it.

-Hannibal's invasion of Rome over the Alps sent shock waves through the ancient world.

By the end of the year, he had won two decisive battles on Roman soil.

Carthage was safe for now.

For 15 long years, he waged a campaign of annihilation throughout Italy.

But eventually, Rome stood strong once more, and the tide of victory turned.

Hannibal was finally defeated on home soil, and Carthage was left in ruins.

But 2,000 years later, his incredible journey over the Alps stands as a testament to his unflinching determination and military genius.

-This was undoubtedly the most difficult pass Hannibal could have taken.

And we sort of have to ask ourselves, why did he take the hardest route?

And what probably drove that decision lay in what made the man who he was.

Because the more difficult the journey, the more difficult his quest almost, the greater his heroic status would be.

2,200 years later, we're still absolutely fascinated by Hannibal and especially by this journey he made over the Alps.

-He created the myth, and we still believe it.

-Hannibal's journey was legendary, and now we know it wasn't a myth.

♪♪