♪♪ -Ancient Rome... heart of a powerful empire.

And home to an architectural masterpiece -- the Colosseum.

-The Colosseum is the largest amphitheater ever built in the Roman world, the most famous, the most impressive monument in the ancient city of Rome.

-Built to amaze... but also, to entertain... educate... and control.

-Argh!

[ Cheering ] -We get a sense of incredible engineering, incredible architecture, and of course, what took place here is something that still leaves us in awe.

-Now archaeologists are taking a closer look at this icon of the Roman Empire... revealing its former glory.

-The most exciting thing about this excavation is that it gave us the opportunity to touch the very origin of the Colosseum.

-And further research across the Roman world is shedding light on long-held myths about this great amphitheater and the empire itself.

-It makes it possible to prove what they ate, how they lived, how they trained.

So, it was just super exciting.

-How does the Colosseum, and the games that went on inside, reflect Rome's political, financial, and military fortunes?

-It's, in many ways, one of the most political buildings of the city of Rome, and arguably, of the Roman Empire as a whole.

♪♪ ♪♪ -The year is 80 CE.

50,000 Romans, from senators to slaves, arrive at the brand-new Colosseum.

Entrance is free -- a gift from the emperor.

The inaugural games are about to begin.

♪♪ Trained hunters, known as venatores, slaughter exotic animals from across the empire.

[ Roars ] Criminals are forced to act out ancient myths... before their execution.

And the highlight?

Gladiator fights.

Hundreds of them.

♪♪ -What you see inside the games is a microcosm of the reality of the world order.

Rome is in charge.

The Emperor is in charge.

-When those first games were held, the emperor ruled over territory that spread from North Africa to Germany, from the north of England to Syria.

Over 40 million people.

Two million square miles.

The opening of the Colosseum marked the dawn of Rome's Golden Age, a period of peace, strength, and immense prosperity.

-This is the epicenter of the entire Roman Empire under the emperors.

-Two thousand years later, only portions of the amphitheater remain.

The wooden arena floor, seating stands, and internal corridors have long since collapsed.

Now a new large-scale excavation of the Colosseum is underway... -There it is.

There.

These are the splinters from the boards of the wooden frame.

We're going to conserve it and take it to be analyzed.

-Researchers want to understand how the Colosseum was built, and what it originally looked like.

-Buongiorno.

-Lead archaeologist Federica Rinaldi... -Buongiorno.

-...oversees the team.

♪♪ -[ Speaking Italian ] -We are working on the Colosseum's southern side, an area that very little is known about.

-Only the northern facade of the Colosseum remains standing.

To the south, an earthquake in the 14th century brought down the outer corridors and walls... an area later paved over.

♪♪ The archaeologists are digging where these structures once stood, down into the Colosseum's very foundations.

-[ Speaking Italian ] -We decided to remove this cobblestone pavement and start digging layer by layer this immense area of 3,000 square meters to restore the story of the Colosseum.

It's the first systematic exploration of this vast area, that once supported two huge parallel corridors.

Technical architect Barbara Nazzaro is part of the research team.

She is studying the methods used to build the Colosseum.

-This is a very, very hard concrete made with mortar and a basaltic stone, which gives a very, very hard foundation because we know that the Colosseum was nearly 50 meters high.

It was very heavy.

And, so, it needed a very deep foundation.

The foundation is two levels that are more or less 14 meters.

-The thick foundations, thought to extend under the whole structure, are nearly 45 feet in depth, and held the weight of the massive Colosseum, an estimated 990 million pounds.

The immense weight came from its building materials -- limestone, dense volcanic rock, bricks, concrete, and thousands of iron clamps that held the stones together.

Today, much of the original material is gone, taken and reused over time.

But there's enough left of the Colosseum for archaeologists to understand how the crowds entered this great structure to enjoy the games.

-[ Speaking Italian ] -The entrances to the Colosseum took place along a radial axis, not via a circular route like today.

There were in fact 76 entrances for the public who entered in this direction.

Each had a ticket on which was engraved the number of the arcade they had to go through.

And then, going up the stairs, they would reach their seats.

♪♪ -Important officials and various organizations like guilds allocated tickets to citizens.

But who were the spectators that came to watch the games?

And once through the numbered arches, how did they know where to sit?

While much of the Colosseum's internal structure has long since collapsed... Pompeii is home to the first stone amphitheater ever built.

It's 150 years older than the Colosseum, and much better preserved.

Darius Arya has studied the remains in detail.

-We have some corridors that lead you directly to the best seats in the house, the ringside seats.

And then we have external staircases all around here, and that's going to take you to the higher located seats.

-The stadium was designed to maintain a strict segregation of social classes.

-What we see is that there's a rigid categorization of people.

You literally have a blueprint of how society works.

The most important people have the best seats, are closest to the action, and as you make your way up into the nosebleed seats, well, you're less and less important, reminding you of your place in that Roman society.

♪♪ -Classics historian Shushma Malik has spotted clues suggesting the same was true at the Colosseum.

-When we think about the seating arrangements, the different levels are made from different materials.

So, at the bottom, we've got more brick and solid stone.

But as we work our way up to the top, the materials become wooden, so less comfortable, less secure.

This represents a difference in who's sitting in the different places in the Colosseum.

-On the ground floor, huge corridors, 30 feet tall, display exquisite reliefs.

The top-floor arcades are smaller and left plain.

-At the bottom, we've got the elites.

So, we're talking about senators and equestrians, who were the richest people in society.

And then, as we go further up, in our next layer, we've got male citizens.

And then, as we go further up, you have the other category of society, which is the rest, essentially.

So, non-citizens, the enslaved, and women.

-Everyone in the crowd knew their place.

♪♪ -We're looking really at a space that restates the political and social order and that, on the one hand, gives people plenty of entertainment and plenty of fun, but also gives the people in charge -- the men in charge -- the opportunity to control very closely who's doing what and where.

-The Colosseum was more than a place for entertainment.

It was a demonstration of power to maintain control.

And from the remains uncovered by the archaeologists today, it's possible to understand what the Colosseum looked like when it hosted gladiator games.

♪♪ -[ Speaking Italian ] In front of me there's a square section that has a very smooth surface.

On top of this footprint there would have rested blocks of travertine, at least 90 centimeters tall.

They formed the base of the pillars that supported the arches.

-Travertine is a dense type of limestone that was quarried locally.

Archaeologists estimate that more than 250,000 tons were used to build the Colosseum.

The uncovered architectural footprints reveal where lost archways once stood... and enable archaeologists to create a virtual model of the Colosseum with its collapsed southern wall still intact.

108 arcades stood here, stacked on top of each other over three floors, almost 130 feet in the air.

On the ground floor, senators and senior politicians reached ringside seats through corridors reserved exclusively for their use... while the public followed a network of staircases and hallways that took them to seats determined by social status.

♪♪ And at the center of the amphitheater -- the emperor and his entourage.

♪♪ The archaeology here has revealed detailed information about what the Colosseum looked like when first built.

But there's still more to uncover.

-What they did is to create these drains inside the foundation.

The floor of these drains was made with bipedalli, which are square bricks.

-The drains would have prevented the Colosseum from flooding during heavy rains and taken away whatever refuse built up on game days.

-This was full of things like nowadays' drains, so water, rubbish, something coming from toilets, and any washing and cleaning that was done inside.

Also, bones from food, seeds of the food they ate during the day.

And probably some animals that were killed inside, too.

-But the drains reveal something else.

-Maria Rosaria, look, there's a stamp.

Can you see its shape?

-Yes, it's a half-moon.

I can read "Rufi."

-Okay.

-The Romans stamped their bricks so that each factory could be held accountable for the quality of its products.

-[ Speaking Italian ] -Thanks to the huge database of brick stamps from Imperial Rome, we can say that this stamp dates to Vespasian's time.

-It's proof that the Colosseum's foundation was built in the reign of Vespasian, the ninth emperor of Rome.

He took the throne in 69 CE.

-Vespasian comes up with the decision of building the amphitheater in Rome in the early months, really, of his reign.

The project begins in earnest in 72 CE.

-Why did he build the Colosseum and choose this location for it?

Vespasian followed the reign of an infamous ruler -- Nero.

Just yards from the Forum, the central hub of ancient Rome, Nero had built himself a huge palatial complex -- the Domus Aurea, or the Golden House.

-The very construction of that palace had led to the eviction of thousands of people from, really, a central site in the city of Rome.

So, it is a monument of despotism.

It is a monument of extravagance and imperial corruption.

-And Nero didn't stop there.

Alongside his grand estate, he built a huge statue of himself, 100 feet tall, known as the Colossus.

-So, we're talking about a megalomaniac.

We're talking about a person that wants to leave his mark on the city.

-After Nero's death, warring factions attempted to claim the Roman throne.

-In the political fallout, there's a lot of bloodshed, there's a lot of uncertainty.

And from that competition, that "Game of Thrones" experience, there's one man that remains standing.

His name was Vespasian.

-Vespasian was not of royal blood, but a military man, a general.

His first challenge -- building a relationship with his people.

[ Soldiers cheering ] So what did he do?

-[ Speaking Italian ] -Vespasian is on an important political, populist mission.

He gives back to the people what Nero had taken away and builds the greatest structure for spectacles in the Roman Empire.

-Vespasian built the Colosseum on the grounds of Nero's vast estate.

And the Colossus statue was reshaped into the Roman god Sol.

Savvy political gestures to erase Nero's legacy and establish a new dynasty -- the Flavians.

♪♪ -The building of the Flavian Amphitheater was central to the political program of Vespasian.

It was, first and foremost, a major statement of the fact that he was the new guy in charge.

-By 80 CE, after only eight years, the great amphitheater is finished.

♪♪ ♪♪ But the emperor celebrating the first ever games at the Colosseum isn't Vespasian.

-Vespasian had a very distinguished career as emperor.

He transforms the city, building the first public amphitheater on such a grand scale.

Unfortunately for him, he didn't live to see its completion.

-Vespasian achieves something very remarkable.

He dies in his own bed.

Never a mean feat for a Roman emperor.

-Vespasian dies only months before the Colosseum's grand opening.

-Titus succeeds his father.

He gets the glory of celebrating the games.

-It was, in many ways, his big day.

[ Crowd cheering ] He was, by inaugurating the amphitheater, as it was then known, announcing, advertising, stating the beginning of a new era, of a new golden era.

♪♪ -Rome's Golden Age would see the empire reach peak prosperity and military strength.

How did the entertainment within the Colosseum reflect the grandeur of the mighty Roman Empire?

-The main event in the afternoon each day, it's man against man.

It's world-famous gladiators going head-to-head.

-Gladiators are central to our story -- public entertainment in Rome.

They are central to the story of the Colosseum.

-The Colosseum was primarily built to host gladiatorial contests.

It would become the most iconic venue for these spectacles.

But there was more to these clashes than a simple fight to the death.

♪♪ In Rome, Alexander Mariotti is a specialist in gladiatorial combat.

He believes the only way to truly understand a gladiator is to become one.

-Experimental archaeology is an interesting way to get another perspective that the sources don't give us.

Once you put on the armor, once you fight with the weapons, you start to gain a physical knowledge and a physical memory.

You understand the hardships -- things as simple as the inability to breathe, your perception of what you can actually see, the weight of the helmet, the tiredness that comes through the physical combat.

So, it's a great way of sort of filling in the gaps that we have through history.

The sport is entirely different than we've been led to believe.

-Every time I go in the arena, I think about the real gladiators, what they have in the mind, you know.

A lot of people want to see you fight and see the blood.

So, you should make entertainment for the people of Rome.

♪♪ ♪♪ -More than 15 different classes of gladiators, distinguished by their weapons, armor, and fighting styles, fought inside the Colosseum.

♪♪ -Through their armor, through their weapons, they have advantages and disadvantages, strengths and weaknesses.

-One of the most popular battles was between two specific classes -- the retiarius versus the secutor.

-This is a fan favorite.

This is the retiarius.

He was the only one whose face you could see, and that made him human.

The thing about gladiator helmets is that they dehumanized the fighter.

He became more of a robot.

He didn't show expressions of pain.

Whereas the retiarius is us.

We can see him.

We can see his expressions.

-As a way of projecting authority over the Roman people, many classes of gladiators were inspired by the ancient enemies of Rome.

But by the time the Colosseum was inaugurated in 80 CE, most gladiators were professional athletes who chose to fight.

The retiarius was a newer class of gladiator.

Fighting without a helmet, he was an everyman, a simple fisherman.

-So, he has two weapons, which are pretty iconic.

He's got a trident over here and a net.

The net is a really a very dramatic piece of equipment.

You can imagine them swinging it in the middle of the arena, the people loving it.

-The retiarius had the advantage of mobility, but little protection, unlike his opponents.

-The secutor here is a tank.

He's got not only this massive helmet, which, if you look at it objectively, has a little bit of a fishlike quality -- small eye holes, a fin on the top.

And, so, we have a theme to the fight.

♪♪ This is a fight of nature.

Man versus nature.

The fish against the fisherman.

♪♪ -Man versus nature.

Rome against its enemies.

Gladiator fights were more than sporting contests.

They were a part of Rome's national identity.

-And it's the clash of these two -- who's going to win?

-- that makes it exciting for the Roman audience.

That's what it is.

It's a show.

-During Rome's Golden Age, the Colosseum would showcase around 100 gladiatorial fights per year.

Most games were organized by the emperor, but also by wealthy aristocrats intending to further their political careers.

How did Rome produce enough skilled fighters to keep the crowds entertained?

♪♪ More than 400 miles from Rome lay the border town of Carnuntum, in what is today Austria.

The remains of these amphitheaters -- almost two miles apart -- are nearly all that's visible of the settlement today.

Professor Wolfgang Neubauer has been working at the site for over 30 years.

-The Roman Carnuntum was really an important town.

It is one of the hot spots of the Roman Empire in the second and third century.

-Located on the banks of the Danube River, Carnuntum was a thriving center of commerce and home to 50,000 citizens.

And it still lies here, untouched, under farmland and pristine countryside.

-Carnuntum is very special because it has never been overbuilt.

All the remains are still preserved in the ground.

So, it's all there.

♪♪ The town is about 10 square kilometers.

It's absolutely impossible to excavate something like this.

But there is another way to do archaeology.

♪♪ -Wolfgang and his team are pioneers of noninvasive archaeology.

They combine lidar, ground-penetrating radar, and magnetometry to create detailed models of the structures below the ground.

♪♪ Wolfgang's survey reveals the sprawling infrastructure around the larger of the two amphitheaters... for the first time.

-We can actually really walk into this data and see all the different details.

-And one mysterious building stands out.

The scans show four stone walls surrounding a round wooden structure, more than 60 feet in diameter.

-The most amazing thing was that circular structure.

And when we look closer to this circular structure, it looked like a small amphitheater.

And in the center of the circular feature was one individual hole, a post hole.

We realized that this might be the foundation of a palus.

-Roman sources describe the palus as a wooden post that gladiators used to practice their sword blows -- like a timber punching bag.

One typical place to find a palus would have been a gladiator school.

-We had to verify this, so we made an excavation and we found the foundation of the palus in the center of the training arena.

And this made it clear that we really found a school of gladiators in Carnuntum.

-This gladiator school has remained preserved beneath the ground for almost 2,000 years.

It's the first of its kind to be found outside Italy.

While the first gladiators were simply prisoners of war, over time, a whole industry developed around the games' participants.

Even free men chose the life of a gladiator... ...and were turned into professional fighters in schools such as this one.

And the most prestigious school of all was discovered in the 1930s, under a city block adjacent to the Colosseum.

-Right here, in the shadow of the Colosseum, is this large, sprawling complex.

You can actually see quite clearly there's a massive, curved wall.

This structure is an amphitheater.

But what is another arena doing right next to the Colosseum?

This structure is known as the Ludus Magnus.

And that means, in Latin, the "big school."

So, this is really the epitome of gladiator schools throughout the Roman Empire.

This is number one.

-Evidence of its lost grandeur is still easy to spot.

-Let's take a look right here.

All right.

So, what you have here is a marble plug, and then right next to it's a little piece of a metal pin.

That's part of the attachment system to which you would adhere panels of marble.

Those panels of marble have been stripped away, but this tells us they were there, which means that this gladiator school was beautifully decorated.

Because the emperors own this, it means money is no object.

This is just imperial magnificence.

You can imagine the emperor coming to watch some of the performances in this practice arena.

That's the prestige of the Ludus Magnus.

The barracks were at least two, even three stories high.

So, hundreds and hundreds of gladiators.

Every day they're practicing, they're training, getting ready for the main event in the Colosseum.

♪♪ You want to think about it being like coming to Madison Square Garden.

You've made it, you've established yourself.

You're coming from all over the empire, and now you're going to the great big show.

-The remains of the gladiator school hint at how far the Romans went to provide the best entertainment.

But is there a way to learn more about the gladiators themselves?

♪♪ Vienna, Austria... home to the lab of forensic anthropologist Fabian Kanz, an expert in human remains.

-For us, as humans, everything we do leaves traces in our skeleton.

♪♪ -Fabian and his team were called in to examine the remains of more than 60 bodies, found buried in a mass grave over 600 miles from the Colosseum, in a Roman cemetery in Ephesus, Turkey.

All but one turned out to be male.

-Then we start finding injuries.

It was just overwhelming how many injuries we found.

♪♪ There are just two options.

Maybe they have been soldiers.

Or they have been gladiators.

What is really impressive on this skull is a really massive sharp force wound, and there's kind of tearing, which means this must be caused by a barbed instrument.

-The only weapon that could have torn bones in this way was the barbed tip of a trident.

And only gladiators used tridents in combat -- never soldiers.

-There was a moment where we put all these clues together.

We have this group with just males in it.

We have this very high amount of healed and unhealed trauma.

This all together fitted very well that these are the remains of gladiators.

-These are the first gladiator bones ever found, let alone studied in this kind of detail.

-It makes it possible to prove what they ate, how they lived, how they trained.

So, it was just super exciting.

-Signs of damage to one of the skulls catch Fabian's eye.

He zooms in to inspect the wound more closely.

-This is the frontal bone of the skull.

And as you can see here, there's a massive sharp force trauma.

The chance to survive this is very low.

But you can see all the borders of the injury are smooth.

This means it was professionally treated -- all the little bone splints and everything picked out, therefore, it recovered nearly perfectly.

-It's evidence that this person was treated for a severe skull fracture and survived... proof that gladiators received sophisticated medical attention.

The most renowned physician in the Roman Empire, Galen, wrote about treating wounded gladiators in his city of Pergamon, in modern-day Turkey.

He claims to have saved all the men in his care.

-We know from the books that gladiators have the best medical treatment at the time, but now we have the physical evidence to prove this.

-Ancient accounts also reveal that the training and upkeep of these warriors was financed by the managers of gladiator schools.

It was a big investment.

A lot of money could be made from top gladiators performing well at lavish games organized by rich Romans or the emperor.

But did the special treatment of gladiators go beyond emergency medicine?

Fabian cuts a bone sample... ...and freeze-dries the fragment with liquid nitrogen... ...before grinding it into powder, and mixing it into a solution.

♪♪ A flame spectrometer can reveal the presence of different elements in a liquid, to analyze its chemical composition.

Fabian tests the bone solution for any unusual elements.

The flame burns bright red... -You see, it's very intense.

-Evidence of the element strontium.

Strontium, normally found in only trace amounts, strengthens bones, improving mobility, making them more resistant to fractures, and protecting vital organs from injury.

All of which would enhance the fitness of a fighter and perhaps make the difference between life and death in combat.

But these gladiator bones contain unusually large amounts.

-It was not just a little bit more, they had double the amount than normal people at that time.

-The body obtains strontium primarily through dietary intake.

Ancient texts mention that gladiators drank a special brew, made from burned bones or plants.

-Burning bones, wood, or bark to ash increases natural strontium levels.

Drinking this mixture boosted the gladiators' intake.

Fabian believes this could explain the superhuman levels of strontium in the skeletons.

-You have to think about this ash drink like we drink nowadays after sports, these fizzy tablets.

And this was pretty much the same.

[ Gladiators grunting ] -From advanced healthcare to strontium supplements, nothing was spared in pursuit of the ultimate warrior.

♪♪ But there was more to the Colosseum than just gladiator fights.

Hunting wild animals was also hugely popular.

[ Roars ] And new archaeology and research reveal the scope of these performances.

At the Sapienza University of Rome, zooarchaeologist Claudia Minniti examines animal remains recovered from the Colosseum's sewer systems.

-The Colosseum is the only amphitheater which has given us such a vast quantity of animal remains.

It's an exceptional collection.

♪♪ -Cleaning them reveals details that can identify the animals.

♪♪ Carnivores usually have sharp teeth for cutting and tearing meat, whereas herbivores' teeth are flat.

-[ Speaking Italian ] -This skull has teeth that are characteristic of a carnivore, although it must have had a somewhat omnivorous diet because the teeth have both sharp and flat surfaces.

From the teeth, I can tell this is a bear.

-Other skulls belong to everyday animals -- horses and dogs.

But Claudia homes in on a more unusual find.

-Here we have two radius bones from different individuals.

-The radius is a bone found in the front legs of animals.

-[ Speaking Italian ] -They are the same shape as the radius of a domestic cat.

This tells me that we are dealing with the remains of large felines.

♪♪ -To identify which species, Claudia compares the size of these bones to those of big cats living today.

♪♪ -[ Speaking Italian ] -These are therefore two large individuals that fall within the range of lions.

In particular, the largest bone proves to be very large, probably belonging to a very large male, which was specifically chosen to be used in the games.

-This collection of bones also reveals lions weren't the only exotic animals used in the Colosseum.

-[ Speaking Italian ] -This measurement fits within the range of a leopard, rather than a lion.

-These animals, from far-flung corners of the empire, left the crowds in no doubt of Rome's dominion over the known world.

From the very beginning, no expense was spared to provide entertainment for the masses.

And the spectacle didn't stop there.

♪♪ Ancient writers suggest the inaugural games included an event even more extraordinary, one that demonstrated the empire's political, financial, and military might.

A show that would stretch Roman ingenuity to the limit.

In the heart of Rome, Darius Arya examines ancient texts that describe the first games held at the brand-new amphitheater.

-Take a look at this.

"For Titus suddenly filled this same theater with water and he brought in people on ships who engage in a sea fight there."

We're talking about ship battles in the Colosseum.

-This passage, from Roman historian Cassius Dio, was written more than 100 years after the inaugural games.

He never witnessed the event himself.

But naval battles had been acted out before on artificial lakes.

Could they really have been staged in an amphitheater?

-We're talking about flooding the largest arena in the ancient world!

It would have been a Herculean task to carry something like this out.

So how do they manage to do this?

-It would take extraordinary skill to build such a system.

A recent engineering investigation into the Colosseum reveals it might have been possible.

Researchers suggest large ducts that ran around the building's circumference fed into shallow channels that could have filled the arena.

Calculations based on their capacity prove that, if flooded, the arena could have then been drained in just a few hours.

-This sounds like an incredible challenge, but the Romans were masters in engineering and the manipulation of water.

-The Colosseum, as it is today, reveals no direct evidence that naval battles took place here.

Too much of its internal structure has collapsed, leaving researchers with many unanswered questions.

But the network of channels and the contemporary texts suggest that naval reenactments with scaled-down ships may well have been a reality.

♪♪ -Just imagine it -- now you have this huge arena of the Colosseum flooded with water, water, filled with ships, manned by sailors, with these ships ramming into each other and the sailors fighting each other to the death.

This is the kind of experience that would have made the Colosseum legendary.

♪♪ -But just 10 years after those first games, the Colosseum underwent an upgrade, adding infrastructure that would make spectacles even more extraordinary.

♪♪ -So, not long after Titus opens the Colosseum and there are the inaugural games, he dies and his brother Domitian takes over.

-The Flavians have been in power for a little over a decade.

And Domitian lacks the respect that his father, Vespasian, or brother, Titus, had.

He is keen to make his mark.

=One of the things Domitian pays attention to is the Colosseum.

Domitian is thinking about developments he can make to make the games more spectacular.

By throwing games that will keep the people entertained, he's making sure that they also see him as a good emperor and he remains popular.

[ Crowd cheering ] -During the games, emperors would shower the audience with gifts -- food, tokens for prizes, money.

Successful tactics to win the support of the Roman public.

Domitian went even further.

The games were hugely popular, so he added a fourth level to the Colosseum which made room for more than 10,000 additional spectators... and increased its height from 130 to almost 160 feet -- the equivalent of a 15-story building.

Not only did he expand the Colosseum to new heights, he dug down, creating the hypogeum, an underground chamber, a huge expanse beneath the arena floor.

It replaced any water control system that may once have been in place.

But how did this labyrinth of passages help entertain the crowds?

Federica descends into the belly of the Colosseum.

♪♪ The hypogeum is a maze of 14 corridors, lined with 32 small chambers.

In many places, the floors are marked by mysterious holes.

-[ Speaking Italian ] -Here we see a quadrangular block of travertine, in the center of which which there is a circular hole bordered by an enclosure, a metal structure that also bears a number.

-Within the walls that surround the holes, grooves and shapes in the stonework add to the mystery.

By examining all these features together, archaeologists have managed to reconstruct the intricate system.

The bronze inlay once held a wooden column that, when turned, would hoist a caged animal, or man, from a holding cell up to the arena floor.

♪♪ -[ Speaking Italian ] -These hatches opened suddenly, from which, just as suddenly, come out scared, hungry animals, ready to perform on the arena floor.

♪♪ -Emperor Domitian had transformed the area below the Colosseum into 130,000 square feet of high-tech stagecraft... ...the crowning glory of the greatest amphitheater in the Roman Empire.

[ Crowd cheering ] A magnificent venue for almost 60,000 people.

-The empire, in its sheer diversity, in its exotic, mesmerizing quality, comes to town.

And it comes to town first and foremost at the Colosseum.

-The Colosseum would continue to host thousands of games for the next 400 years... ...a showcase for the emperor to demonstrate his authority over the Roman populace.

♪♪ ♪♪ But when Rome falls to Barbarian invaders at the end of the 5th century, the Colosseum is on borrowed time.

-Rome remains an important city.

The Colosseum remains an important time-honored monument in the city of Rome.

But the empire is no more.

♪♪ -Without the empire, Rome can no longer afford the luxury of the Colosseum.

Written accounts reveal animal hunts and acrobatic displays were performed here in 523.

After that, the historical record is silent.

♪♪ But was this really the end?

Amongst the ancient trash excavated from the Colosseum sewers, the archaeologists make a discovery.

-[ Speaking Italian ] -When it arrived here, apart from the earthy incrustations, it did not present any type of corrosion, so it was in excellent condition.

♪♪ -It's a finely crafted ring of almost pure gold.

-[ Gasps ] Fantastico.

-The most special thing is that, inside, we found a small ball, probably in gold, which jingles inside this cage.

-Can I hear it?

-Yes.

We can hear it a little!

-But the golden ring presents a puzzle.

-The shape, the presence of this design, suggests it was made between the 6th and 7th centuries.

-Records state the games at the Colosseum ended by the early 6th century.

But if this ring was crafted later, a person of wealth was in the Colosseum long after the games finished.

Why were they there?

What were they watching?

♪♪ Questions for future archaeologists to answer.

♪♪ The Colosseum had hosted bloody entertainment for almost half a millennium.

[ Woman sobbing, lion growling ] [ Cheering ] It reflected the Golden Age of the Roman Empire.

But without the empire to pay for expenses, this once-great venue was abandoned.

Over the coming centuries, Rome herself would move on, returning to greatness as the center of Western Christianity.

And this new Rome found a way to repurpose the ancient monument.

-I'm standing in front of St.

Peter's Basilica.

This is the most famous church of the Roman Catholic world.

If you take a look at the balcony and then the rest of the facade, we see these beautifully articulated architectural features.

It's all the same creamy white limestone called travertine.

And it should look familiar.

We've got written documentation in the Renaissance of thousands of cartloads of travertine stone brought directly from the Colosseum to build St.

Peter's Basilica.

-The ultimate irony.

We think about the Colosseum, its bloodshed and its violence, and we have that grand arena for gladiatorial bouts living on, its stones transformed and reused as part of the heart of the new spiritual empire, the heart of the Catholic Church here in St.

Peter's.

-Not every stone was taken.

What remains is the ruin we see today.

Still standing almost 2,000 years later, it's a potent reminder of ancient Rome's bravado and brilliance... evidence of its cruel and callous culture... but an enduring symbol of an empire that once transformed the world.

♪♪