NARRATOR: It was a civilization of extraordinary ingenuity and inventiveness in every field-- including warfare.

But in ancient China, one weapon stood for power and prestige like no other.

The chariot.

JEFFREY RIEGEL: In order to be a superpower, you needed to be able to count your chariots in the tens of thousands.

NARRATOR: Now a major new excavation is helping to unlock the secrets of this ancient war machine.

(translated): We were excited beyond words.

NARRATOR: Clues hidden in the earth for nearly 3,000 years reveal the complexity of its construction.

Blimey!

That is a huge wheel!

NARRATOR: The changing tactics that helped it rule the battlefield.

MAN: Got him!

NARRATOR: And why it was so different from chariots in other parts of the world.

Thousands thundered across China's battlefields.

But how was the chariot really used in combat?

And how effective was it?

One way to find out is to bring a Chinese chariot back to life.

(rider yelling) (blade whirring) Now, expert craftsmen... HURFORD: It's not without its dangers, this game.

NARRATOR: ...engineers... (translated): We've finally made a successful piece today.

NARRATOR: ...and military historians.

MIKE LOADES: Inhabiting that space tells you how it should be used.

(echoing thud) NARRATOR: ...combine to build and battle-test a replica of a Chinese chariot.

HURFORD: Perfect fit.

NARRATOR: They'll decode engineering riddles hidden in this ancient military machine.

Investigate how it went from a high-status symbol to a weapon of all-out war.

And discover its impact on China's history.

(men yelling) ROBIN YATES: Without a doubt, chariots played a crucial role in the unification of China.

NARRATOR: "Chinese Chariot Revealed," right now on NOVA.

Major funding for NOVA is provided by the following... NARRATOR: The country we know today as China was once a mass of competing states, frequently at war.

The conflict between them created an ancient arms race as leaders battled to reign supreme, kingdoms rose and fell on the battlefield.

At the heart of this struggle was a weapon... ...that was prized more than any other... the chariot.

Yijie Zhuang is a landscape archaeologist who's been studying ancient Chinese society.

There are many, many archaeological sites all over China, and one thing that appeared time and time again were chariots.

So chariots definitely were a very crucial part of ancient societies thousands of years ago.

NARRATOR: Although we can gather clues about chariots in the texts of ancient scholars, as China historian Robin Yates has discovered, many mysteries remain.

They tell us generalizations, but they don't tell us exactly how they were used on the field of battle.

NARRATOR: Now, a new discovery in Hubei Province, Central China, in the town of Zaoyang, may help to answer some of these questions.

In 2002, a vast ancient cemetery about 200 times the size of a football field was discovered.

At the time, archaeologists were only able to unearth some of its treasures, leaving the rest buried.

But modern-day tomb robbers have targeted the site, so archaeologist Qin Fang has been called in for a rescue operation.

(translated): What a great day.

NARRATOR: It's a chance for the team to finish the work they'd started.

He and his colleagues have been slowly unearthing the rest of the cemetery's hidden treasures.

They've discovered 29 tombs, but one in particular stands out.

(translated): After archaeological surveying, we realized this was a large mausoleum.

NARRATOR: This tomb is larger than the others, but its original inhabitant is missing.

The skeleton appears to have been stolen.

Who was he?

Qin Fang excavates the remaining objects in the tomb.

QIN FANG (translated): I think it's possibly some kind of instrument, a musical instrument?

(men conversing) NARRATOR: Besides a bronze bell, there are more personal items, including precious pieces of jade.

QIN FANG (translated): Look, the carvings are really clear.

NARRATOR: Objects this valuable can only mean one thing: the person they were buried with must have been wealthy and powerful.

(translated): The owner of the tomb was a duke, a man of high status.

We were excited beyond words.

NARRATOR: Among the many artifacts, Qin Fang identifies a unique piece of pottery.

Its distinctive style and shape allows him to date the burial site to around 700 BC.

In early Chinese history, the first dynasties controlled an area between the Yangtze and the Yellow Rivers, much smaller than today's China and very divided.

YATES: At this time, China was not the unified nation that we know today.

The dynasty in power were the Zhou, and when the Zhou came to power, they divided the country into smaller states and ruled with relative peace.

NARRATOR: And the site also offers a clue as to which of the Zhou's many states the duke ruled.

On a bronze pot an inscription, "Zeng," so that suggests he was a wealthy aristocrat from the State of Zeng.

Historians believe it was a small, rather insignificant state surrounded by larger enemies.

Even though the Zhou ruled, over the centuries, the individual states would grow more powerful and started vying for control, constantly warring with each other.

The most important find at the site could also have played a key part in those struggles.

As they dig further, the archaeologists begin to notice subtle differences in the soil.

In some places, color changes suggest the outlines of mysterious objects.

They realize these shapes are the imprints left behind by ancient wooden structures, which have rotted away over the 2,700 years they've been buried.

(translated): Excavating is very challenging.

The wooden structure has long gone.

What's left is a hollow cavity, filled with soil.

So basically, we are tracing the soil inside the cavity.

NARRATOR: As they study the shapes, the site begins to make sense.

They identify the outline of what looks like a platform, and in the center an axle connected to two wheels.

There can be no mistaking it.

It's the ghostly remains of a chariot.

But the biggest surprise is yet to come.

There isn't just one chariot... QIN FANG (translated): We discovered a chariot pit of 28 chariots and a horse pit of 49 horses.

This discovery was beyond our imagination.

NARRATOR: Not one but a whole squadron of chariots is unearthed.

The layout of the tombs suggests the chariots belonged to the duke.

The color and texture of the soil indicates they were all buried at the same time.

The elaborate bronze wheel fittings are all that survive intact.

So many chariots must have cost an enormous amount.

Not to mention, the 49 horses buried alongside them.

QIN FANG (translated): These horses seem like a mess, but actually they are not.

Usually, you find two horses together.

These two are put together, so it looks like this pair horses pulled the same chariot.

NARRATOR: But why would he have buried them alongside his tomb?

Were they going to live on with their master?

YIJIE ZHUANG: The ancient Chinese believed they they can live a new life after their death.

So one of the things they often take into their afterlife were chariots because they believed that chariots can also guard them in warfare and fighting in the afterlife.

NARRATOR: Hiorian Jeffrey Riegel is an expert in ancient China.

He believes the chariot was a symbol of prestige that the Chinese would want to bring with them into the afterlife.

The chariots were so important that even after they died, they wanted to have their chariots with them so that the gods would recognize that these were important people.

The chariot was part of their identity; it represented their status; it was expressive of their power and their prestige.

NARRATOR: So the chariot was so important that leaders like the duke of Zeng invested a fortune in them.

But why?

Was it their performance on the battlefield?

Or were they simply elaborate status symbols?

One way to find out is to build a replica and test its true capabilities.

Two chariot experts have been granted special permission to visit the Zaoyang excavation.

Their goal is to carry out this experiment by bringing one of these chariots back to life.

Within a week, this excavation site will be covered over, so this will be their only chance to gather detailed evidence for themselves.

Military historian Mike Loades has tested chariots from across the world.

But he's never before been able to properly investigate a Chinese chariot.

All the ancient Chinese texts talk about the importance of the chariot, but they don't tell us how you actually fought in a chariot, and the only way to really find that out is to build one and do some field-testing with it.

NARRATOR: Expert coachbuilder Robert Hurford has 15 years' experience in building replicas, but this will be his first Chinese version.

I've got to get down in there and find measurements, get what little bits of evidence there are there.

This has to be battle ready-- can't wait to get on with it.

...clear delineations of lengths of axle and all of that.

NARRATOR: Mike and Robert's first job is to identify the best preserved chariot on which to base their replica.

LOADES: That wheel there is very clearly this wheel here and we can see from that that you've got the axle running across, you've got the pole, and that this square with the rounded corners, that's the platform.

So, this is a chariot.

NARRATOR: First, they need to measure each of the components.

While incomplete, these outlines will give them the basic plan they need for the build.

Exactly three feet.

Exactly three feet.

And now side to side... NARRATOR: Mike and Robert start with the box which encloses the platform where the crew would have stood.

I get 65 inches.

I mean, that width is colossal.

NARRATOR: It's far larger than most other ancient chariots they've seen.

Next, they turn their attention to the wheels.

The number of spokes immediately catches Robert's eye.

HURFORD: It's got many more spokes than we're used to having in chariots.

28 spokes.

NARRATOR: But it's not just the number of spokes that's unusual.

There's the matter of diameter as well.

HURFORD: Blimey.

We've got 56 inches.

Now, let's just put that in context.

Just stand that upright.

That is a huge wheel.

Yeah!

We've explored Assyrian chariots, Egyptian chariots, Hittite chariots... All of them, the wheels are down here.

Straight away, the wheels are completely different to anything else.

NARRATOR: The Chinese chariot's wheels are a third larger than those of Middle Eastern models.

And there are other differences too.

Chariots from ancient Egypt are much more compact and round at the front, with smaller, six-spoked wheels on an axle positioned at the rear.

The Chinese chariot is large and rectangular and has a central axle with giant, many-spoked wheels.

At first glance, it seems more like a cart than an agile war machine.

But why would the ancient Chinese builders have used this bigger design?

Mike and Robert think it might have been a way to cope with the tough landscapes of northern China.

The rough, grassy terrain was more challenging for a wheeled vehicle than the flat, sandy deserts of the Middle East.

On rough ground, small wheels fall further down between bumps, producing a jarring ride, while the larger Chinese wheels are able to resist the gaps, stabilizing the vehicle.

And the bigger wheels have a second advantage.

They act like a lever, meaning less energy is needed to pull the wheel over the bump, so it's easier for the horses.

The type of chariot discovered at the site played an important role in the wars during the Zhou dynasty.

With that in mind, Robert is eager to start building his own replica.

In his workshop in England, his first step is to create the rim of the chariot wheel using the ancient technique of steam bending.

HURFORD: It gives you a stronger result because the grain follows the shape that you want.

NARRATOR: The wood must be steamed to a critical temperature of 100 degrees centigrade or 212 degrees Fahrenheit.

The fibers become plastic at that temperature and so, you can bend it, and when it's cooled down, it sets hard so it retains the shape.

We've got to go quickly here; we don't want this to cool down.

NARRATOR: Once it's out of the steamer, they must bend the wood into shape within seconds or it will split and Robert will have to start again.

We're putting big pressures on this.

If it slips off, it'll fly back and I mean it could knock somebody's teeth out.

It's not without its dangers, this game.

(metal clangs) NARRATOR: Finally, danger averted, the rim takes shape.

The chariots at the Zaoyang excavation date to a turning point in Chinese history, around 700 BC.

When the Zhou dynasty had come to power in 1046 BC, they divided the land into regional states that remained unr their control.

But these states grew strong and rebelled.

As the Zhou clung precariously to power, war spread throughout ancient China as rival states attempted to conquer each other.

YATES: It's this time when chariots came into their own and we see larger and larger numbers of chariots on the field of battle.

The main text that tells us about how battles were fought is the Zuozhuan, and it describes the numbers of chariots that you find.

For example, here is one where the army has (reading classical Chinese), 700 chariots, and they are essential for success.

Here is another example where the general has gathered together 800 chariots and this is why this time period is called the golden age of the chariot.

(horses whinnying) NARRATOR: But did chariots always play this leading role in ancient Chinese battles?

How did they become such a prestigious and prominent weapon?

Clues can be found by looking in the ancient city of Anyang where the oldest chariots in China were discovered.

They date back 500 years before the Zaoyang chariots.

YATES: At that time, Anyang was the capital of the first recorded dynasty in Chinese history, the people known as the Shang.

And they had a glittering Bronze Age culture.

NARRATOR: These Shang dynasty chariots in Anyang date back to 1200 BC.

China historian Jonathan Clements and chariot expert Hsiao-yun Wu have come to examine these early chariots, starting with the wheels.

(translated): The Shang dynasty wheel that we can see here is very typical.

We can count the spokes, and there are 18.

Okay, so this is normal for the Shang dynasty.

NARRATOR: But the wheel was such a key component that designers kept improving it as the centuries passed.

(translated): The wheel technology gets better and better.

Once we move into the Zhou dynasty, the number of spokes increased from 18 to 28, 30 or more spokes.

NARRATOR: So the early wheel containing 18 spokes would transform over 500 years into a wheel with 28 spokes, just like the ones at the excavation site.

But why would Chinese builders have added these extra spokes?

(translated): This has a couple of benefits.

The first is that the materials became lighter, which allowed the chariot to move faster.

Also, more spokes increases the stability of the wheel.

CLEMENTS: It's like a kind of built-in redundancy that if you have more spokes, if you lose, one then you still have a full complement of spokes that keeps you rolling.

(shouting, horses whinnying) NARRATOR: So the engineering of the wheels evolved to make the machine perform better on the battlefield.

Did that mean the way the chariot was deployed changed as well?

Stored in the archives at Anyang Yinxu Museum is a curious artifact from the Shang dynasty.

Inscribed on an ancient tortoise shell, carved symbols provide evidence of the chariot's place in early Chinese history.

Jonathan Clements has come to meet expert Yuling He to see what the bones reveal.

So this is an oracle bone.

It is actually the scapula, the front of a tortoise's shell, and, in fact, what we have here is the earliest form of writing in China.

NARRATOR: The Shang kings heated shells or bones until they cracked and then interpreted these fracture lines to predict the future, whh they carved on the shell as symbols.

And one symbol in particular is very familiar.

CLEMENTS: You can actually see the word for chariot, it's a picture of what it is, it's a horse drawing a wheeled vehicle.

YULING HE (translated): On this day he asked the priest if he could order two people to fetch the right chariot.

NARRATOR: But there is something unusual about the way the chariot is depicted on the bones.

CLEMENTS: The strange thing with a lot of the oracle bones is when the word "chariot" turns up, it's slightly different every time.

It's like they're not sure how to spell it, because it's like a new word they don't use very often.

YATES: The chariot was a new invention and the Shang didn't really know how to use it effectively, so we don't really know whether it was used on the field of battle, or whether it was just a mobile command platform.

It wasn't as dominant a machine as it later became.

NARRATOR: So at first, under the Shang, it seems the chariot played a minor role in combat.

But over the centuries after their successors, the Zhou, came to power, the nature of warfare would change and the chariot would become more important in battle.

So the Zhou began to introduce technical innovations, which pose headaches for Robert.

In particular, making a wheel with 28 spokes causes a major problem.

The earliest Chinese chariots had only 18 spokes, which would have fit around the hub.

HURFORD: The earlier chariots used round spokes.

If you try to put 28 of these around this hub, you immediately find that there's no room for them.

So there must have been some sort of development in the design.

NARRATOR: The chariots at the Zaoyang excavation site were little more than imprints in the dirt, so details of how the pieces were put together were not preserved.

(car horn honking) The answer may lie with an extraordinary discovery from 2004-- a perfectly preserved Chinese chariot from close to the same time period, found during the widening of a canal.

(translated): The chariot was buried deeply and submerged in water, which created an environment without oxygen, meaning the wooden structure was fully preserved.

NARRATOR: Examining the intact wheel gives Robert the solution for adding more spokes.

In this chariot the spokes are flat, rather than round, meaning more can be fitted into the wheel hub.

And this chariot also reveals other secrets about how the ancient Chinese builders constructed the wheel.

(translated): The wheel was largely in one piece when we unearthed it, but when it dried out, many of the wooden pieces fell apart.

That's very handy because I need to find out how all these joints fitted together.

And if you've got pieces which have come apart, it's so much easier to see how they were put together in the first pla.

NARRATOR: During the preservation process, detailed photos were taken of the entire chariot.

They reveal that the wheels were constructed using a mortise and tenon joint, where a protrusion at the end of the spoke called a tenon fits into a slot in the wheel rim called a mortise.

This ancient joinery technique is used across the world, but there's something very distinctive about the way the Chinese chariot builders made this joint.

(translated): These are the original spokes from the chariot.

These are the tenons which are going into the rim of the wheel.

Two different lengths I see.

(translated): Yes.

Some of the tenons go all the way to the outer rim, and some only go halfway.

NARRATOR: Robert will need to work out the purpose of these two differently sized tenons.

HURFORD: This one will have to be marked out with great precision; and we still don't really know if it will work.

NARRATOR: As he builds, the reason for the different lengths of tenons becomes clear.

I think that is a way of making it easier to assemble the wheel.

I've got to draw these spokes round to line up with the holes.

You see how far out these are.

At least I don't have to worry about these two with short tenons for the time being.

It means that we're only wrestling half the number of spokes at any given time.

NARRATOR: If all the spokes had long tenons, it would be impossible to fit them into the rim.

HURFORD: Got it.

NARRATOR: With the long tenons in place, the short ones can easily slide in.

It's quite ingenious, really.

NARRATOR: With the wheel complete, Robert can now focus on other details.

In the chariot pit at the Zaoyang excavation, the wheels were accompanied by a series of bronze hub fittings.

They tell us precisely what the wheel hub was like, and it's extremely long.

NARRATOR: The length of the wheel hub was critical to the design of the chariot.

The hub is hollow and fits over the axle.

To reduce friction, there are a few millimeters of clearance between the axle and the hub.

If the hub were short, this clearance would cause the wheel to oscillate.

But by having a long wheel hub, the unwanted movement is reduced.

The wheel hub also bears the weight of the chariot, so adding bronze rings further stabilizes the wheels.

That's the one against the chariot body.

NARRATOR: Laying the bronzes out, a clue as to how they might have been produced is hidden in the smallest of the fittings.

And, finally, the axle cap with its lynchpin.

It stops the wheel falling off.

HURFORD: The lynchpin.

It's a small thing, yet it's so intricate.

Do you see along the middle there there's a little seam?

There is.

And in there another little seam.

It's been several piec, this, in a mold.

NARRATOR: The seams reveal that the bronze pieces were made in a mold.

A foundry in Tianjin near Beijing is recreating the bronze fittings for the replica.

The first item to be cast is the axle cap, which would have sat at the end of the axle with the lynchpin and held the wheel in place.

Jinchao Wang from Nanjing Museum is an expert in historical crafts and has studied the way ancient Chinese metallurgists cast bronze.

He shows how they used clay molds made in several different pieces.

(translated): We put the inner mold together with the outer mold.

Once they are together there is a space between the two, through which the molten metal can flow.

NARRATOR: The molds are joined together and encased in clay, ready to receive the molten metal.

This method hasn't been practiced for hundreds of years, so for Professor Wang, this is a critical moment.

This step is the most important-- pouring the molten metal inside.

(sizzling) NARRATOR: It's immediately clear that there's a problem.

JINCHAO WANG (translated): The surface is rough.

LUO BAOQI (translated): Yes, because of the steam.

NARRATOR: The high moisture levels in the clay produced so much steam that bubbles formed in the metal.

(translated): The steam should have escaped, but it just remained inside.

NARRATOR: With a limited number of molds, they can't make the same mistake again.

The clay is dried to reduce the moisture and they go for a second attempt.

This time it works.

JINCHAO WANG (translated): After several tries, we've finally made a successful piece today.

NARRATOR: And they are also successful when they make the pin.

These bronzes also include the seam that Robert first noticed on the ancient bronzes from the excavation, created where the molds were joined together.

(translated): This line is the seam between the molds.

This is the key evidence that shows this bronze was cast using the clay technique.

Because of the high value of bronze back then, people would use as much bronze as possible to decorate their chariots.

That's the reason why we find so many bronze decorations in these excavations.

NARRATOR: Now that the bronze pieces from the Zaoyang site have been successfully recreated, Robert returns to the preserved wooden chariot for crucial details about the main frame of the box.

HURFORD: It's fascinating.

So we've got one piece of wood very tightly bent on this corner and that's our framework.

NARRATOR: If the corners were built from two pieces of wood joined together, they would cause weakness to the structure.

So the ancient Chinese builders used solid pieces of curved or bent wood at the corners to create the final shape.

Steam bending couldn't achieve such a tight bend.

Instead Robert thinks the solution may lie in the natural landscape.

This is a naturally bent branch.

There's a lot of natural strength in that shape.

It's what you call a grown bend.

And I'm sure that's how the ancients would have done it.

NARRATOR: Robert is replicating the techniques of the Chinese chariot builders by using a naturally bent piece of wood to form the corner of the railing for the box.

You can see the grain following around the shape of the timber here.

So that's as strong a piece of timber in that shape as we can find.

NARRATOR: He glues the pieces together on the straight section to make as strong a joint as he can.

Something which was impossible to bend in the flat we've made into an item that we can use in this chariot.

NARRATOR: Robert is starting to assemble the major components of the chariot-- the wheels, the pole which connects to the horses, and the box.

The positioning of the box centrally over the axle is one of the defining characteristics of the Chinese chariot.

Robert is more accustomed to making Middle Eastern chariots, such as those used by the pharaohs of Egypt, where the axle was positioned at the rear.

In that design, the center of gravity of the box is suspended between the axle and the horses.

This made the structure springy, adding an element of suspension.

That system improves the smoothness of the ride.

So why didn't the Chinese chariot adopt this technique as well?

It turns out that the Middle Eastern configuration has a drawback-- it puts more weight on the horses' necks.

By putting the load right over the axle, the Chinese chariot and its load can be heavier, and the reason it needed to be able to carry more weight is revealed in ancient texts.

The Chinese war chariot was unlike war chariots in the West.

It was designed for a crew of three, not of two.

And we can see this in the writing of the military expert Sun Bin.

(reading Chinese text) "The one who is good at archery is on the left.

"A good driver is the one in the middle.

And one who has no particular ability is on the right."

NARRATOR: But just how effectively could they fight in such cramped quarters?

And what was the role of the third person on the right of the driver and archer?

It's one of the key questions that testing the replica chariot will help to settle.

Robert is pushing to get the chariot finished so testing can begin.

The base of the floor will be woven rattan, a lightweight and flexible traditional material.

There's a fair bit of give in this, but I think that may give a nice little bit of bounce to the floor, so the floor, in fact, is more comfortable to stand on.

NARRATOR: Flakes of red paint found at the Zaoyang excavation were used to recreate the way an ancient chariot appeared.

HURFORD: The color is very important in our chariot here because this chariot is a big statement of visual effect, so it's not just a decoration.

NARRATOR: And the polished bronze wheel fittings have arrived from China.

HURFORD: Doesn't it just make a huge impact?

It also does a job.

It's stopping the end of the hub from splitting.

There we are, perfect fit.

NARRATOR: The replica chariot is almost ready for testing, a process that could provide an insight into the chariot's role in battle.

There's still a big debate about how effective the chariot was.

Some scholars argue that it was like a tank, it was very effective.

And others argue that it was very fragile.

It could be easily broken.

YIJIE ZHUANG: There were different ideas about how the chariot was used in battle.

For some scholars, chariots were used in the middle of very brutal battles, whereas other scholars think the chariot was more a command post situated at the outskirts of the battle.

But actually no one really is sure how exactly the chariot was used in battle.

NARRATOR: And even the ancient military texts give conflicting accounts of the chariots' effectiveness.

The military strategist Sun Bin, who lived around 300 BC, describes their strengths and weaknesses.

YATES: This is Sun Bin's Art of War.

"Where the terrain is flat, the advantage belongs to the chariots."

(reading the text) "On difficult ground, that's advantageous for infantry."

You can see that sometimes the chariots had the advantage and sometimes the infantry, so it's very difficult to decide whether or not chariots really had a tactical advantage in a large battle.

NARRATOR: Now, some of these questions can be tested.

After more than 200 hours under construction, a Chinese chariot from 700 BC, their golden age, rolls into action.

Using measurements taken from the ancient skeletons, the team has chosen a powerful pair of horses, similar in stature to the horses that would have pulled the original chariots.

And the most important feature-- its giant, multi-spoked wheels-- are ready for testing.

By the time the chariots at the Zaoyang excavation site were buried, in 700 BC, the Zhou dynasty was losing control of their regional states.

Smaller, weaker states were being conquered and absorbed by richer and more powerful neighbors.

Many had succumbed on the battlefield, where the chariot was more prolific than ever.

But exactly what role did the chariot play in these battles?

The first step is to discover how well a crew could function in a chariot box.

Mike's first test is to explore the role of the archer, positioned on the left of the box.

He sets up some targets to represent enemy troops.

LOADES: It's the driver's job to position the chariot so the archer can get off his shots.

But I want to find out how well can an archer operate, because if the archer can't operate, then it's just a parade vehicle.

We have to see how it works as a weaponized vehicle.

NARRATOR: The Chinese chariot would have normally carried three warriors, but to get accustomed to shooting from this platform, Mike is accompanied by only a driver.

The box's low sides would have offered little support to the men if they stood upright.

So Mike explores another possibility: that the archer could have operated in a crouching position.

Inhabiting that space almost tells you how it should be used.

NARRATOR: The design makes practical sense.

On a bumpy battlefield, staying low would have kept the archer safely on board, keeping his shot steady while reducing his profile as a target.

Ancient military writer T'ai-kung, looking back on this time, described how chariots were also accompanied by a team of foot soldiers.

Staying in formation was important, so the chariot needed to travel quickly enough to maximize the impact of the archer without leaving behind the men on foot.

Each chariot is supported by infantry.

Infantry squadrons ran with the chariots.

I think that alone tells us the chariot probably operated at the trot.

Okay, bring them back to the trot.

NARRATOR: Trotting allowed the foot soldiers to keep up but also helped the archer.

That steady trot enables the archer to get off more arrows.

There's no point in galloping around there and shooting one arrow.

That steady trot, we're decimating these men.

NARRATOR: But why did the Chinese choose to add a third man to the crew, especially given that the added weight made it necessary to build a larger machine?

The answer is because the third team member also carried an important weapon... A combination of a dagger axe and a spear, known as a ji.

Among the bronze arrowheads found at the Zaoyang excavation site, spearheads were also discovered.

The team adds a third man, who attempts to use a ji from the chariot.

LOADES: And we'll build up the speed, see what we can do a little bit.

It's not a natural weapon for the chariot, is it?

GORDON SUMMERS: It certainly had the reach, but it's a tight space to be operating a relatively cumbersome weapon.

NARRATOR: The spear seems just too long to use from such a confined space, so perhaps it had another function-- defense.

What about if we're stuck like we are now and we've got infantry coming from behind us?

Yeah, if we are stuck in a melee, then I can use its length and I have a fairly good reach in all planes.

Because that's what you are, really, on the chariot team.

Your primary job is to defend us.

NARRATOR: But how were chariots deployed on the battlefield?

At first, chariot fighting was a highly ritualized activity.

YATES: Chariot warfare was conducted by nobles and fighting was done according to a code of chivalry, something similar to the knights of the Middle Ages.

It really was a platform for the nobles to show their ability to behave and fight in the correct ritual way.

NARRATOR: Early battles took place at designated times and locations, and generals complied with strict laws of combat, including a rule which forbade a warrior to kill an enemy of higher rank.

But eventually chivalry gave way to all-out war.

The pivotal Battle of Chengpu, fought in 632 BC between the state of Chu and the state of Jin, featured the first well-organized and highly professional armies.

Described in the Zuozhuan, an ancient text which charts the history of this period, the two armies fielded around 800 chariots each.

Using these chariots, the Jin army demolished part of the Chu army, scattering their troops.

The Jin then faked a retreat and, cleverly, using their chariots to create a dust cloud, obscured the view of the pursuing Chu forces.

At that point the Jin army, joined by their chariots, sealed their victory over the Chu.

And although the numbers of chariots involved at Chengpu was relatively modest, this would not be the case for much longer.

As fighting intensified, what mattered was victory at all costs.

It didn't matter how you fought.

What mattered was that you defeated the enemy.

NARRATOR: Just a century later, ancient texts reveal that the states of Jin and Chu each fielded at least 4,000 chariots, five times more than before.

And that was just the beginning.

RIEGEL: There emerged a kind of hierarchy that was determined by how many chariots you possessed.

In order to be a superpower, in order to guarantee victory, you needed to be able to count your chariots in the tens of thousands.

NARRATOR: The growing size of the chariot forces made the choice of where to fight crucial.

YIJIE ZHUANG: One of the most important things for the commanders who wanted to use chariots in their battles is to consider the condition of the terrains, which includes a wide range of different, sometimes difficult terrains.

NARRATOR: Yijie Zhuang is visiting a landscape in modern Tianzhen county in northern China.

This region was much fought over in ancient China.

So look at this very unique landscape.

At the far end were the mountains linking the central plains with the Eurasian Steppes, whereas in the middle are flat, very wide and open plains.

This would have been the perfect place for a chariot battle.

NARRATOR: Although this land is now covered in crops, hedges, and trees, the land underneath is flat and would have been similar to the test field in England.

To assess how steady the ride would be, Mike tests the chariot under ideal conditions on the flat field.

LOADES: There's no doubt about it, it is a bone shaker.

The wheels may be big, but they're still solid and they're on a solid axle, so it's a very jarring ride.

But the ponies are pulling this along at a fair lick and with tremendous maneuverability.

This thing is spinning on its own axis.

NARRATOR: But the maneuverability of the chariot couldn't get it past every obstacle.

Ancient writers specified the terrains chariots should not be used on, including ravines and ditches, high mounds and sharp hills.

And this advice became ever more important as the scale of the battles grew and the regional states conquered each other.

Now, after eight centuries of struggle, just seven states remained, growing ever larger, richer, and more territorial.

It meant leaders were forced to take their chariots further afield and face more difficult terrain, limiting their ability to use them.

And blocking enemy chariots became a defensive tactic.

YIJIE ZHUANG: The regional leaders, they were building a lot of walls like this one, which created barriers for the chariot to move around.

So this divided territorial landscape has become incredibly difficult for chariots.

NARRATOR: The chariot was being stretched to its limits.

And by the time the Zhou dynasty finally collapsed, a more versatile military unit had begun to make itself felt-- the cavalry.

Traditionally, war horses in China had only been used for pulling vehicles, not widely for riding.

This changed from around 500 BC, when states battling with tribes from Mongolia began adopting their enemy's tactics of riding horses.

The rise of cavalry and horse-mounted archers soon challenged the chariot's dominance.

To see just how much more agile the ridden horse is, Mike tests how a mounted archer would fare against a chariot.

The chariot is capable of impressively swift, tight turns.

(horse whinnying) But can it survive an assault by a well-trained horse and rider?

Riding as a horse archer against the chariot, I felt I had the complete advantage.

I was more nimble, more agile, I was faster.

Once the horse archer is present, the chariot just cannot compete.

NARRATOR: More flexible over tough terrain, cheaper, and easier to deploy in great numbers, the new cavalry forces would soon eclipse the chariot on the battlefield.

Another factor was the sheer size of the contending armies.

From around the fifth century BC, the land we know as China entered the Iron Age.

Farmers now had iron tools, leading to a population explosion.

Iron technology was abundantly used in agricultural production, and together with the construction of very large scale irrigation projects, they can grow more food and therefore they were able to support more population.

NARRATOR: A larger population meant more people could be drafted onto the battlefields.

RIEGEL: Being able to put a large army into the field, an army not simply of tens of thousands, but literally of hundreds of thousands was crucial.

NARRATOR: And one state would become particularly famous for its massive armies-- the state of Chin.

It was Chin that would eventually defeat all other surviving states, finally unifying China under one emperor and one name.

The Chin still used chariots, but they also mixed in cavalry with them as well as infantry.

So by the time of the Chin, the era of the chariot was over.

NARRATOR: Although the golden age of the chariot was past, its role in the centuries of battle, which saw the many states struggle for dominance, meant this machine had played its part in creating the nation of China.

YATES: It's clear that the chariot played an important role in the warfare that led to the unification of China.

Without the chariot, I think that China could not have been unified.

NARRATOR: The chariot was no longer dominant on the frontline of battle, but it remained a powerful symbol.

The glory and prestige of centuries of warfare had ensured its place at the heart of Chinese civilization.

And a fitting tribute can be seen in the tomb of China's first emperor, Qin Shi Huang.

Along with the famous Terra Cotta Warriors, he was buried with a pair of breathtaking bronze chariots.

YIJIE ZHUANG: Many cultures in the world have chariots, but for the ancient Chinese, chariots were very special.

They used chariots to showcase their power and prestige.

NARRATOR: Through building and testing the chariot, the team has gained a telling insight into why it was so highly revered by the ancient Chinese.

LOADES: You imagine them in their hundreds, in their thousands, that noise, that clatter.

It was the state-of-the-art technology of its day.

Its day passed, but in its time, this was the best military vehicle possible.

RIEGEL: Their chariots had become part of their culture, part of their heritage, part of their identity, to the extent that even given the limitations of the machine, they couldn't imagine going anywhere without them.

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