Original subtitles

It's China's most stunning palace.

The Forbidden City.

The greatest wonder of the medieval world.

And the biggest wooden structure on earth.

It's the largest complex of palace buildings anywhere in the world.

Home to the China's emperors,

a place of staggering wealth and power,

filled with dazzling treasures.

Only the Emperor could pass along the central line.

It was closed to the outside world for centuries.

Now, our cameras have been given access behind the palace gates,

and scientists set out to solve the enduring mysteries

of this engineering marvel.

How was this epic mega-structure created?

Who built it?

And how has it survived 600 years of war,

upheavals and natural disaster?

Maybe we'll take one step back.

The secrets of the Forbidden City can finally be revealed.

The Forbidden City is a wooden wonder.

History's ultimate mega-structure.

Dominating the heart of Beijing,

it boasts a staggering 900 buildings.

Opened in 1420, it is a pleasure palace,

an impregnable fortress

and a seat of immense power.

The most important site in the whole of Asia for the last 500 years.

Economically important, politically important and militarily important.

The main entry is the Wumen, or Meridian Gate,

leading into the spectacular outer court,

with its five marble bridges that cross the man-made Golden River.

The Forbidden City is 10 times the size of Versailles.

This is the largest palace complex in the world.

And not just the largest palace complex that survives,

but the largest palace complex built at any time in history.

Architectural historian Jonathan Dugdale wants to master its layout.

Up ahead is the Gate of Supreme Harmony.

And if you think that's impressive,

wait till you see what's on the other side.

Three great halls dominate the outer court,

towering over a three-tiered marble terrace.

Beyond is the inner court where the Emperor lived.

It all covers 178 acres...

..with the outer court to the south

and the inner court to the north.

Forbidden to any man but the Emperor or his sons,

with hundreds of structures.

All surrounded by fortifications and a moat 50 metres wide.

The Forbidden City originally contained 9,999 rooms.

One less than the divine number of 10,000,

reserved for heaven.

It boasted scores of temples, gardens

and the Emperor's vast harem...

..with thousands of concubines and an army of eunuch guards.

A hotbed of decadence and betrayal.

But above all, a centre power.

But at its heart, there is a mystery.

In a time before industrial technology,

how did a medieval society produce such a marvel?

No original plans or blueprints survive.

So there is no record of how it was created.

To find the answer,

we've gone behind closed doors

to its workshops and new research labs,

with special access to its scientists and master craftsmen...

..to understand the palace and the medieval superpower who built it...

..the Ming Dynasty.

From 1368, they ruled China for nearly 300 years.

The Forbidden City is all the creation of one brilliant

and terrifying Ming emperor...

..Yongle.

Warrior,

scholar,

mass murder.

The Yongle Emperor is one of the greatest emperors in Chinese history.

Without him, China would be completely different.

You simply would not have had a Forbidden City that we see today.

But Yongle was never supposed to be Emperor.

In 1402, he took the throne by force...

..after waging a brutal civil war against his nephew,

the Jianwen Emperor.

It was a matter of life and death.

He either rebelled and seized the throne

or he would have been eliminated himself.

Yongle stormed the first Ming capital, Nanjing...

..and left it in flames.

The Jianwen Emperor disappeared.

We do not know what happened to him.

But bodies...were found,

burnt beyond recognition.

Yongle burnt Nanjing and declared

he would build a new northern capital,

1,000 kilometres away.

Beijing.

Yongle was a driven man, an ambitious man.

And he was ruthless.

He eliminated tens of thousands of officials.

By building the Forbidden City at the heart of his new capital,

the new Emperor would create a dazzling display of power.

His ambition is reflected in its sheer scale.

Without his vision, of making this as a capital,

China would simply not have

the central role that it does in the modern world today.

It's a vision of one man,

but it's actually the genius of the entire Chinese people.

So vast, its construction even shaped the landscape itself.

This hill gives us an amazing aerial view of the Forbidden City.

What's more incredible is that, prior to the construction,

this hill didn't even exist.

It was actually built using the earth excavated from the moat.

Building on such an epic scale faced huge obstacles.

The environment and the climate was bad,

they still suffered from floods and famines here and plagues of locusts.

So all of this was an enormous undertaking.

All the labour and materials had to be brought to Beijing.

Today, the fruits of that labour can be seen up close

in structures such as the Taimiao Temple.

It was first built in 1420 by Yongle to honour his ancestors.

Yongle came to this spectacular temple

to assert his connection with his predecessors in the Ming Dynasty.

The importance of Taimiao

is reflected in its vast size and ornate decoration.

The 30-metre-tall columns sparkle as if speckled with gold.

It's a chance for master carpenter Richard Wiborg

to see a rare Ming interior up close.

Look at this magnificent column. So round and so smooth.

Imagine how big the tree was that this came from.

In fact, we have 68 columns in total for this hall.

And they are supporting the structure.

And they look beautiful as well.

This is a single log of a nanmu tree,

the rarest of all Chinese woods.

It's straight, dense and resistant to rot.

But nanmu can only be found deep in forests

over 1,800km from Beijing.

And the sheer quantity of wood required is staggering.

The latest hi-tech laser scans show the Forbidden City's biggest hall

contains thousands of timbers.

The roof area alone is revealed as a forest of complex beams,

joints and trusses.

Above, the huge roofs are covered with thousands

of heavy glazed tiles and figurines.

This amazing edifice in front of us

brings up a huge number of questions.

How did they build it?

Where did the resources come from to create something so vast?

To supply this vast building site,

huge quantities of specialised materials

were imported from across the whole empire.

Over 100,000 nanmu logs from 1,800km to the south west.

Golden floor tiles from 1,000 kilometres south.

80 million bricks, each weighing 24kg.

Gold leaf from Nanjing.

And food for the million workers and vast garrison.

But to get everything to Beijing,

Yongle's builders had to dream up another engineering marvel.

China's Grand Canal.

The Grand Canal

is both longer and older

than the Panama Canal

and the Suez Canal.

They really solved a very large problem

of canal engineering at the time.

Rebuilding a canal that runs over 1,700km.

From commercial Hangzhou in the south,

it then links China's lifeblood rivers,

the Yangtze and the Yellow.

Right up to Beijing.

The water flow is controlled from Nanwang.

Here we are

at the centre of the Nanwang water diversion project,

part of the Grand Canal system.

Here at Nanwang, the whole river was diverted to feed the canal.

Today, it is dry.

But this is what it would have looked like in Yongle's reign.

But the hilly terrain blocked the canal,

so engineers devised a vast system of locks.

To raise the ships, the canal is fed from the one river.

And three huge lakes were dug as storage tanks.

Barges travel up the canal to Nanwang,

where they enter a series of locks over 5km long.

The river water pours in to raise the ships in the lock

so they can then proceed.

Huge sluices then empty the water into the specially made lakes,

ready for the next vessels.

For just this section of the canal,

there were 300,000 labourers conscripted,

working for a period of 200 days constantly.

And they created this with only the most rudimentary hand tools.

The Grand Canal allowed engineers to float the nanmu logs

north to Beijing.

Along with a fleet of 20,000 barges,

manned by the Army, to carry 420 million litres of grain

to feed the Beijing building site every year.

The cost was paid by Yongle's subjects

in money, materials and lives.

Tens of thousands of people starved to death.

He worked convicts, he worked the military,

he worked ordinary peasants.

He squeezed as much as he could out of the taxes.

Their sacrifice was building a palace unrivalled anywhere on earth.

But what was going on behind the opulent walls of the Forbidden City?

For a man who stole the throne -

Ming emperor, Yongle.

A typical day in Yongle's life could cover much of his private city...

..the Great Within.

This courtyard and the palace behind me is the most sacred

location in the entire Forbidden City.

The Palace of Heavenly Purity.

And every morning he would rise at about four o'clock

and he would come down this central pathway,

only he could pass along the central line,

for the dawn audience.

At dawn, thousands of eunuch mandarins would gather here

in silence.

To kowtow before His Majesty.

Filling the courtyard in front of the city's grandest structure -

The Hall of Supreme Harmony.

In the very centre is the throne.

On either side you can see dragons and the dragons have five claws.

That is the Imperial dragon, only the emperor could

have five-clawed dragons.

And above, you have the symbol of the heavens.

And the throne is directly underneath the heaven.

Why? Because the emperor is the son of heaven.

Yongle must constantly prove he has the mandate of heaven.

And demonstrate he is worthy to rule, by maintaining a careful

balance in the cosmos, through daily rituals and ceremonies.

One of which was ensuring the safety of the palace.

The Yongle Emperor would have come out from this gate here

in his private quarters, walk down these steps

and probably, if it was winter, he would have come to these

great cauldrons, which are now brass, but originally

covered in gold leaf, and put his hand inside,

to make sure that there was no ice.

They must be full of water, as these are the Forbidden City's

fire extinguishers.

In a wooden palace, any spark can lead to disaster.

But the Forbidden City is not only made from wood.

Many of the key halls and palaces sit on layers of

marble terracing.

Huge blocks, quarried over 60km outside Beijing.

One of the city's most impressive features is

Emperor Yongle's Grand Staircase.

Inlaid with dragons.

Hand-carved from a single vast block of the finest marble,

more than 16 metres long.

It weighs over 300 tonnes, more than 125 Land Rovers.

It's the largest stone structure in the Forbidden City,

showing nine dragons playing in the clouds.

Just touching them led to a death penalty.

But how was it transported from the quarry over 60km away?

Scientists are investigating a new theory

that might explain how it got from the quarry to the

Forbidden City.

Every winter, Beijing freezes over and Ming court records

describe the creation of great ice roads.

Modern science suggests they may have moved the blocks...

on ice.

Professor Rob Dwyer-Joyce is a tribologist -

a friction and lubrication engineer.

He wants to discover how many men would be needed to shift the marble.

What we have is a wooden sled, we've loaded it with stone

weighing about a tonne, 1,000kgs,

or 2,200lbs and we're going to do an experiment to try

to pull this along by hand on the ice.

This is gonna be quite difficult cos it's...

ALL STRAIN

No, we can't get it shifted.

No, can't do it. I think we're gonna need some help.

Even a whole ice hockey team struggle to get it moving.

Whoa!

So, how much force does it take to start a one-tonne sled

sliding across the ice?

Remembering that the marble block of the Forbidden City's

grand dragon stairs weighs 300 tonnes.

The challenge is to get it started.

Ming sources say wells were dug along these ice roads,

could water help get it going?

I'm gonna put some water down there, to see how

many we need when we've slightly wetted the ice.

Go on, pull, guys.

The water acts as a lubricant, making the sled easier to start

moving over the ice.

This is exactly what happens with an ice skater's blade.

The friction creates a very thin layer of water between

the blade and the ice, allowing grace and movement.

The Ming dug the wells every 500 metres, to create the ice road

and then lubricate it.

Scaled-up, our experiment proves just 180 men could move

the 300-tonne marble block.

And it wasn't just the marble that had to brought over great distances.

What strikes visitors, along with the Forbidden City's

sheer scale, is the vast array of colours -

the turquoise, blues and greens.

Now, new evidence is emerging of efforts made to source

the very best materials.

At the Hall of Mental Cultivation, the doctor's restoration team

are working to identify the precise pigments used to colour the paints.

Over the centuries, layer upon layer of paint has built up.

Making the task of identifying the minerals very difficult.

HE SPEAKS OWN LANGUAGE

They are using the latest technology -

a portable X-ray fluorescent spectrometer,

to make some startling discoveries.

At his lab, the doctor combines the XRF scan data

with the microscopic examination of paint fragments,

to identify the colourful elements.

Shi qing is made by grinding down the mineral ore - azurite.

But this doesn't look like azurite.

His analysis identifies the compound.

It's a remarkable find.

This blue is smalt

and only comes from Europe.

Further analysis shows the pigments used to create

the Paris green and ultramarine paints

are also unique to Europe.

The analysis ensures the correct pigments are

used in the restoration

but also proves that to decorate the Forbidden City

no expense was spared.

In all, it took over one million labourers

to build Yongle's Forbidden City

and over 100,000 skilled craftsmen and carpenters

from across the empire,

to build a wooden structure unsurpassed in scale,

even to this day.

But once built, how did the palace survive

nature's most devastating force -

earthquakes?

In December 1420, Emperor Yongle's Forbidden City was complete.

His vast palace was ready to face the world.

Diplomats and dignitaries arrived for its grand opening ceremony.

They are overwhelmed by just the physical space.

This statement of power, political power, the power of the dynasty

but also the power of the emperor.

Visiting ambassadors describe 300,000 guests,

2,000 musicians and dancers, and as many armed guards.

This constant visual campaign of political persuasion that -

"I am the most powerful man in the world."

Now it was complete, the Forbidden City became the beating heart

of the Ming dynasty.

The place where the Emperor Yongle lived

and the headquarters from which he commanded his empire.

But over the centuries,

his palace has faced a series of man-made threats -

revolution, civil war and invasion.

But one of the greatest threats of all was natural disaster.

RUMBLING

Beijing sits in a very active seismic zone.

With dangerous fault lines that spread over 1,000km.

HE SPEAKS OWN LANGUAGE

Dr Jo is the Forbidden City's resident seismologist.

In its 600 years, the Forbidden City has withstood over

200 devastating quakes.

Including the deadliest earthquake of the 20th century.

In 1976, centred around 150km east of the capital...

..it was magnitude 7.8.

In just 15 seconds, it killed 250,000 people.

Tangshan city was obliterated.

So how has the Forbidden City survived so many quakes?

To find the answer, specialist carpenters are building

a unique scale model to replicate

the classic Forbidden City structure.

To be as accurate as possible, it is being made using

traditional carpentry tools and techniques -

the scale is one to five.

A fifth of the original size,

engineers have built it on a shake table,

to simulate earthquake forces,

calibrated to the size and weight of the scale model.

The scale model is based on the traditional timber-frame core,

as used at the Palace of Longevity and Health.

What you immediately notice is this huge golden roof

and it curves outward away from the building

in a way that you just don't see in European architecture.

Looking up here, what we have is these elegantly coloured

cross beams, decorated with Imperial dragons and phoenixes.

And they are there to support these huge red columns

that bear the structural load of that massive roof.

These beams and columns are the structural core of all

the Forbidden City's buildings.

If you look up here, in between the cross beams and the roof,

underneath that mesh, there's these flower-shaped brackets

and they are called dougong.

A dougong is a complex bracket that supports the huge roof.

At first glance, it looks like an elaborate decorative feature.

But the unique design is the structural key to

every Forbidden City building.

Dougong brackets are extremely versatile,

they've been used throughout East Asian architecture

for literally thousands of years.

We see examples of them used in Buddhist temples,

palatial architecture, down to simple houses.

Dougong date back at least 2,000 years

but they reached their zenith in the Forbidden City.

Carpenter Richard Weiborg finds it's easy to take one apart.

But harder to assemble.

Now, after taking a deep breath, we'll try and put

this back together again.

And amazingly, there are no nails or glue,

nothing holding it together, other than sheer ingenuity.

You can see this isn't - even for somebody who has done it

a few times - it's complicated.

One piece goes in the front here.

There you have it, a bracket set.

So, you can see, it's a little bit flexible.

It's very strong, pressing down it can take a tremendous

amount of weight.

It ties together with other parts of the building

and is a beautiful creative feature of Chinese architecture.

The complicated dougong brackets extend to the exterior,

to support the eaves as well as the roof.

They sit on the large beams, supported by the tall columns.

But the columns are not founded in the earth,

and are free-standing.

All these structural parts bear the roof's immense weight.

For a large hall, it is 1,800 tonnes.

Engineers highlight areas that are vulnerable during

the most powerful quakes.

The earth's movement could snap the columns,

fracture the beams or joints

or topple the roof.

It seems a tremor would be catastrophic,

so how does it survive quakes?

CRASHING

Now, in series of unique tests, the Forbidden City's seismologist,

Dr Jo, will subject the scale model to a series of

simulated quakes to discover how the Forbidden City's intricate

parts react and see what magnitude of quake they can survive.

It's test day.

Wow, the roof is so big.

It's amazing.

Dr Jo is joined by Richard Weiborg.

The shake table will replicate the energy of quakes

in increasing orders of magnitude.

How strong a quake will it take to bring down the structure?

An earthquake's strength is defined by its magnitude -

the amount of energy released.

Each tremor lasts 30 seconds.

As the magnitude rises, 4.0, 4.5...

then 5.0...

These are massive increases.

A magnitude 5.0 has ten times the energy of a 4.0.

It begins to strain the dougong.

LOUD CREAKING

Maybe we'll take one step back?

Magnitude 7.5 is over 1,000 times stronger

than the initial test quake of 4.0.

There it goes...

That was pretty exciting.

Yes.

This shows that the brick walls have no structural role.

And the timber frame does all the work.

LOUD CREAKING AND RUMBLING

But how long can the frame resist the force of nature?

So, a 9.0, this is like a very, very big earthquake.

The test now moves beyond magnitude 9.5,

the largest recorded quake in history.

The equivalent energy to well over two billion tonnes of TNT.

LOUD CREAKING

We wanted to break this building and it wouldn't break.

So, wonderful test.

When Dr Jo and Richard examine the model,

they find clues to how it survived the quakes.

This explains why the columns are not founded

deep into the stone bases -

if they were, they could only break

if overwhelmed by the energy of the quake.

By being left free to move, they ride out the earthquake.

The design secret can be summarised in one word -

flexibility.

The wooden parts work both as individual units

and together.

The dougong acts like a shock absorber in a car

and there's both friction and rotation

that absorbs the energy from the earthquake.

The test also explains the effect of the heavy roof.

It acts as counterweight, pushing down so the flexible parts

can ride the quake.

What was most surprising to me was how much the building

can move, how flexible it was.

Nothing was damaged and it can survive a 10.1 earthquake.

This is a fabulous proof of the genius of

Chinese traditional architecture.

It has allowed the Forbidden City to survive

one great force of nature...

..but there was one enemy it couldn't resist for ever...

Not earthquakes...

but fire.

For nearly 600 years, Beijing's vast Forbidden City

has suffered from a recurring threat -

fire.

Caused by accidents...

or lightning strikes.

The Grand Wooden Hall of Supreme Harmony

has burned down numerous times.

It's actually been rebuilt seven times,

and each time it gets rebuilt,

it gets rebuilt with the technology of the day.

Rebuilding and restoring the Forbidden City

remains an ongoing task.

Today, work is being carried out on the gates, courtyards,

walls and ceilings.

In the Gate of Heavenly Purity,

many of the precious golden tiles have lost their shine.

Da Bing is a master craftsman from the Department of Restoration Skills

at the Forbidden City.

The Forbidden City has thousands of these gold leaf tiles.

But the gold has faded or eroded.

Restoration is a delicate process.

Each tile takes two weeks.

A piece of paper and black chalk is used

to copy the intricate tile pattern.

It's essential the design is exactly the same as the original.

This five-clawed dragon signifies the Emperor,

reserved only for him.

Once the tile has been copied and painted,

it is ready to be brushed with the precious gold leaf.

Pure gold is melted and mixed with bronze that adds a red sheen.

The alloy is still 98% pure gold.

Today, machines press it...

and press it.

In Ming times, workers would hammer it

until it was as thin as 1/500 the diameter of a hair.

It is cut up and carefully placed between sheets of bamboo paper.

The Forbidden City's restoration needs over 10 million pieces.

After days of work,

the master craftsman is ready to apply the gold leaf.

Finally, it's impressive enough for the Emperor himself.

The restoration work is still unveiling new surprises.

Hidden beneath centuries of dust,

researchers have uncovered rare evidence

of the original Ming decorations

in the Hall of Mental Cultivation's loft.

Over 500 years old, this is an extremely unusual find.

It is classic Ming Dynasty artwork,

with unique flower blooms, petals

and an exquisite attention to detail.

From the gorgeous paintwork and brilliant gold leaf,

to the giant wooden columns and monumental marble staircases,

the Forbidden City was the ultimate expression

of Yongle's ambition and power.

But his enjoyment of his pleasure palace was short lived.

In 1424, just four years after its completion,

the Emperor died

whilst on campaign.

In his last years, he still was

determined, against the opposition of his officials,

to go out and fight the wars.

And he was brought here to be buried

in great pomp and circumstance.

Yongle was laid to rest at this tranquil mountainside near Beijing.

This magnificent hall remains as he built it.

It stands as a symbol of Ming architectural genius

and a 22-year reign in which he changed China...

for ever.

The legacy of Yongle, on the one hand, is the physical legacy,

the great Forbidden City that we see today,

but on the other hand, it was his establishment

of the foundations of the Empire

that has survived down to this day.

For nearly 500 years after Yongle's death,

just 23 other Emperors ruled China from the Forbidden City...

..until the last Emperor, the boy Puyi,

abdicated in 1912 during a nationalist revolution.

He ended his days tending the palace gardens.

In 1925, a palace once forbidden to all,

opened its doors to the public.

The epic edifice had devoured goods

from the vast Ming empire and beyond...

..had demanded extraordinary logistics on land...

..water...

..and ice.

Had cost countless lives, but became medieval China's greatest creation.

Subtitles by Ericsson