All language subtitles for Samurai.Castle.2017.1080p.WebRip.H264.AC3.DD2.0.Will1869

(gentle music)

Kumamoto Castle

is known as one of Japan's three great castles.

It stood for 400 years,

capturing the people's hearts with its majestic beauty.

(gentle music)

(rumbling)

However, it was rocked by two violent tremors

during the magnitude 7.0 Kumamoto earth quake.

(gentle music)

The stone wall supporting the castle

collapsed in numerous places.

Kumamoto Castle suffered the worst level of damage

in its cultural properties

for the first time in years after World War II.

How shall the castle be restored?

(propeller whirring)

Using a drone equipped with a high resolution 4k camera,

NHK sent out to survey the damage.

The image then underwent over 3,000 hours of analysis

using the latest technology.

The result was used to reproduced

a virtual castle.

That led to unexpected discovery.

While many of the section of the stone walls

were built after the Meiji Era sustained damaged,

90% of the original stone walls withstood the earthquake.

Why were the older stone walls

more resistant to tremors?

What became apart from their construction method

was a mathematical formula

that even astounded today's scholars.

When construction originally began in Kumamoto Castle,

towards the end of the 16th century,

Japan was experiencing frequent major earthquakes.

The samurai ancestors

devised many technological innovations

to prepare for natural disasters.

Kumamoto Castle is finally revealing

its 400-year-old secrets.

How was the sturdy castle constructed?

And how should a castle full of samurai wisdom

be brought back to life?

The challenge to restore Kumamoto Castle begins.

(dramatic music)

The Kumamoto earthquake was a series of earthquakes,

including two jolts that recorded a maximum seven

on Japan's seismic intensity scale.

It took the lives of over 200 people

and forced more than 100,000 people to evacuate.

The castle complex is situated

on an extensive 242-acre campus.

How much damage did the earthquakes cost?

NHK, the Japanese public broadcaster,

cooperated with Kumamoto City

who is the administrator of the castle

in surveying the damage.

The stone walls that support the structure

had collapsed in many places.

Because of the dangerous conditions,

it was impossible to complete the survey of the damage

from the ground.

(propeller whirring)

So a drown equipped with a high-resolution 4k camera

was used to capture images of the damage.

This allowed the team to survey even the smallest damage

in places where it was too dangerous to approach.

(upbeat music)

Based on the GPS data,

the collective image were digitized.

The analysis of the entire dataset

took more than 3,000 hours.

The result was used to reproduce

a high-precision virtual castle in 3D.

The model could be studied from various angles

to reveal even minor details.

The extent of the damage became apparent for the first time.

The main tower made of two keeps

is the castle's central structure.

The tiles had fallen off

and weeds are growing on the roof.

The stone wall had collapsed,

blocking the entrance.

(gentle music)

The Higashi Jyuhachi-ken Turret,

listed as one of Japan's most important cultural property

was destroyed.

The building had collapsed

along with the stone wall.

It was a large scale collapse,

displaying 15,000 cubic meters in volume,

an equivalent of 7,000 metal barrels.

All 13 important cultural assets within the castle complex

were damaged.

The stone walls collapsed in more than 50 places,

dislodging more than 20,000 pieces of stone.

The five-story Lidamaru Turret

is situated south of the main tower.

Most of the stone wall under the turret had collapsed.

The 10-ton structure

was barely being supported by one narrow stack of stones.

The building floor was sinking form its own weight.

When measured by a computer,

the warp in the floor was 55 centimeters.

The entire building was in imminent danger of collapse.

Yet, matters were getting even worse.

There were many aftershocks.

They amounted to more than 3,500 in a month.

The situation remained critical.

An emergency operation

to limit further damage to the building began.

Would this intervention

prevent the structure from collapsing from the aftershocks?

A giant steel support arm

was carefully moved toward the turret.

The tip of the arm will be slid carefully under the building

so that the scaffold would cradle

and support the weight of the turret.

The work continued, adjusting the position of the arm,

several milimeters at a time.

They're now ready to insert the giant arm

where the stone wall had collapsed.

(gentle music)

One week after the operation had begun,

the arm that supports the weight of the turret was set.

That allowed access beneath the turret.

Though the aftershocks continued,

the spread of damage had been halted for the time being.

Toshihiro Tsumagari works for the municipality

of Kumamoto City.

He is the project leader for the reconstruction.

Kumamoto City proclaimed their goal

to rebuild the main tower,

the castle's symbol, in less than three years.

It was because the main tower holds a special place

in the hearts of the Kumamoto citizens.

There's a reason why the main tower

hold such a special place in the hearts

of the Kumamoto citizens.

(gentle music)

Kiyomasa Kato was the first lord of Kumamoto Castle.

He built the main tower 400 years ago.

(explosion booms)
(guns firing)

But the Seinan War or the Satsuma Rebellion

broke out during the Meiji Era.

The main tower was burned to the ground.

For more than half a century,

Kumamoto Castle was without a main tower.

In the Showa Era,

Kumamoto came under attack during World War II.

(explosions booming)

Many people lost their lives in air raids.

(gentle music)

Then in 1959,

plans were announced to restore the main tower

as a symbol of post-war reconstruction efforts.

Donations from citizens poured in,

and the reconstruction began.

The blue prints from that reconstruction had been preserved.

In the rebuilding efforts,

many Kumamoto citizens participated.

This is Yoshio Miyazaki.

(speaking in Japanese)

His late mother worked on the castle.

His mother, Suwaku, worked at the local lumber mill.

She volunteered when she heard

the main tower was being rebuilt.

She was put in charge of transporting roof tiles

and other construction materials.

Kumamoto Castle was brought back to life

in an effort to heal the scars of war.

The castle stands as a symbol

of the dedication and perseverance

of the citizens of Kumamoto themselves.

The city of Kumamoto announced their goal

to restore the main tower

before the third anniversary of the earthquake.

Six months after the quake,

the mayor inspected the main tower.

There was no major damage to the parts of the structure

built with reinforced concrete.

But the stone wall supporting the tower had collapsed,

and the stones had slid into the building.

Here is the entranceway

where many visitors used to come and go every day.

A technical proposal created by a construction company

to rebuild the main tower was submitted to Kumamoto City.

It was a proposal to rebuild the castle

with the elaborate earthquake resistant reinforcements.

First, a portion of the stone wall

would be dismantled and removed.

Next, the pilings and other structural supports

would be made more earthquake resistant.

After that, the stone walls would be rebuilt.

However,

Tetsuo Tanaka of the

Himeji Center for Research into Castles in Fortifications

complained that deliberately damaging

architectural artifacts, even temporarily,

was out of the question.

Another colleague, Hiroshi Kitano,

of Tohoku University of Arts and Design,

was also very critical of the proposed plan.

How could the mayor preserve the work

of cultural properties,

yet make the structures quake resistant?

Kumamoto City had to reconcile these two opposing interest

before they could start reconstruction on the castle.

In the mean time, NHK continued its investigation

into the damage to Kumamoto Castle.

Analysis of the three dimensional model

revealed something quite unexpected.

Uto Turret

was built during the castle's original construction.

(gentle music)

Although it was one of the oldest castle structures,

it withstood the earthquake.

Amazingly, the wooden structure

that had stood for 400 years

suffered no major damages.

The pillars and beams remained as they were

when they were first built.

The secret lay in the stone walls

that form the foundation of the structure.

When compared to the pre-quake survey data,

there was almost no deformation.

The stability of the stone wall

minimized the damage to the turret.

The neo stone wall is also one of the oldest structures

that have survived to this day.

It, too, has minimal deformation.

Was it just a coincidence that the original stone walls

withstood the force of the earthquake?

To solve this mystery, we looked into the history

of the stone walls.

During the 400 years since its construction,

Kumamoto Castle has gone through

numerous additions and restorations.

When the locations of the collapsed

from the present earthquake are mapped,

we see that 31% of the damage

occurred on stone walls restored in the post-Meiji Era.

Meanwhile, damaged to the walls

of the castle's initial construction

was limited to 10%.

90% of the samurai stone walls withstood the quake.

Kumamoto castle was built by Kiyomasa Kato.

He is known as a master castle builder

who was involved in the construction of many castles.

Why were the stone walls from the original construction,

the ones that Kiyomasa built, so sturdy?

To learn the secret,

we've asked experts to examine the 3D model.

Tomio Tamano is an expert on stone wall structures.

He believes the secret of why the stone walls

are resistant to earthquakes

lies in the way the stones were stacked.

Tamano focused on the angle of the stone.

Prior to the construction of Kumamoto Castle,

stones were stacked parallel to the ground

in most Japanese castles.

But in Kumamoto Castle,

stones are stacked at a 90 degree angle to the slope.

Stones stacked parallel to the ground

have a tendency to break loose

when sideways forces are exerted by an earthquake.

On the other hand,

When the stones are stacked at right angles to the slope,

the force is dispersed,

making it harder for them to dislodge.

(speaking in Japanese)

Another expert focused on the entire construction

of the stone wall.

Soichiro Kitagaki has been studying Japanese castles

for over 50 years.

Nori-gaeshi is the name given to the steep curve incline.

The intact neo stone wall is one example of this.

It's called musha-gaeshi

or samurai proof.

Musha-gaeshi is said to have been invented

by Kiyomasa Kato.

It is so named because it looks as tough it can repel

invading enemies

who are about to attack the castle.

It's the symbol of the impregnable castle.

Using simulation, we test a linear gradient

without musha-gaeshi.

The deduced forced applied to the stones by the tremor

is indicated by the arrows.

We see there's a large outward thrusting force

on the stones.

Now, the musha-gaeshi wall.

The force works along the surface of the stone wall.

The result clearly shows

that it's harder for the stone to break loose,

making it more resistant to earthquakes.

But while the original stone walls

mostly withstood the force of the earthquake today,

why was there so much damage to the stone walls

that were restored in the post-Meiji Era.

The researchers believed that the steep linear gradient

is one of the main factors.

Here is one example.

Hohoate Gomon Gate

was restored in the Meiji Era.

It suffered catastrophic damage from the earthquake.

The gradient of the wall they restored

was straight and almost perpendicular,

which we can see in the photo

shot before the 2016 Kumamoto earthquake.

The experts don't know

why they didn't use the musha-gaeshi curve.

The difference in the way the stones were stacked

changed the fate of the building hit by the earthquake.

During the course of the research,

the crew learned of the existence of an old book

with building instruction from musha-gaeshi.

The Secret Book of Stone Walls,

Ishigaki Hiden No Sho in Japanese.

It is said that the book was written

by Kiyomasa's stone wall building artisans.

First, to calculate the nori curve.

When calculating a 50% nori, multiply six by five

to get a three shaku nori.

Nori,

this unfamiliar word is repeated often in the document.

What does it mean.

Kitagaki was able to decipher the secret document.

First, he divided the stone wall into one ken,

or 1.8 meter sections.

Then he drew a small triangle.

Nori refers to the slope of this triangle.

The nori slant is determined by the length

of the base of the triangle.

By shortening the base

using the same formula as you go up the stone wall,

the nori wall curves back on its self.

It requires a very complex modern mathematical formula

to come up with this gradient.

It is now clear that the stone walls

were constructed to exact specifications.

400 years ago, samurai warriors

were living in a tumultuous age

of Japan's civil war.

They lived in constant danger of enemy attacks.

(weapons clanking)

Was musha-gaeshi invented to repel the enemies?

Could it be the Kiyomasa invented the structure

as an anti-quake measure?

Coming up, we'll unfold these mysteries.

(speaks in Japanese)

We'll also revisit the reconstruction efforts

at the castle today.

How will they make the castle more quake resistant

while preserving its value as a cultural property?

We'll be on-hand to witness the unprecedented challenge.

One expert has taken up the challenge

to solve the mystery surrounding the invention

of musha-gaeshi.

He is Soichiro Kitagaki.

Kitagaki headed for another castle created by Kiyomasa

to investigate.

The ruins of Ulsan Castle are situated on a mountain top

near Ulsan City in the southern part of South Korea.

(melodious piano music)

The curved incline was not utilized in Ulsan Castle

which was built by Kato Kiyomasa in 1593.

He built Kumamoto Castle six years after Ulsan castle.

So, the earthquake resistant curve

must have been invented in the interim.

What happened in the six years

between the two castle constructions

was the Keicho-Fushimi earthquake.

A huge earthquake swayed and damaged

every part of Fushimi Castle.

Fushimi castle suffered catastrophic damage

from the earthquake.

In this castle, Kiyomasa experienced a massive quake

that is said to have killed more than 1,000 kiyodowite.

In the aftermath, it is thought

he devised the anti-quake measure.

(speaking in Japanese)

Experts confirmed that at least 17 sections

of the Kumamoto Castle stone walls

matched the complex mathematical formula

deciphered from the Secret Book of Stone Walls.

Besides the musha-gaeshi curve,

there was another new method employed

in the stone walls of Kumamoto Castle

to make them even more quake resistant.

It was the well engineered angle

in which the stones were stacked.

Prior to building Kumamoto,

stones were stacked parallel to the ground

when building most castles.

But in Kumamoto Castle,

stones are stacked in a 90-degree angle to the slope.

This is what made the walls more quake resistant.

The experts investigated the changes

in the stacking angle.

This is the data of various castles around Japan.

Before the Keicho-Fushimi earthquake,

the stone walls were arranged parallel to the ground.

But after the Keicho-Fushimi earthquake,

the stones in Kumamoto castle were the first to be stacked

almost perpendicular to the slope,

raising the level of quake resistance remarkably,

and there after.

This technology was adapted in castles all around Japan.

(gentle music)

Kumamoto castle marked the evolution

of the castle construction technology in Japan.

To build the Kumamoto stone walls,

Kiyomasa called upon the artisans

who had experienced the Keicho-Fushimi earthquake.

By trial and error,

they attempted to build a sturdier stone wall.

(speaking in Japanese)

Work towards restoration has begun at the castle.

The collapsed stones were being carried away

by stone workers.

The work progresses with utmost care,

so as not to damage the stones.

These stones will be used to rebuild the stone walls.

They're all numbered and will be carefully stored.

(gentle music)

The stones amounted to more than 20,000.

Since no blue prints of the stone walls exist,

how will the team rebuild the walls?

NHK decided to team up with a researcher

to create a new software to facilitate restoration.

It's programmed to instantly show

the most likely place where a stone may have been positioned

in a stone wall.

(suspenseful music)

When you trace the outline of a stone's flat surface,

the program recognizes and computes the shape.

The screen shows where the stone

is most likely to have been located

before the earthquake.

This method of determining the location

of each of the 20,000 stones is continuing.

As the reconstruction of Kumamoto Castle began,

a new risk factor came to light.

Even in the stone walls that escaped damage,

bulging parts were found.

The entire center section of this stone wall

was also bulging.

Three weeks after this bulge was discovered,

it suddenly collapsed.

The damage is spreading unseen

through the internal structure.

Tatsauki Nishigata who study stone walls structures

has been investigating the bulges.

This is Nishigata's analysis

of why the stone walls have bulged.

The inside of the stone wall

is stuffed with cobblestones.

Previously, they were thought to absorb

the sway of the quake

and stabilized the stone wall.

But the two major Kumamoto tremors

have been followed by countless aftershocks

for an extended period of time,

increasing in recent years.

These frequent tremors

have caused the cobble stones to sink,

forcing the wall stones outward.

When the outward force becomes too great,

the wall collapses.

(rumbling)

As the investigation progressed,

the original stone walls

thought to be more resistant to earthquakes

were also to discovered to have some bulges.

In the entire castle complex,

no less than nine sections have been found to have bulges,

and two of them were in imminent danger of collapse.

Analysis was conducted on one of the two sections.

The concentration of red

indicates a high probability of collapse.

If even a portion of the wall collapses,

it could cause a chain reaction

that may lead to large scale failure.

What if the damage gets even worse?

For the Kumamoto citizens who have devoted their energies

to speedy reconstruction,

this is extremely alarming.

If the proposed reinforcement works are applied

by using cutting-edge technology,

the stone walls will be more quake resistant,

but that can take away from its worth

as an important culture property.

The mayor was once again faced

with a difficult dilemma,

how to preserve the historical value of the castle,

yet strengthen it to withstand earthquakes.

Kumamoto Castle experienced two great quakes

after Kiyomasa's death.

They took place in 1619 and 1625.

A stone wall that was restored during those earthquakes

has survived to this day.

The restored wall is known for its musha-gaeshi curves.

The right curve is attributed to Kiyomasa

and the left is the extension Tadatoshi built.

Builders at the time placed large stones

at the curved corner of the wall.

This was to make Kiyomasa's musha-gaeshi wall even sturdier.

By using larger stones,

the contact surface areas increased,

making the structure more stable.

Mayor Onishi has been trying to cope

with the conflicting demands

in preserving the value of the cultural property

and the need to make the structures more quake resistant.

As the further risks of earthquake damage loomed,

the cultural experts also started to feel

that there is a need to make the wall

more resistant to earthquakes.

Specifically, concerning stone wall reconstruction,

the experts proposed incorporating

some of the old technology chronicled

in the Secret Book of Stone Walls.

As to the bulges in the stone walls,

they debated the use of modern measures,

such as special sheets

to prevent the cobble stones from sinking.

Finally, the construction to rebuild the castle

began in a full scale.

(birds chirping)

A year after the Kumamoto earthquake,

the castle grounds that have been off limits

was partially open to the public.

(gentle music)

With the wisdom of their samurai predecessors,

the major and experts perceived

with the most important issue in mind,

the protection and preservation of human life.

Restoration of Kumamoto Castle

will continue for years to come.

(gentle music)