All language subtitles for Ancient.Engineering.S01E04.Rise.Of.The.Super.Castle.1080p.AMZN.WEB-DL.DDP2.0.H.264-NPMS_track3_[eng]

- [Narrator] We are surrounded

by extraordinary
feats of engineering,

constantly pushing the
boundaries of what's possible.

- Without engineering,
there'd be no modern world.

- [Narrator] Gigantic cities,
amazing infrastructure,

and ingenious inventions.

- Engineering is the key to
turn dreams into reality.

- [Narrator] To reach
these dizzying heights,

today's technology

relies on breakthroughs
made by ancient engineers.

- It's mind boggling
how they did this.

- [Narrator] How did
early civilizations

build on such a scale?

- They raised the
bar for construction

in a way that no one
thought possible.

- The sheer engineering ability

that is, in itself, impressive.

- [Narrator] By defying
the known laws of physics

and daring to dream big,

they constructed
wonders of the world,

from gigantic pyramids
to awe inspiring temples

and mighty fortresses,

all with the simplest of tools.

- Cannot imagine the skills
people would have needed

to build like this.

- [Narrator] Now it's possible
to unearth the secrets

of the first engineers.

- They managed to
construct edifices

that have survived
the ravages of time.

- [Narrator] And
reveal how their genius

laid the foundations for
everything we build today.

[dramatic music]

In the modern world,
military power is vital.

- You're thinking about how
you want to attack your enemy

or how people will
be attacking you.

- [Narrator] Nations arm
themselves to the teeth

with guns, rockets, aircraft,
the list is endless.

- Groundbreaking new technology

that gives one side or
other, the advantage.

- [Narrator] Globally,

defense costs around
$2,000,000,000,000 a year.

- We want to be secure.

- [Narrator] And key to
all military strategy,

impregnable defensive structures

to protect systems and
personnel from attack.

- Troops need somewhere to
rest, to recuperate, to train.

- [Narrator] Bases
built with solid walls,

carved into mountains,
bunkered deep underground,

or constructed beneath the ice.

But these modern defenses
wouldn't have been possible

without ancient
engineering breakthroughs,

leading to the most iconic
defensive structure of all time,

this is the history
of the castle.

[atmospheric music]

[whooshing sounds]

[atmospheric music]

During the Middle Ages,

Europe witnessed the astonishing
evolution of the castle

and two countries

would see the greatest
concentration of
these structures

anywhere in the world.

- There were castles built all
across Europe in this period,

but what's happening in England

and what's happening in Wales

provides us with a
wonderful set of insights

into the way in which
the castle evolves.

- [Narrator] The conquest of
wild and inaccessible Wales

came at a time

when castles were an
essential feature of warfare.

The Normans, invading from
France, had overwhelmed England

with the help of a network of
castles across the country.

- The castle was
a pivotal weapon

in the Norman occupation
of the 11th century.

- [Narrator] But to take control
of this hostile territory,

totally new castle
technology was required.

And their efforts would
climax spectacularly here,

at Caerphilly
Castle, South Wales.

- Caerphilly is an absolute
masterpiece of castle design.

- [Narrator] This vast and
impregnable military bastion

was the last word in
medieval engineering,

a daunting prospect for
any would-be attacker.

- Caerphilly stands
out as a castle design

because centuries
of improvement,

centuries of innovation
are all brought together

in one coherent whole.

What's particularly noticeable

is the use of water
to defend the walls,

but it's also a
concentric castle design,

it really is a magnificent
engineering achievement.

- Here we're talking
about 30 acres of castle,

multiple walls,
multiple moats, lakes,

this is castle building
on a grand scale.

- [Narrator] Perhaps the
greatest castle on earth,

Caerphilly was the
first super castle.

Caerphilly lies at the
edge of the Rhymney Valley

in South Wales,

and is the largest
castle in the country.

- It's built at lightning speed,

a workforce of hundreds
running into thousands

and it's not just
stonework at Caerphilly,

there's real civil
engineering going on.

- [Narrator] Vast and
sophisticated water defenses,

an ingenious and impregnable
system of concentric walls,

creating impassable
killing zones.

- It's an example

of the way in which the
castle design evolves

to take account of
particular weaknesses

that had been identified
in castles before.

- [Narrator] Grand
circular turrets,

watchtowers that proved
impossible to undermine,

and enough space
and water supplies

to withstand the longest siege.

Caerphilly and other 13th
century super castles

were so brilliantly engineered

that any attack would
likely prove futile.

But how did medieval
builders and architects

manage to create such
extraordinary structures?

The last of the
great super castles

were built more
than 500 years ago,

but these mighty
medieval fortresses

and the construction
techniques they pioneered

have influenced
defensive engineering

up to the present day.

[atmospheric music]

Although modern armies
no longer build castles,

they still need strong,
secure buildings

to protect people, valuable
objects, and political systems,

nowhere more so than
in the high tech world

of national security.

- We still want to be
secure in our buildings

and make sure that we protect
what's inside the building,

so, in a way, we're using
similar security principles

from medieval castles.

- [Narrator] Today,

one of the most secure
military bases in the world

is the Cheyenne Mountain
Complex in Colorado Springs.

Indebted to the
ideas and engineering

of the great castle
builders of the Middle Ages

and just like Caerphilly, it's
famed for being impregnable.

- It's been designed to
withstand any type of threat,

even electromagnetic
pulse or nuclear attack.

- [Narrator] This giant bunker

was built under 2000
feet of solid granite,

tough enough to withstand
a nuclear, biological,

or electromagnetic attack.

The influence of medieval
castle builders is everywhere

in Cheyenne,

beginning at the front door.

- Medieval engineers
understood that the gate house

was the crucial
point for security

and we see this reflected
in the design of Cheyenne,

with its two giant blast doors.

- [Narrator] Each is made
of concrete and steel

three and a half feet thick,
weighing over 20 tons.

Cheyenne's effectiveness

rests on being engineered
for maximum strength

and the story of
the medieval castle

was driven by the same impetus.

But where did the ideas

behind these ultimate
fortresses originate?

[whooshing sounds]

Throughout the ancient world,

early civilizations
built defenses

to protect towns,
cities, and territory.

Ancient literature, from
the Bible to the Trojan War,

gives vivid accounts
of cities under siege.

And, in the Classical Era,

the Romans became masters
of the construction

of fortified settlements,

as their empire spread across
Europe, Africa, and Asia.

Rome built a network
of forts and walls

to separate the empire
from its enemies.

One of the best known
is Hadrian's Wall

in northern Britain,
stretching over 70 miles.

- When the Romans
invaded in 43AD,

they moved steadily
across Britain,

gathering territory, building
roads, building fortresses.

- [Narrator] Behind
Hadrian's Wall were forts,

evenly spaced a half
day's march apart,

so each could respond quickly
if another was attacked.

Early forts were
built from timber,

replaced by stone as they
became more established.

But midway through the first
century, Rome was under attack,

so the Romans abandoned Britain

to take care of
matters back home.

Britain wouldn't see defenses
built on this scale again

for centuries to come,

when a new invading force

put up its own
defensive structures.

Clues to their nature can
be found on an artwork

depicting one of the most
famous battles in history.

[men shouting]

William the Conqueror's
invasion of England in 1066

would forever change the
country's landscape and destiny.

To establish regional power
bases throughout the land,

the Normans built something

never seen before on
these shores, castles.

- The castle was, arguably,

the key innovation that the
Normans bring to England,

castles were scarcely
known in England

and, for this
reason, the English,

in spite of their
love of fighting,

could only put up a
weak show of resistance

to their enemies.

- [Narrator] Wherever
William marched his army,

he built a new castle,

in a style known as
motte-and-bailey.

- It's a move from what would
be seen as kind of a fort,

to what we would understand

as something very
obviously a castle.

- They were built in places

that were strategically
important or visually important

so that these new castles,

these new symbols of
dominion and subjugation,

could be seen for miles around,

so that it was very clear that
there was a new lord in town.

- [Narrator] It is believed

that as many as 1000
motte-and-bailey castles

were built throughout
Britain by the Normans,

but none have survived intact.

So how can their construction
secrets be understood?

Luckily, the Normans
left behind a blueprint

showing how it was done.

The evidence is woven into a
unique historical document.

In a museum in the French
city of Bayeux, in Normandy,

hangs the world famous
Bayeux Tapestry.

It depicts

events leading up to the
conquest of England in 1066.

- The Bayeux Tapestry,
it's absolute gold dust

because it gives you
an artist's impression

of what these early
castles look like.

- [Narrator] The tapestry
reveals that early castles

were nothing like the mighty
edifices of later years.

- It's clear from
the Bayeux Tapestry

that they're being,
first and foremost,

fashioned in wood and
constructed out of wood.

- [Narrator] The motte element

was a large mound
of piled up earth,

at the top, a wooden
tower was constructed.

- To build a motte you are
shifting a lot of earth,

perhaps 20 or 30,000
tons of earth,

so it's backbreaking work
for hundreds of people.

- One of the key advantages of
having the motte, of course,

was it gave you height,

it also made it very, very
difficult to attack on horseback

or even on foot because you'd
have to clamber up that slope.

- [Narrator] Below the
motte, the bailey was built.

- [William] The bailey was the
economic heart of the castle,

this is where the forges were,

the merchants
traded, the houses,

but the lord lived in
his defensive castle

up at the top of the motte.

- [Narrator] There
are several reasons

why none of these early castles

survive in their original form.

One is a fatal flaw
in their design

that attackers could
all too easily exploit.

Throughout the world,

there is one destructive element

that when it takes hold,
leaves a trail of devastation.

From wildfires in
California and Australia,

to skyscrapers collapsing

as they're turned
into burnt out shells,

fire can quickly become
humanity's worst enemy.

- Fire is always a risk,

whether accidentally
started from within

or whether you have fire
brandishing attackers without.

- [Narrator] The original
motte-and-bailey castles

were constructed with
wooden palisades,

wooden houses, wooden keeps,

so they could easily
be ignited by bonfires

lit against their outer wooden
fences, hurling torches,

or by archers
shooting fire arrows.

When fire took hold, those
inside were forced to flee,

allowing the attackers
to take them prisoner

or to slaughter them.

The use of fire as a weapon

has continued right
up to modern times.

During the Second World War,

incendiary bombs were
dropped on enemy targets,

designed to start large scale
firestorms on the ground.

Incendiary bombs
contained thermite,

a mixture of aluminum
powder and iron oxide

that burns at a very
high temperature.

- They were encased in
an element like magnesium

which, itself, is
highly flammable

and they might have
also contained materials

like oil or pitch,

which would quickly set
fire and spread the fire.

- [Narrator] The
German Luftwaffe

dropped these weapons on
London during the Blitz

and allied air forces used
them to create firestorms

in Dresden and Tokyo.

- Incendiary bombs can destroy
vast areas of territory,

they can change the face
of cities in seconds

with really sudden
dramatic impact,

if thousands of them are
dropped, there's nowhere to run,

there's nowhere to hide.

- [Narrator] Fire could have
the same devastating impact

on a medieval wooden castle.

So engineers needed
to develop structures

that would be stronger,
longer lasting,

and, most importantly,
fireproof.

The answer, improved technology
and a new building material,

stone.

The first examples were built
as much as a display of power

as for military purposes.

- The Normans began to
build castles in stone

as a powerful symbol that
they were here to stay,

that their invasion
was permanent.

- [Narrator] They would have to

be jaw-droppingly impressive,

seemingly invincible,
and built to last.

William the Conqueror
laid down the template

with one of the mightiest
castles ever built.

Infamous as a
terrifying Tudor prison

and renowned as the home
of the crown jewels,

the Tower of London.

The White Tower

is the most recognizable
castle keep in the world.

- At the time,

nothing of this scale
had been built in Britain

since the Romans.

- William's white tower in
London was completely different

because it was made of stone

that was imported from Normandy

and he built it in that
part of the River Thames

to dominate the
people of London,

to say, I am your new king.

- If you're sailing
up the Thames,

coming to London for the
first time, bang, there it is,

just to say, I'm in
charge, I am all powerful.

- [Narrator] The tower
was a high security base

for the royal family and
their military entourage.

- The White Tower had
a very key feature

and that is that the entrance
was on the first story,

so you couldn't get
in at ground level,

it was built with immense walls,

it was completely impregnable.

- [Narrator] Unlike a
typical royal palace complex

spread across a
number of buildings,

here, for security reasons,

the meeting hall,
chapel, and bedrooms

are all stacked on top of one
another in a high rise design.

William was never to see
the tower in its full glory,

it wasn't completed until
1100, 13 years after his death.

But his fortress would
play a central role

in British history,

a place notorious for
murder and mystery.

Two of Henry VIII's wives
were executed at the tower

and Guy Fawkes was
imprisoned here

following his attempt
to blow up parliament.

Richard III reputedly had his
two young nephews murdered

and their bodies
hidden behind a wall.

And in 1861, a thief tried
to steal the crown jewels.

For centuries,

the tower has stood on
the banks of the Thames

as a potent symbol.

Today, the super
rich and the powerful

continue to use tall or
grand buildings to impress.

Built to honor the Kim dynasty,

North Korea's Rungrado Stadium
is the largest on earth.

For centuries, countries have
competed for the prestige

of having the tallest
building in the world.

Upon completion in 2010,

the Burj Khalifa
seized the crown

for the United Arab Emirates,

standing a whopping
2,716.5 feet high.

And there are those with a
few billion dollars to spare

who choose to build
their own towers.

[whooshing sounds]

[soft music]

Back in medieval England,

William the
Conqueror's stone tower

was the first of its kind.

But, subsequently, a
vast building project

would take the
concept of the castle

and castle engineering
to a whole new level.

Rochester Castle stands on
the banks of the River Medway

in the English county of Kent.

It was designed with some
radical engineering innovations

to be ready for any attack,
foreign or domestic.

Traces of damage
inflicted by enemies

are still visible on the
fabric of the castle today

but they weren't left
by invading forces,

rather, a homegrown assault.

- The design of
Rochester is unique

for two very important reasons.

The first is that it's the
first tower in the country

to be built on four stories,

so it's much taller

than any other tower
that's been built

and secondly, is the
construction of a forecastle.

- [Narrator] The forecastle

is designed to protect
a castle's entranceway.

- In any fortification,

the weak point is always
gonna be the entrance.

- [Narrator] At Rochester,

a large stone extension
houses a giant waiting room

and, crucially, conceals
the main gate from attack.

Any assault would now
involve an extended approach

that could only be made on foot,

an attacking force would
be helplessly exposed.

- The way it is engineered

is specifically to defend with
the fewest number of people

against the maximum
numbers of attackers.

[keypad beeping]

- [Narrator] Entrance security
is still evolving today,

there are countless
ways to keep a door shut

and the world's most famous
vault is at Fort Knox.

Fort Knox in Kentucky

is home to the United
States Bullion Depository,

it stores the country's
precious metal reserves

including over
4,000 tons of gold.

- The expression, it's like
trying to get into Fort Knox,

implies a really high
level of security

and certainly, in the
case of Fort Knox,

what we're talking about

is somewhere that's nearly
impossible to access.

- [Narrator] Fort Knox
can only be entered

after negotiating four
perimeter fences, armed guards,

and a state-of-the-art
electronic security system.

The building itself is
seemingly impregnable,

it's made of concrete lined
granite and reinforced steel,

enabling it to withstand attack.

And, just in case,

digital technology
presents a final barrier.

- The security codes are shared

amongst a number of people

to make it really difficult
to access this building.

- [Narrator] So far, at least,

no one has ever come
close to breaking in.

[whooshing sounds]

For over 100 years,

Rochester Castle was
considered equally impregnable,

but in 1215, a group of rebels
attempted to seize control

of this key military stronghold.

At that time, it
presented a major threat

to the ruler of England, King
John, he ordered a siege.

- John is determined to break
into this gargantuan castle,

so he throws everything he
can at it for seven weeks.

- [Narrator] So
what kind of weapons

were at King John's disposal?

If you want to smash
your way into a building,

you might think the easiest
way is through the front door.

Giant battering rams had been
developed in ancient times,

the Assyrians had
sophisticated rams

as early as the
ninth century BC.

- Battering ram is quite an
interesting piece of technology,

the idea

is that when you put a large
force into a small area,

you get a very high
pressure out of it.

- [Narrator] In theory,
such intense pressure

would puncture the
toughest of barriers,

but the entrance
to Rochester Castle

was up on the first floor,

protected by the
forecastle, heavy doors,

and a portcullis,

making it impossible to
maneuver a large battering ram

anywhere near the gate.

So King John ordered the
deployment of a new weapon

to break the siege,

the trebuchet.

- The engineering principles
behind the trebuchet

are exactly the same as you
would imagine a catapult.

- [Narrator] A trebuchet

uses the energy of a
falling counterweight

to launch a projectile,

such as a large rock
contained in a sling

attached to a lever arm.

The counterweight is
hoisted into the air

and cocked with a pin,

once the pin is removed,

the counterweight
immediately drops

and the lever arm
sharply rotates,

throwing the rock hundreds
of feet through the air

towards its target.

[whooshing sound]

This high-tech medieval weapon

was engineered to
inflict maximum damage

and King John had
sent five of them

to the siege of
Rochester Castle.

- Those hiding inside castle
walls might've felt pretty safe

until their combatants
on the opposite side,

brought up their
heavy artillery.

- So he's hurling great
rocks, carved balls of stone

at the castle, trying
to smash his way in.

These five machines didn't
cease in their barrage,

day and night.

- [Narrator] Despite being
the most advanced weapons

of their day, the
king's trebuchets

failed to dent Rochester's
mighty stone walls

or the rebel's resolve,
the siege continued.

In the modern world,

the search for new weapons

is still a never ending
technological arms race.

Each new weapon is counteracted
by a new form of defense,

which, in turn, creates a demand

for more powerful
attacking technology.

Today, as ever deeper
and more ambitious

subterranean command
centers are constructed,

a new generation of weaponry

has been developed
to reach them.

- Known as bunker busters,

these are bombs which can
penetrate deep into the earth

or right through dozens of
feet of reinforced concrete

before exploding and causing
absolute devastation.

[dramatic music]

[whooshing sounds]

- [Narrator] At the 13th century
siege of Rochester Castle,

going underground was now
King John's only option.

His tactics would expose a
weakness in castle design

that even stone construction
couldn't address.

- The only way John
is, in the end,

able to get into that building

is to undermine it,

which is to say to dig a
tunnel under one corner.

- Then when the tunnel had
been dug right under the wall,

they would set
fire to that timber

and the wall would collapse.

- [Narrator] It caused a
good proportion of the keep

to come crashing to the ground.

- The way they use fire
to undermine structures

is by basically
destroying the foundation

that the structure is built upon

and once the foundation has gone

and you get a weak
point in the structure,

then the structure has
no substance to stand on.

- [Narrator] Amazingly,
even after the collapse

of the southeast
corner of the keep,

the rebels fought on.

- In the end, it's hunger
that does for them,

it's hunger that induces them

to eventually
surrender to King John.

- [Narrator] The
fall of Rochester

proved that the new
generation of stone castles

were not yet invulnerable,

medieval engineers
had their work cut out

if they were to defend
against tunnelers.

And tunneling has
remained a military tactic

right up to the 20th century.

Playing a role in some of the
bloodiest military campaigns

of the modern era,

during the Second World War,
Japanese soldiers used tunnels

on the Pacific
Island of Iwo Jima,

constructing miles
of hidden passageways

to defend against or
attack American forces.

Tunnels were also
used to great effect

during the Vietnam War
of the 1960s and '70s.

- Viet Cong built a
huge network of tunnels

about 20 feet below ground,

these tunnels would allow
soldiers to travel for miles

to conduct surveillance,
to set traps,

or to launch surprise attacks.

- [Narrator] After which,

they could disappear
underground to safety.

Tunneling is a tried and
tested dirty trick of war.

[whooshing sounds]

And the undermining
of Rochester Castle

proved a valuable lesson
to medieval engineers.

When they came to
rebuild the fortress,

they introduced a
radical new feature.

- The square tower at Rochester

was replaced by a round tower.

- Circular towers are
structurally stronger

than square towers,

they have less
points of weakness.

- [Narrator] When a projectile

hits the corner or
edge of a square tower,

it can easily bring it down

but if it hits a circular tower

it's more likely to be
harmlessly deflected.

Circular towers of various kinds

proved a game changing
advance for castle security

and the advantages
weren't only structural.

From a surveillance perspective,

round towers gave bowmen a
far wider field of vision,

eradicating
watchtower blind spots

created by the 90 degree
corners of square towers.

[dynamic music]

Today, the curved wall
is used by architects

to design and build

some of the most elaborate
and jaw-dropping buildings

in the world,

liberation from the
rectangular forms

that traditionally
dominated city scapes.

- The Absolute World
tower in Canada,

where you've got these
amazing curved towers

and the taller one is actually
nicknamed Marilyn Monroe

for its iconic hourglass figure.

- Guggenheim Bilbao is
one of the great buildings

of the late 20th century

and it's a building that
looks utterly impossible.

There's architects
wanting to explore,

not just the possibility of
building circular buildings,

but of completely
defying this square box

and building things that
look utterly unbuildable.

[whooshing sounds]

- [Narrator] By the time
Rochester got its round tower,

other elements of
castle engineering

were also improving,

with lessons learned far
from the battlefields

of England and Wales.

From its seventh century
emergence in the Middle East,

the Islamic faith
spread far and wide,

east towards India
into Northern Africa

and up into Southwest Europe.

By the 11th century,

knights from Europe were
embarking on crusades

to recover the Holy
land from Islamic rule.

Here, they'd build new
fortresses on a massive scale.

One of the most powerful
of these crusader castles

can still be found 25 miles west

of the city of Homs in Syria
near the Lebanese border,

Crac des Chevaliers.

- Crac des Chevaliers was unique

because it's one of
the earliest examples

of a concentric castle,

which means that the castle

sits within its
own curtain wall.

- [Narrator] Concentric castles

consisted of an
outer circuit wall

with built-in round towers

and an inner wall built
higher with additional towers.

- The idea is that
that inner wall

can protect and defend
the top of the outer wall,

and that these two walls
are broadly parallel.

- [Narrator] With the
concentric layout,

defenders could protect the
outer perimeter from attack

and then fall back, if need be,

into the center of the castle.

The wall within the wall at
Crac was highly influential

and not just in
the medieval world,

the concept has been
endlessly reused

to keep people out and
sometimes to keep people in,

right up to modern times.

[dramatic music]

[soft music]

During the Cold War

in the second half
of the 20th century,

control of Europe was divided
between NATO in the west

and the Warsaw Pact in the east.

Berlin in Germany

was initially shared
between the two blocks,

but in August, 1961,
in just two weeks,

east German forces

erected a makeshift barbed
wire and concrete block wall,

dividing one side of
the city from the other,

the Berlin Wall.

Over the following
months and years,

the wall was further reinforced.

- The Berlin Wall was actually
constructed of two walls

with an area in between

that was filled
with watchtowers,
anti-vehicle trenches,

guard dog runs,

in effect it was a killing zone,

much like we might say

the area between the concentric
walls of a medieval castle.

[whooshing sounds]

- [Narrator] The medieval
castle, Crac des Chevaliers,

also had some defensive
tricks up its sleeve.

- So, half the battle's won

when you're creating an
impregnable fortress,

if you stick it up on
a nice rocky outcrop.

- [Narrator] Over
2,000 feet high,

surrounded by steep inclines,

the landscape gave this
castle a defensive headstart.

Any approach

would leave an attacker
dangerously exposed.

- Crac des Chevaliers

also has a very
distinctive entranceway,

it's called a bent entrance

in which anyone
entering the castle

is essentially funneled
into a bottleneck,

making them very
vulnerable to attack.

- [Narrator] Although
it survived many
assaults and sieges,

the castle eventually
fell in 1271

and the last of its crusader
knights either surrendered

or were killed.

Despite Crac's ultimate defeat,

advantageous geography
can boost security,

used effectively, it will
deter most would-be attackers.

There are some astonishing
later examples,

including the Predjama
Castle in Slovenia

built in the mouth of a cave,

Mont-Saint-Michel

built on a tidal island
in Northern France,

and Trosky Castle in Bohemia

constructed on a hilltop
surrounded by forest.

Unsurprisingly, engineering
ideas from the Crusader wars

traveled back home with
the returning soldiers.

- It's almost like the Holy Land

becomes a laboratory
for castle design.

- [Narrator] In the
late 12th century,

the idea of building two
concentric defensive walls

arrived in Northern Europe.

Dover Castle is sometimes
called the key to England.

Built by Henry II,

it was the most expensive,

most heavily defended
fortress in the kingdom.

- Dover Castle was
an immense tower

protected by a very
distinctive curtain wall,

which had towers
all the way along it

and the key thing
about Dover Castle

was the heavily
defended entranceway.

- [Narrator] At the heart of
the castle was a giant keep,

with walls up to 20 foot thick.

Its outer wall incorporated
14 rectangular towers

set on projecting plinths,

as well as a tower
with firing platforms

and multiple narrow windows
for archers and crossbowmen.

It's believed that the crossbow

had only recently
arrived in England

with the Battle of Hastings,

though not a great weapon
on the battlefield,

it proved a game changer
for castle defense.

- Crossbows are probably
the most important weapon

in a siege situation,

because they are so deadly,

they are able to pick off
a well armed mounted knight

because of their range
and penetrative power.

- With the bow and arrow,

you are basically having
to use your strength

to pull the bow back,

but the crossbow had
this added feature

where you could
stand there waiting

until the optimal moment
to pull the trigger

and release the arrow.

- [Narrator] The
defense of Dover Castle

relied on surveillance and
the skill of crossbow snipers,

hidden behind narrow arrow slits

to attack any approaching enemy.

[atmospheric music]

Modern sniper weapons
are similarly engineered

for long range accuracy,

reducing the enemy's
combat ability

by neutralizing
high value targets.

- If you know about snipers,
you know about their accuracy,

the knowledge

that they might be positioned
in the war zone around you

would be paralyzing,

there's no sound,
there's no warning,

just suddenly the hit and
your comrade is killed.

- [Narrator] Sudden death was
something all too familiar

to those attacking castles,

but castle technology
continued to evolve.

In the final decades
of the 13th century,

a new battlefront opened up

when successive English kings

turned their attention
to the conquest of Wales.

It was an opportunity

to combine the accumulated
engineering ideas

of the last 150 years

to create the
ultimate super castle.

- So the great Welsh
castles of the 13th century

are a sort of zenith in
castle building design.

- Wales is famous for,

arguably, having more
castles per square mile

than any other part of Europe.

- [Narrator] During the
reign of King Henry III,

one of the most powerful and
ambitious barons in the land,

was Gilbert de Clare.

He was tasked with
preventing South Wales

falling into the hands
of the Welsh leader,

Llywelyn ap Gruffudd,

who controlled most of Wales.

De Clare decided

the key to military
domination of the region

would be the construction
of a giant castle,

it would be a completely
new kind of structure

and it would be built at the
mouth of the Rhymney Valley

in a town named Caerphilly.

Construction began in 1268,

so what was so special
about Gilbert's castle?

Right from the beginning,

Caerphilly changed the rules
of medieval engineering.

- [William] It's made
up of a series of walls

and gateways and towers,

and each of those
gateways has portcullises,

and each of them is
defensible in its own rights.

- [Narrator] It represented
a huge leap forward

in defensive capabilities.

- You've got the capacity

to sustain multiple
different attacks

and to ensure that the
castle never completely falls

into the hands of those
who are besieging it.

- [Narrator] So what
were the challenges

faced by potential attackers?

- The main castle
sits on an island

in the middle of a moat

and that moat is retained
by a north and south bank,

but it's to the east

where you have a fortified
dam with gate houses.

- [Narrator] Unlike
many castles,

Caerphilly's moat couldn't
easily be drained,

so tunneling under its
walls was impossible.

It may seem that moats
are a thing of the past,

but, in fact, they're a
defensive design classic

still in use today.

- The moat is such a
successful means of security

that even the US
Embassy in London,

with its state of
the art design,

incorporates a moat.

- [Narrator] The Embassy

is Central London's
first new moated building

since the Medieval Era.

Intended as a defense
against terror attack,

it's said to be eight feet deep

and wide enough to
swallow any truck bomb

charging towards the building.

So given its highly
effective moat system,

was there any way

an attacker could breach
Caerphilly's walls?

- With the sheer amount of
stonework you've got there,

the sheer size of it,

you've got walls within walls,

walls studded with
towers, seven gatehouses,

all of those things
on top of one another,

it comes very close to being
an impregnable fortress.

- I think only a madman

would want to take on
something like Caerphilly,

the whole point of
the construction

of Caerphilly, in
the first place,

is simply to say don't
even think about it.

- [Narrator] But
within a century

of Caerphilly's completion,

a new weapon arrived
on the battlefield,

its incredible destructive power

would signal the beginning of
the end for the super castle.

Throughout history,

the invention of new
ways to kill or destroy

has abruptly changed
the course of wars.

In May, 1945,

the Second World War
came to an end in Europe

with the surrender
of German forces.

However, in the Pacific,

the fight with Japan
was still raging,

but one of the deadliest
engineering breakthroughs

of all time, was
about to emerge.

Codenamed the Manhattan Project,

this was the top secret
American-led effort

to develop a functional
atomic weapon.

And in August, 1945,

the devastating power
of this new technology

was made apparent

when bombs were dropped
on Hiroshima and Nagasaki.

Within days, Japan surrendered.

[whooshing sounds]

The engineering development

that finally brought
the medieval super
castle down to earth

also turned out to be
something explosive.

- The arrival of the cannon

fundamentally changed
the role of the castle,

because those castle walls

could not be protected
from cannon fire.

- A cannon is very effective
because you've got more power

and you can direct the
payload more accurately,

so you can essentially
hit your target

with greater firepower and
cause more damage accurately.

- [Narrator] The cannon
consists of a strong metal tube

with a plug at one end,

a small hole for a fuse is
drilled through the barrel,

gunpowder is pushed
down into the tube,

then a solid ball is inserted

so that gunpowder and ball

are pressed against
the plugged end.

A fuse in the small
hole is then lit

to ignite the gunpowder.

The resulting explosion shoots
the ball out of the tube

at high speed
towards the target.

The damage is done

by the sheer power of
the blunt force impact.

To combat the cannon,

castle design changed, walls
were no longer built tall,

but thick and squat,

many were built of earth
reinforced with stone

to better absorb cannon shot.

Castles were no longer the
places of refuge and safety

they once had been.

- So from the 15th
century onwards,

castles begin to experience
a change in purpose

and a change in design,

and, partly, that's because
models of warfare change,

it becomes harder and harder
and harder to defend castles

against improved
forms of attack.

- [Narrator] Castles
gradually evolved

from vital military
defensive structures

to symbols of power,
pomp, and self-promotion.

Developments in engineering

now focused not so much
on improving defenses,

as improving the architecture,
accommodation, and comfort.

- So what one sees is an
evolution from the castle

into the manor house,
into the royal palace,

into things that we
much more obviously

associate with courtly life,
with aristocratic life.

- [Narrator] Grand old castles,

like the famous Prague Castle,

became centers of government
or royal residences,

such as Windsor.

Even today, the super rich
still enjoy building castles

with varying degrees of irony.

Sadly, war itself has not
been banished to the past,

defense of citizen's property
and nations remains vital

and now it's even
closer to home.

- War is no longer confined

to some sort of far
distant battlefields,

it's all around us all the time,

we're increasingly living in
an age of digital warfare.

- [Narrator] Battle lines
are now drawn in cyberspace

and the need for defense
remains every bit as important

as it was centuries ago.

- In this digital modern age,

our most valuable resource
is information and data.

- So the firewall
on your computer

acts rather like a curtain
wall around a medieval castle.

- And just like in
the medieval times,

people are constantly
trying to attack

and steal the valuable
resource behind that wall.

[soft music]

[atmospheric music]

- [Narrator] Castles were once

the most powerful military bases

in the Western world,

the products of breathtaking
feats of medieval engineering

dominating the
European landscape

throughout the Middle Ages.

New weapons were created
to attempt their capture

or to bring them crashing down,

in turn, other engineers
developed new defensive systems

to thwart whatever
was thrown at them.

Castles became symbols of
power and places of rebellion,

ultimately, super
castles couldn't compete

with a form of firepower

that could cause
destruction with one blast.

But thanks to the
robust engineering

behind their construction,

many medieval castles
are still with us today.

They're now big business,

allowing visitors
to step back in time

and marvel at the engineering
prowess of a bygone age.

- I think there is something

that speaks very immediately
and directly to us,

from childhood onwards,

about living in a castle
or defending a castle,

or besieging a castle.

So, for me,

there's no quicker route
back to the Middle Ages,

that vanished world, than there
is to go and visit a castle.

[dramatic music]