Original subtitles

We are surrounded

by extraordinary feats of engineering,

constantly pushing the boundaries of what's possible.

Without engineering, there'd be no modern world.

Gigantic cities, amazing infrastructure,

and ingenious inventions.

Engineering is the key to turn dreams into reality.

To reach these dizzying heights,

today's technology

relies on breakthroughs made by ancient engineers.

It's mind boggling how they did this.

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.

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.

Now it's possible to unearth the secrets

of the first engineers.

They managed to construct edifices

that have survived the ravages of time.

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.

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.

Globally,

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

We want to be secure.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Below the motte, the bailey was built.

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.

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.

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.

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.

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.

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.

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.

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.

The forecastle

is designed to protect a castle's entranceway.

In any fortification,

the weak point is always gonna be the entrance.

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)

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.

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.

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.

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.

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.

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.

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)

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.

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.

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.

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.

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.

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)

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.

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.

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)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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)

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)