Original subtitles

the largest museum in the world,

visited by more than 10 million people every year.

This immense building covers a vast 243,000 square metres,

making it the largest architectural assemblage in France.

Today, the Louvre is known for its Pyramid,

a monumental structure of glass and steel.

But since its origin,

the palace has seen exceptional technological innovation.

Eight centuries of architectural advances

that have transformed a simple royal residence

into the largest museum on the planet.

The Louvre is one of the most famous monuments in the world,

but it is also one of the most mysterious.

And it still hides construction secrets.

By scanning the palace,

from the satellite and aerial scale to the molecular scale,

scientists can now unravel the greatest mysteries of the Louvre.

Investigators will use an advanced drone for the first time.

And conduct 3D laser surveys of the structure...

..to reveal the secrets hidden behind the Louvre

completely invisible to the naked eye.

Technology will unlock the mysteries of the Louvre's construction

and reveal the genius of its architects,

exposing the incredible link between the museum

and the greatest monuments of Paris.

How did builders construct one of the world's largest palaces

in the heart of Paris?

What construction techniques are hidden within the palace's walls?

What technical innovations allow engineers to tunnel just 15m

beneath a building that houses many priceless treasures?

History, science, engineering

exposed as never before.

The Louvre Palace finally reveals itself on every scale.

The Louvre is an architectural masterpiece in the heart of Paris.

It is one of the largest palaces in the world

and occupies a big part of the capital's centre.

How did builders construct such an immense structure

in one of the most densely populated cities in the world?

Today, satellite images make it possible

to visualise the monument's oversized plan in its entirety.

The Louvre Palace and the neighbouring Tuileries estate

cover 42 hectares,

the equivalent of 40 football pitches.

So how did builders, over eight centuries of evolution,

construct one of the largest palaces on the planet?

To understand how this monumental structure came into being,

it's necessary to go back to the source of the monument

and investigate the mystery of its origin.

A few metres below the monument,

researchers have uncovered finely cut foundations

dating back to the 12th century.

This exceptional masonry from the Middle Ages

is evidence of the very first building of the Louvre.

These archaeological discoveries shed light on the Louvre's origin.

Now, 3D modelling exposes what the building looked like

in the Middle Ages.

Ancient builders constructed the fortress

as a square military building, with walls spanning 80m.

They defended its walls with circular towers,

and built a 30 metre-high keep at its centre,

a symbol of royal power.

The foundations are evidence of a fortified castle

built 800 years ago by a French king called Philip Augustus.

What's surprising is that the same fortresses,

with the same plan and similar construction principle

can be found in cities all over France.

So why did so many fortified castles in France

copy the chateau du Louvre?

The answer to this riddle

lies in examining the structure at a macroscopic scale.

Geologists want to determine the origin of these building stones.

Examining the stone at a macroscopic scale

exposes mysteriously-shaped marks.

Engravings of crosses, triangles or even hearts

can be seen all over the masonry.

These marks reveal how builders

ensured efficiency at each stage of the construction

of this monumental fortified castle.

The building site is gigantic for the end of the 12th century.

For the first time in France,

King Philip II's engineers design a construction method

that can be easily reproduced.

The first Louvre was built in just ten years,

an astonishing feat for this period of the Middle Ages.

From the very beginning of its construction,

the Louvre has been a fortress of impressive dimensions.

It served as a model for the King's castles,

but it is still far from the scale of the present Louvre.

Examining the site on the satellite scale

exposes the difference in size.

So how and why did builders upgrade the imposing Middle Ages fortress

to build one of the world's largest palaces?

The first step in this metamorphosis

was to transform a defensive castle

into a residence suitable for a king.

A branch of the palace known as the Lescot wing

is the only building from this era still visible today.

But at first glance,

there is nothing to differentiate between the periods of construction.

Examining masonry at the macroscopic scale

reveals the construction techniques used in the Renaissance.

This Renaissance-era masonry technique

has been found in all stages of the palace's construction.

Builders used this hard stone for the bases of walls and windows,

the parts of the structure most susceptible to weathering.

But they used a different, softer rock called Oise stone

to make up the bulk of the palace buildings.

The royal residence, although upgraded,

was still the same size as the original castle.

So how did the palace transform from a 6000-square-metre castle

into a building 20 times larger today?

Why and how did this royal residence

become the largest palace on the planet?

Now investigators have discovered that the fate of the Louvre

is linked to a building that no longer exists today.

The remains of this building can only be seen with radar technology.

Today, Thibault Sevenet is exploring the west end of the building.

He wants to investigate the soil

underneath the so-called 'tile gardens'

using geostatic radar technology.

The antenna sends a magnetic field into the ground

and a receiver records the signal that returns.

Very quickly, the radar locates hidden remains several metres...,

foundations located between the two wings of the Louvre Palace

over a distance of nearly 250 metres.

Examining satellite images

exposes the contours of this ancient lost palace.

This is the Tuileries Palace,

commissioned in 1564

by the Queen Mother Catherine de Medici,

for her personal use.

She decided to build her home 500m west of the Louvre castle,

on the outskirts of Paris,

in an area that was still countryside at the time.

The royal residence is located on one side of the Louvre,

and on the other, the castle built by the Queen's mother.

It was King Henry IV, more than 400 years earlier,

who decided to link these two castles

and transform an entire district of Paris

for a single purpose -

to build the largest palace in Europe.

Henry IV ordered the Great Gallery,

a 460 metre-long and 13 metre-wide building,

to link the two palaces.

It was a huge and unprecedented construction project for the time.

This new work increased the Louvre's surface area.

The dimensions are breathtaking.

From the foot of the monument,

it's almost impossible to see the end of it.

For two centuries, the Louvre was steadily expanding.

The gigantic size of the project

required huge financial and labour resources.

But how did the builders supply stone to such a huge project?

The quarries in Paris and Oise were no longer sufficient.

In 1870, the Louvre Palace was finally completed.

At the time, it was the largest building in France,

covering 135,000 square metres of the capital.

Thanks to the construction of the Tuileries Palace,

which long ago burned to the ground,

the first Louvre castle was transformed over centuries

into a royal palace

that is the largest monument ever built in Paris.

Today, the 243,000 square metres of the Louvre

houses a treasure trove of architectural masterpieces.

During each period of construction,

builders tried to outdo each other in technical prowess

as they enlarged the monument.

But what hidden technical innovations

allowed architects to make the Louvre appear as if it was built in one go?

Clues to this mystery lie in examining the construction

of key parts of the Louvre,

starting with one of the oldest parts,

the reception room of the Lescot Pavilion.

It's one of the most remarkable rooms of the Renaissance Louvre,

a ballroom as large as three tennis courts.

Its dimensions are astonishing, even today.

But there's something strange about the layout of this room.

This is a sign that these vaults were added

after the original construction.

But why?

A 3D reconstruction exposes the evolution of the building.

King Henry II wanted this reception hall

to be as large and as high as possible,

to dazzle his distinguished guests.

His architects chose to install a wooden ceiling.

The original grand reception hall had a ceiling over 15 metres high.

The builders would have to find a new way to support the ceiling.

In another, less well-known part of the building,

there are more hidden architectural secrets.

The best way to expose them

is to examine the structure on a satellite scale.

With the disappearance of the Tuileries Palace,

and the creation of the Pyramid as the entrance to the museum,

the layout of the Louvre has been transformed.

But a monumental and grand entrance to the Louvre Palace

has long been forgotten.

The monument is immense - 170 metres long,

with 52 columns on the facade that are almost 12 metres high.

How did the builders manage to assemble these stones

and make sure they would stay standing?

So how did the builders achieve this architectural feat?

Clues lie high up on the underside of the colonnade.

Access to the roof of the Louvre is tightly controlled,

but it's the only way to study the masonry's hidden engineering.

The latest technology can be used to reveal what is hidden inside.

The 3D reconstruction of the structure

exposes the full extent of the challenge.

Engineers chose a technique that would reinforce the stone.

They used iron as a framework for the stone elements,

ensuring the stability of the structure.

The Louvre Palace hides daring and innovative techniques

at each stage of its construction.

The latest monumental achievement,

the glass pyramid, built in the 1990s,

also conceals some well-kept secrets.

This monumental structure is 21 metres high

and made entirely of glass and steel.

Now, for the first time since its construction,

a technical drone is being used to inspect the building.

The drone takes 2500 photographs on each of the four sides,

recording detail down to 0.2mm.

A 3D scan exposes the first secret of the Pyramid's construction.

It's formed from 603 panes of glass,

95 tons of steel

and 105 tons of aluminium -

heavier than a passenger jet.

It covers an area of more than 1000 square metres.

But this pyramid is just a small part of a hidden technical wonder.

The true scale of the technical challenge

can only be revealed on a satellite scale.

Nearly 100,000 square metres of surface area was developed,

including an underground avenue 1.5km long and 4m wide,

which connects each of the historic wings of the palace.

The Pyramid sits atop an underground city built 30 years ago.

It represents just a small part of the full construction at the time.

Its position in the very centre of the Napoleon Courtyard

underlines the genius of the builders of the Louvre.

Evidence suggests that the architects of this palace

planned the layout so that it would provide

a remarkable view for onlookers.

The Louvre is a unique monument,

once a huge royal residence,

now the largest museum in the world.

This imposing architectural ensemble on the banks of the River Seine

is anchored by the Pyramid,

an architectural jewel which shines in its heart,

the centre point of a breathtaking view.

The Pyramid and the Arc of the Carrousel

seem to line up with the obelisk of the Place de la Concorde,

the Champs-Elysees,

the Arc de Triomphe,

and finally, the Arche de la Defense,

a perspective of almost 8 kilometres.

This view is considered one of the most beautiful in Paris.

How did the builders achieve such a feat?

What's the secret behind this lack of symmetry

in one of the most emblematic monuments of France?

On a satellite scale,

there's a clear 6% misalignment of the Louvre,

a discrepancy so large that it cannot be a calculation error.

So why did the architects plan the building like this?

Geo-radar technology reveals that

the Tuileries Palace had imposing dimensions - 260m long,

so it completely obscured the Louvre to the west.

Today, there is nothing left of this iconic palace.

In 1871, during a revolt against the ruling power,

the palace was completely destroyed by fire.

But fortunately, some elements of the Tuileries Palace survived.

Neguine Mathieux is the Director of Research at the Louvre

and joins Amelie Methivier, a stone restorer,

to visit the ditches of the Great Colonnade.

Neguine is in charge of securing the key to this vaulted room

and for good reason.

This room contains an invaluable treasure, kept out of sight.

Analysing these remains exposes the ferocity of the fire.

The disappearance of the Tuileries Palace

gave the Louvre a new layout.

Examining the site on a satellite scale

reveals that the axis of the former Tuileries Palace

corresponds perfectly to the historical view of Paris.

The architect has planned the layout in relation to the Tuileries Palace,

and not in relation to the Louvre.

But the satellite-scale images

show that this is not the only part of the palace which is asymmetrical.

Its wings follow two different axes, which are not parallel.

On one side, the Great Gallery,

which follows the course of the Seine,

and on the other side, the Richelieu wing,

which has to fit around the layout of the streets of Paris.

The result - the Louvre's plan is irregular.

So how did architects conceal the anomaly?

Once again, they resorted to a simple but effective trick.

The architects' stroke of genius corrected the error of symmetry

when viewed from the centre of the Louvre.

Many technical and architectural innovations were made

during the construction of the palace.

But as the building neared completion,

the Louvre would undergo a new metamorphosis.

It is known today as the largest museum on the planet.

The Mona Lisa, the Wedding of Cana - priceless works of art

are admired by more than 10 million visitors each year.

In the 18th century,

when it was decided to turn the palace into a museum,

the rooms were small and dark,

reserved for the king and his court.

So how did architects radically change the use of these buildings?

How can a royal residence

be transformed into one of the largest museums ever built,

capable of housing priceless works of art and millions of visitors?

From ground level at the Louvre,

there are few clues to expose

the transformation from a royal palace to a museum.

But satellite images reveal

a radically different view of the Louvre.

All the roofs have been opened up.

Glass canopies cover most of the museum.

How were these openings created?

The glass canopies provide a natural lighting source

that revolutionised the design of museums throughout the world

at the end of the 19th century.

Investigations on a macroscopic scale

reveal that the frames are built entirely of metal,

to support the glass canopies,

as seen at the top of the Daru Pavilion,

one of the highest in the Louvre,

which lights a monumental staircase.

Engineers built 10,000 square metres of glass roof.

But how did this revolutionary idea of opening up the ceiling

and creating metal frameworks come about?

Clues hidden in some structures

reveal that it all began at the Louvre.

Examining the building on a satellite scale

exposes a unique glass roof, today inaccessible from inside.

The reconstruction of this framework in three dimensions

reveals the historical structure.

The framework of the Salon Carre measures 23m by 15m.

It supports a central glass roof of 13m by 5m,

and is formed from 16 tons of wrought iron.

By analysing the steel structure and checking ancient documents,

experts realised that it is

the oldest surviving example in the world,

an icon of engineering built DURING the French Revolution.

The choice of wrought iron for these frames

was a technical innovation at the time.

This framework is one of the first prototypes

of a metal-structured glass roof -

an innovative concept that would inspire museums all over the world.

Despite the gigantic size of some rooms,

such as the Great Gallery or the Caryatids' Hall,

there is a lack of space in the museum,

especially to house monumental statues.

Clues to how architects solved this problem

are revealed by examining the building on a satellite scale.

In the '90s, architects decided to cover the surface courtyards

and turn them into huge exhibition spaces.

3D modelling techniques expose the detail

of this lightweight structure formed from 14cm-wide steel tubes

and supported by a network of stainless steel cables.

The final challenge for architects

was making it invisible from the ground,

in order to respect the architectural integrity

of the Rue de Rivoli in the centre of Paris.

The problem of lighting the museum was solved.

But there's still another difficulty.

In this museum,

only a tiny proportion of all the objects are on display.

For every square metre of space used to show works of art,

at least twice as much invisible infrastructure is needed.

The Louvre needed storerooms, laboratories, offices, workshops.

But none of this originally existed,

so engineers had to dig underground galleries.

Neguine Mathieux is exploring

the first basements created in the Louvre.

This underground city was built at the end of the 19th century

to allow the museum to function properly.

In this maze of secret corridors,

some spaces have been abandoned and forgotten.

These historic underground passages

are proof that there are still unknown places to be rediscovered.

Investigating the Louvre's basements provides a glimpse

of the many layers of the monument's construction,

a series of innovations that make the Louvre's hidden underbelly

a mosaic of diverse building techniques.

The Louvre -

this stone colossus in the heart of Paris seems unshakeable.

But early on, the building did show signs of fragility,

especially the 460m-long gallery built on the banks of the Seine.

Any movement of the building

could cause more than just major structural problems.

Some areas of the Louvre

are built with priceless sculpted and painted decorations

that could be damaged by the slightest movement of the masonry.

When the human eye isn't enough

to monitor this 270,000-square-metre complex,

the latest technology is needed

to examine the monument in minute detail.

One of the newest methods of investigation is photogrammetry,

used today on one of the oldest

and most precious parts of the Louvre, the Apollo Gallery,

built perpendicular to the Seine in the 17th century.

Photogrammetry allows investigators

to create a precise 3D reconstruction of reality,

shedding new light on architectural and decorative features.

This 3D mapping of the Louvre

exposes the evolution of the old buildings

and helps engineers detect the slightest structural movement.

In some places, major cracks have been uncovered.

So what is the condition of the Louvre's foundations?

The foundations are inaccessible,

buried several metres deep under the building.

But today, science and technology make it possible

to detect the invisible and probe the impenetrable.

Now, an exceptional project is giving engineers the opportunity

to examine the underside of the palace.

Thanks to new construction techniques,

they will dig under the Visconti Courtyard in the heart of the museum,

and under part of the Grand Gallery

to create new exhibition room.

But the work has already begun.

At this exceptional construction site,

the latest technology is used to scan the ground

and examine the state of the foundations.

Engineers can't afford to take risks while digging under the Louvre,

one of the most renowned buildings in the world.

After analysing radar readings,

the team used core sampling at strategic points in the Louvre

to probe the subsoil of Paris.

The first revelation is that

the foundations are much shallower than expected.

A stone building of this height

usually requires foundations 3 to 6 metres deep.

But to investigate the current condition of the foundations,

it's necessary to change scale

and examine the stone using an electron microscope.

These fragments are from the core samples

taken from the basement of the Louvre

and will be examined on a microscopic scale

to determine their nature and properties.

Scientists use an electron microscope

to bombard an object with a beam of electrons,

the smallest particle in an atom.

The object is placed in a vacuum chamber,

and the wave-like characteristics of the electron

magnify the object's image,

allowing the scientists to examine the material at high resolution.

This microscopic study

exposes characteristics and structure of the stone

which are completely invisible to the naked eye.

The microscope exposes a second revelation

about the foundations of the Louvre.

The research team discover that

the concrete under the stone foundations is damaged.

This is a double threat for the Louvre.

Investigations reveal that

not only are the foundations extremely shallow,

but that the materials used at the time have lost their strength.

The banks of the Seine are particularly soft

and water infiltration due to bad weather and flooding

weakens the old concrete

and endangers some historic buildings.

Faced with these revelations,

the engineers must find a solution to consolidate the foundations

and secure this part of the museum.

Engineers choose a technique called jet grouting.

They drill several metres into the ground

and then spray in a self-hardening cement.

Hundreds of underground columns now reinforce

the eroded foundations of the Visconti Courtyard.

But even the most recent structures can show signs of fragility.

The Pyramid of the Louvre is an architectural gem,

a huge, 2000-square-metre glass roof

supported by a spider web of stainless steel.

To study the behaviour of this monumental structure,

investigators turn to advanced technology

that can expose whether the Pyramid is undergoing too much movement.

The team wait until the middle of the night

to take precise measurements using a laser scanner,

a technique known as lasergrammetry.

The 3D modelling reveals

that the structural elements of the Pyramid

can undergo deformations of several centimetres in a single day.

But the measurements also reveal

that the whole pyramid has notably shifted.

Built over eight centuries,

the Louvre is an iconic and unique monument

from the oldest foundations to the most recent structures.

The latest technology makes it possible

to study and protect this monument,

which many consider to be the true masterpiece of the museum.

The Louvre -

this palace of kings in the heart of Paris

is a testimony to architectural innovation.

Eight centuries of technical daring

that have transformed a fortified castle

into the largest museum on the planet.

The Louvre is a museum city,

a living structure with more than 2000 employees working every day

and 25,000 daily visitors who come to admire its works of art,

an immense machinery that doesn't stop.

Now, new investigative tools

have made it possible to explore this building's structure.

New technology is also raising fresh questions

about a monument that historians thought they knew well.

Surveying the basements of the Tuileries

will reveal the exact nature of the remains - maybe more -

perhaps discovering new forgotten rooms.

The Louvre's scale is immense, as are its component buildings,

whole sections of which aren't yet fully investigated.

A colossus of engineering,

a true architectural masterpiece

whose design was often ahead of its time.

Captions by Red Bee Media (c) SBS Australia 2022