In France,
in the centre of Paris stands the Louvre Palace, the largest museum in the world, visited by more than 10 million people every year. This immense building
covers a vast 243,000 square meters, Making it the largest
architectural assemblage in France. The Louvre is a palace
that has few equivalents in Europe or the world. 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. The palace itself is the very first work
of art presented to visitors... Eight centuries of architectural advances
that have transformed a simple royal residence, into the largest museum on the planet. We took the best architects,
we took the best stone, and we put a lot of money
into building this monument. 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. The Louvre may seem like a very well-known palace,
but that doesn't mean that if you look, there isn’t a lot new to discover! By scanning the palace from the satellite and aerial scale to the molecular scale scientists can now unravel
the greatest mysteries of the Louvre. We make the building speak by using means
that let us visualise the infinitely small, and make the material and its most intimate
aspects speak for themselves. Investigators will use an
advanced drone for the first time... We fly extremely close to the pyramid,
as close as three metres, so it's quite complicated... and conduct 3D laser surveys of the structure. It's accurate to a thousand of a degree. To reveal the secrets of the Louvre,
completely invisible to the naked eye. New technology will bring
answers and expose secrets. Technology will unlock the mysteries
of the Louvre's construction, and reveals the genius of its architects... exposing the incredible link between
the museum and the greatest monuments of Paris. It seems very hard to imagine, but this lining up
of the view was not possible in the past. 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 15 metres, beneath a building that houses
many priceless treasures? Digging so close to the heritage collections, and to a work as important as the Mona Lisa It's completely crazy! 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 capitals 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... The very first Louvre
no longer exists on the surface. So it’s necessary to go down into the depths, as it were, to discover it... 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. This is the heart
of the medieval fortress of the Louvre. Here we are in the dungeon's ditches, ditches that were dry and paved and which surrounded
the imposing central keep of the courtyard. So it was 15 metres in diameter. 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 80 meters. They defended its walls with circular towers
and built a 30-meters 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. It’s really the implementation
of a new style of castle called Philippians like Philip Augustus. There are as many as twenty castles that copy, sometimes with variants,
this style from the Louvre. So why did so many fortified castles in France copy the Château 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. This is quite typical of the stone of the period, the stone of Paris is heterogeneous. You can see beds of marine fossils here, see? We’re looking at stones which were extracted
in the quarries of the 13th district, or arrondissement, of Paris. 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 engraved hearts are marks
carved by stonemasons in the quarries during the manufacture of the blocks, before they were transported to the Louvre
and installed at the building sites. The aim was for the stonemason to be able
to be paid for each block of stone he made, and the whole procedure shows
the sophistication of the Louvre building site. 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. Their idea was probably to define
a number of model structures. Above all, a great deal of attention was paid
to the organisation of the building site to make this construction
as efficient as possible. The first Louvre was built in just 10 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. In the Middle Ages, the castle was only a quarter the size
of one of the courtyards of today's Louvre, the square courtyard. 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. The great evolution is the moment
when they decided to destroy, piece by piece, the Louvre of the Middle Ages,
to create a truly modern residence. And this is the work of the Renaissance
in the middle of the 16th century... 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. We’re here in the square courtyard of the Louvre. Under our feet are the remains
of the medieval castle of Philip Augustus and we have the Renaissance buildings by Lescot. Examining masonry at the macroscopic scale reveals the construction techniques
used in the Renaissance. It’s Paris stone with a fine grain, it’s hard... it’s resistant and therefore they mostly
use it for wall bases, masonry bases... Here we see the Paris stone, up to here... and above -stone from l’Oise, which has a coarser grain
that is more yellowish... It is a marine limestone,
which is the same age but which is coarser, but it’s a firm limestone which constitutes
the main part of the masonry of the Lescot wing... 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 meter 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, Thibaut Sevenet is exploring
the west end of the building. He wants to investigate the soil underneath the so called ‘tile gardens’
using geo-static radar technology. We’re carrying out geo-radar measurements using a device that sends
electromagnetic probes into the ground to analyse everything in the subsoil
to a depth of three or four metres. The antenna sends a magnetic field into the ground and a receiver records the signal that returns. We're trying to detect remains
in the area of the former Tuileries Palace, which could potentially lie
in the first two or three metres. When doing archaeological research
on a monument that is a few centuries old you can find foundations and you can
sometimes find empty cellars. Very quickly the radar locates
hidden remains several meters deep... 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
500 meters west of the Louvre castle, on the outskirts of Paris, in an area
that was still countryside at the time... You have to realise that the Louvre and the Tuileries were two
completely separate palaces at first, that had little to do with each other. Until King Henri IV decided
to link the two palaces by a large gallery alongside the Seine. The royal residence is located
on one side of the Louvre and on the other
the castle built by the king's mother. It was king Henry IV, more than 400 years ago, 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. This is called the grand design. It’s an extremely ambitious project,
but also a very difficult project to carry out, because between the two palaces, here was a whole area of city
that they needed to evacuate and destroy. Henry IV ordered the great gallery - a 460-meter long and 13-meter wide building
- to link the two palaces. This new work increased the Louvre surface area. This new work increased the Louvre surface area. The dimensions are breath-taking... from the foot of the monument
it’s almost impossible to see the end of it... And the kings didn’t stop there, to succeed in giving order to this area there’s this big wing
which stretches alongside the River Seine. It was Napoleon who would launch
the idea of a second wing that would run along the Rue de Rivoli, which he started work on and which would be
finished by Napoleon the third. 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. The demand for stone was enormous and so they were calling on quarry
sites further and further away. Ideally the stone was transported by river. But with the advent of the railway,
everything changed. Stone could be transported from quarry sites
that were far from rivers and streams, so stone from anywhere in France could arrive
in Paris without a problem... In 1870, The Louvre Palace
was finally completed... At the time, it was the largest building in France covering 135,000 square meters of the capital. The Louvre is a very long-term project
that spans almost 800 years. It's a situation that has no real equivalent
in any other building in Europe. It is a seed that has never stopped growing
due to the will of the various sovereigns, then of the emperors who succeeded one another
at the head of the French State and finally, it represents the heritage that we’ve now known
since the end of the 19th century... 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 meters 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... When you arrive in the building, you have the impression that everything
we see today was built at the same time. But in reality, this is the result of a long evolution
and of major transformations. 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... The Caryatids' room is a good example
of the Louvre’s mystery whole which seems coherent,
homogeneous, magnificent, but which is the result of a history
that is much more complex. 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. If you look closely at the vault, you can see that it’s supported by pillars. These pillars are hidden just behind columns
that are placed in the corners. 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. This vault gives the impression
that it’s always been there and in fact that’s not the case at all! In the beginning, there was a ceiling with beams. It was simply a very long span ceiling, as there were almost 14 metres
between the two walls. They placed 14 beams 14 metres long and two and a half metres apart, braced by corbels, to support the ceiling. The original, grand reception hall had a ceiling over 15 meters high. But over time a problem emerged. There was another room directly
above that was often busy. Under the weight of numerous courtiers
- it collapsed. The builders would have to find a new way
to support the ceiling. They decided to make a low stone vault, not very high, but a vault that would rest on
masonry blocks that would be raised. Here we see the genius of the French architects, who worked in succession to improve the structure. 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... One of the most innovative places
in the history of the Louvre's architecture is what is known as the Colonnade du Louvre It’s a building that we don't look at much today because it seems to be the back of the Louvre. But you have to understand that
at the time of the French kings, the layout was completely the opposite. It’s true that this great facade, which is truly remarkable, is little known, but it’s a great piece of architectural bravery. The monument is immense:
170 meters long with 52 columns on the facade that are almost 12 meters high... How did the builders manage
to assemble these stones and make sure they would stay standing? At the time of Louis the 14th, this was one of the most remarkable
building sites of his reign. The project of the century in terms
of technical prowess and construction, the lifting of large monoliths, large stones. So how did the builders achieve
this architectural feat? Clues lies 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. We’re here in the part
which is above the supporting columns, so in the part just above the columns
but inside the actual facade. So, what we see
here is part of the metal structure that helps to reinforce the whole of this facade and what’s exceptional on this facade is to have done it
on such a scale and at such a time... 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. There’s metal absolutely everywhere... and so this architecture is a trick, because from the outside, it looks like cut stone, like used in antiquity. But in reality, iron plays an absolutely essential role. 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 principle of reinforced stone is to give the rock mechanical characteristics
that it doesn’t have naturally, because otherwise
stone works very well under compression, but not well under tension. So the Louvre is quite an
exciting piece of architecture, because it’s sometimes a little misleading. What you look at and what you notice first is not necessarily the most important thing. 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... The pyramid is a superb structure that represents the architectural
audacity of its designer. The pyramid gave rise to an extremely intense
debate at the time of its creation. It’s a radically modern form. This monumental structure is 21 meters 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... This is a drone configured for industrial work. There are quite a few sensors that can be used in case of problems... This is a once-a-day operation. In the past it was done with rope climbers
abseiling down from the top of the pyramid and this is the first time we've done it by drone. We fly extremely close to the pyramid, as close as three metres, so it's quite complicated... We have obstacle detectors on the drone but the pilots are trained
to fly very close to the structure and we try to leave nothing to chance. And so we've automated it and have
pre-defined routes that the drone follows. We have a pilot who monitors the drone, he’s there to take care of the images
and to make the drone back off if it flies too close to the pyramid. The drone takes 2,500 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 1,000 square meter. But this pyramid is just a small part
of a hidden technical wonder... The most exceptional part of the pyramid
isn’t what you see from the outside. It's what you see when you’re underneath... When you walk in the carrousel today
you get the impression that that’s it but in fact,
three quarters of the space is hidden. It looks one way on the top, but then you realise
that’s just the tip of the iceberg. The true scale of the technical challenge can only be revealed on a satellite scale. The pyramid is just a small element. You need to remember that almost the entire
Napoleon courtyard was excavated, plus a large part
of the underground Carrousel mall. The construction of the pyramid
created an access point for visitors to the museum, and made it possible to develop
a whole range of underground services - even a small shopping mall which was created when this project
for the Grand Louvre was completed. Nearly 100,000 square meters
of surface area were developed, including an underground avenue
1.5 km long and four meters wide which connects each
of the historic wings of the Palace. The contrast is absolutely striking between the Louvre of today
and that of 150 years ago. 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 Napoléon Courtyard underlines the genius
of the builders of the Louvre... Evidence suggest 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 breath-taking view. The pyramid, and the arch of the Carrousel, seems to line up with the obelisk
of the Place de la Concorde, the Champs Elysées, the Arc de Triomphe
and finally the Arche de la Defense... a perspective of almost eight kilometers! This view is considered
one of the most beautiful in Paris. How did the builders achieve such a feat? When you look at this view... you get the impression that
the whole Louvre Palace is perfectly symmetrical but in fact that’s not at all the case! 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? This lining up of the view wouldn’t have been possible until 1871 because a palace, the Tuileries Palace, once stood between the two wings of the Louvre. Georadar technology reveals
that the Tuileries Palace had imposing dimensions, 260 meters 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... Néguine Mathieux is
the director of research at the Louvre and joins Amélie Méthivier, a stone restorer, to visit the ditches of the great colonnade. Néguine 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 You can find the remains
of the Tuileries Palace here... one of the most important palaces
in the history of France and also in the history
of architecture in France... The Tuileries Palace had an amazing history. It burned for several days and the ruins
remained for more than ten years... Analysing these remains exposes
the ferocity of the fire. Here, the stone has broken
up a little into slabs and eroded. It would seem that this is due to the strong heat that these stones were subjected
to at the time of the Tuileries fire... Even when the fire went out it wasn’t possible to get close
because the heat was so strong. The disappearance of the Tuileries Palace gave the Louvre a new layout. This fire changed
the face of the Tuileries Palace of course, but also of the Louvre Palace
and even the city of Paris. We had a very closed imperial city under Napoleon and this destruction
finally opened the palace to the city. 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 architects planned the layout
in relation to the Tuileries Palace and not in relation to the Louvre. So the view, as we see it today,
isn’t the one that was originally conceived, since it was planned for a palace
that no longer exists! And the disappearance of the Tuileries
has allowed the Louvre views towards the city in an extremely broad way, because the perspective allows
the Louvre to be projected very, very far into the city. 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... This is the great work
of the 19th century architects who were obsessed by the idea of making us
believe that everything is regular and so the solution they find to this problem
is to create an optical illusion. The courtyards located on the Seine
are perfectly rectangular while the courtyards, which are located between the left side of the
pyramid and the Rue de Rivoli, they have a trapezoid shape. So we’re not aware of it
when we are around the pyramid, when we approach the area from here, but in fact it’s a rather clever trick. You have to have
a very sharp eye to realise this... 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 millions 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... Among the Louvre's most important metamorphoses is the transformation of
a royal residence into a museum. The creation of the museum dates to 1793. It was really at the end of the 18th century that the royal palace
was transformed into a museum and the question arose of lighting
to present the works to the public. 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? The history of the Louvre is a true history
of architectural innovation in Europe. 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 rooves have been opened up. Glass canopies cover most of the museum. How were these openings created? Here we are under the rooves of the Louvre... under beams and a glass roof.
Which are quite modern because they’ve been wired for electricity and further along there are older beams and a glass roof from the 19th century. They decided that the best light came from the sky it’s a diffused even light... So they had this very original idea
of making holes in the ceiling... What’s interesting here... is that next to the wooden frame
we have a steel frame, a canopy and finally an oculus giving
indirect light into the room below us... 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. This steel structure, in its workmanship, is characteristic of frames built
in a number of rooms in the Louvre for natural lighting during the Second Empire. Engineers built
10,000 square meters 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 3
dimensions reveals the historical structure... ...the framework of the Salon Carré
measures 23 by 15 meters it supports a central glass roof of 13 by 5 meters and is formed from 16 tons of wrought iron. The glass roof of the
Carré Lounge is a real originality. It's a novelty that
we only realised quite recently. 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 steel structure of the lounge was actually created in 1789. It's quite incredible because the engineers
were working on the metal frame at the same time
that the Bastille was being overrun! The choice of wrought iron for these frames was a technical innovation at the time... They were obsessed with the question of fire... There was only one way
to protect works of art from fire, wood was banned completely! And so at the Louvre they were going
to test some of the first metal frameworks in existence in France... 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 nineties, architects decided to cover the service courtyards and turn them into huge exhibition spaces. So here we are, at a much more contemporary roof that was made at the time of the work
on the Grand Louvre in the 1990s. It’s a technical feat
to have been able to cover this roof because of it’s incredible dimensions. 3D modelling techniques expose
the detail of this light-weight structure, formed from 14cm wide steel tubes and supported by a network
of stainless steel cables. We have dimensions of 60 meters by 40, that’s to say a little more
than 2000 square meters... It’s a feat of engineering because the walls of this courtyard
are not parallel to each other... The covering above here
must cancel out that problem of parallels. 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 meter 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... Every time you dig, you find remains and more history to be discovered. Néguine 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. We’re in the basement of the Louvre. We’re under the Venus de Milo room. This is under the ‘Vieux Louvre’, one of the oldest parts of the Louvre. There is a labyrinth of corridors, spaces that have been used for storage,
organisation and support for the museum. In this maze of secret corridors, some spaces have been abandoned and forgotten... Walking in the Louvre also means
discovering hidden spaces that are fragments of history. You walk along this Philip Augustus enclosure and you come across
a remnant of the Second World War. An anti-aircraft shelter has been dug here! These historic underground passages
are proof that there are still unknown places to be rediscovered. Every time we dig, as soon as we start,
we come across older remains. Every time we excavated we made a discovery! Today modern technology allows us to discover, without always digging, old remains that are hidden underground. 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 460 meters long gallery
built on the banks of the Seine... It should be remembered that part
of this gallery collapsed in the 19th century after very considerable movements... since then, there were surveys which showed that the walls had moved
more than 60 cm from their original position... 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. I often tend to think that the palace itself is the first work of art
that is presented to the visitors. This building must remain perfectly still. In a building such as the Louvre, the aim is to prevent any possible incident. The room for error
must be kept as small as possible. 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. We’re going to scan the walls
of the Apollo Gallery. This is a telescopic carbon pole that allows us
to raise the camera up 12 or 13 metres. So we're going to cover the wall by taking photos every 50 cm
to be able to do 3D modelling. Photogrammetry allows investigators to create a precise
3D reconstruction of reality... shedding new light on architectural
and decorative features... We use photogrammetry a lot
because we create an image, so we have a visual archive and in addition to photogrammetry
we have a geometric archive as well... We have the 3D model,
so we can examine it section by section, both horizontally and vertically,
and we have dimensions almost to the millimetre... 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? Some of the foundations were poorly known. We didn’t know how deep they were buried... 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... What’s interesting today, with modern radar technology, is that it offers us a non-destructive method to investigate foundations pillars, or walls to understand the structure. 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 rooms... The technical challenge of this project
is to dig 15m deep near the facades without risking the collapse of the pillars
that surround the courtyard and support the galleries
around the Visconti courtyard. Here’s the Mona Lisa
and the Visconti courtyard just behind... it's completely crazy. Nobody believed in it at first... Digging so close to the heritage collections and to a work as important as the Mona Lisa, with all the technical constraints
that it can cause... it's completely crazy! 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... It's precious, it's fragile... so we have to adapt to this reality, we’ve chosen a non-destructive method, a radar method which allows us to bring back
a certain amount of qualitative information on the constitution of materials and structures. You can really see what’s underneath. But the challenge with radar
is that you see things but you don't necessarily know what it is. 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
three to six metres deep... It was not at all expected to discover
that the foundations were very shallow... just 1.8 to 2 metres for some, that's almost the height of a person! Today it's inconceivable to imagine
that we could make a building that might move and eventually collapse. But this risk was probably taken
for granted during the Renaissance. But to investigate
the current condition of the foundations, it’s necessary to change scale, and examine the stone
using an electron microscope. The Louvre is here! In our hands we have samples from the foundations, from the Visconti courtyard of the Louvre. 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. These materials will be taken
and we’ll make them speak, we’ll test them, we’ll identify the stone, its load-bearing capacity,
its resistance to crushing and impact by the weight of the structures. 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 magnifies the objects image, allowing the scientists
to examine the material at high resolution... The usual magnification is from a few hundred
times to several thousand times, these are the most common techniques... but we can go much higher, up to 300,000 times... This microscopic study exposes characteristics and structure of the stone which are completely invisible to the naked eye. This electron microscope investigation technique
is key to highlighting symptoms. 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... The stones themselves
were in a rather satisfactory state, like any good Parisian limestone. But it’s the surrounding concrete slabs at fault. At the time concrete was
undoubtedly very badly prepared, it’s not the modern concrete that we know
- very compact and very closed. Here we’re dealing with a porous material. 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 Louvre is essentially
a colossus with feet of clay, from the point of view of its location. The palace is on the banks of the Seine... so therefore it’s built on sand... 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. Now we have extremely sophisticated
techniques for creating foundations that didn’t exist in the past, and in particular for hardening
the soil to some extent... Engineers choose a technique called Jet Grouting. Jet Grouting is the technique
of cement injection under pressure... 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 Court... All this is due to modern techniques which ensure a very good stability
to the most recent parts of the Louvre. On the other hand, for the older parts, obviously
the techniques were more rudimentary and a certain amount of risk remains... But even the most recent structures
can show signs of fragility... 30 is the age of the first wrinkles... We don't expect to find any serious symptoms, but from time to time it’s necessary
to make an inventory of the work and make an assessment to highlight work necessary for
its renovation and conservation over time. The pyramid of the Louvre is an architectural gem, a huge 2000 square metre glass roof, supported by a spider web of stainless steel. When you make a work of this type, you’re making a very large greenhouse and therefore you have
very significant thermal expansion, because the structure of the pyramid is exposed to temperatures
of 60 to 70 degrees in the summer. So the changes in temperature generate dimensional variation
and the structure changes. 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. It's a 3D scanner
so it will completely digitize the pyramid. The laser takes about a million points per second, it scans the lines continuously
and rotates as it travels, so we‘ll have a cloud of points
representing the pyramid in three dimensions. The pyramid,
between day and night, can get deformed. Especially during the day,
when the sun is shining, which alternately hits each
of the faces from east to west. So we do the measurements at night
so that we can measure when it isn’t moving. 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. Since 1989, it has settled down
a few millimetres at the base, so the whole structure
has dropped just a few millimetres. This is something that we track
because we’re on a slab that is huge, with huge overhangs. So, we have to keep track of these parametres. 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 is a permanent theatre
of experimentation even today. Architects try things, find solutions, experiment and have great success. The Louvre, this palace of kings in the heart of Paris, is a testimony to architectural innovation. The Louvre is a place of excellence, which means that engineers wanted to provide
what they thought was the best, even if it meant transforming
what had come before. Eight centuries of technical daring
that have transformed a fortified castle into the largest museum on the planet. The Louvre has always been
the scene of experimentation, technical and architectural innovations... from the medieval Louvre to the Pyramid
in the middle of the Napoleon courtyard... The Louvre is a museum-city, a living structure with more than
2,000 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 buildings structure. Today's methods make it possible
not to destroy, not to build, but to allow the discovery of hidden remains, using non-immersive means
that allow new stories to be told. New technology is also raising fresh questions about a monument
that historians thought they knew well... New technology will bring answers... but also expose secrets. Surveying the basements of the Tuileries will reveal the exact nature of the remains... maybe more? Perhaps discovering new forgotten rooms. Sometimes we discover things
that haven’t been seen for 2 or 300 years. When we find a room,
a hiding place - that's exciting! It's a job for which we have
devices that are almost like toys and which allow us to discover our inner child
when we find exciting results! The Louvre’s scale is immense,
as are its component buildings, whole sections of which
aren’t yet fully investigated... The Louvre is a monument, an extraordinary museum... It’s a historical patchwork
that has been built up over time, one after the other, one thanks to the other. A colossus of engineering, a true architectural masterpiece whose design was often ahead of its time... There have been a few
world premieres at the Louvre. Our wish is that there will be more. The pyramid is also a unique building. We’re at a palace that is eight centuries old
and is constantly innovating
