The Lost City (La ciudad perdida)

Deep in the heart of France

is a mountain whose peak is now covered in woodland.

Yet it's here that over 2,000 years ago,

a powerful Gallic people built their capital, Bibracte.

There were hundreds of dwellings and workshops,

public buildings, prestigious houses.

Bibracte had over 10,000 inhabitants,

making it one of the largest cities in Gaul.

It's as if the settlement

was fossilized beneath the trees roots.

Thanks to excavations

carried out over several decades

and new imaging techniques,

archaeologists have discovered that some of the buildings

were directly inspired by the most prestigious buildings

in ancient Rome.

Unfortunately,

none of the buildings foundations remain.

In spite of that, we've been able

to roughly piece together its appearance.

You really get the impression

that this domus was bought off catalog.

The person who had it built wanted the very best

of what was being done in Italy at the time.

There was a double circle of ramparts

to protect the site,

an immense forum in the heart of the settlement,

like in the biggest Roman cities,

an ingenious system to manage the water for the thermae.

Thanks to a reconstitution of the city

when it was at its peak,

you will discover why Bibracte was unique

and why its inhabitants suddenly deserted it.

This is Bibracte,

the Gallic capital admired by Julius Caesar,

which was the first to enter the Gallo-Roman era,

over 2000 years ago.

In the 1st century BC,

people who consider themselves Celts

occupied a vast zone that stretched

from the Atlantic to central Europe.

Solely to the west of the Rhine,

there were probably around 10 million individuals

divided up into around 60 tribes.

They did not obey the same chief

nor did they speak the same dialect.

They did not form a nation,

and yet they belonged to the same cultural community

that we are accustomed to calling the Gauls.

Among them was a particularly rich and powerful people,

the Aedui.

The Aedui's location in the middle of Gaul

made them natural intermediaries

between the Romans on the one side

in the lands towards the Mediterranean

and the other people's of Gaul

in the lands stretching out to the Rhine.

And that was most certainly a great advantage for them

politically, of course,

but it also brought them great subsidies

of a financial nature, in particular,

from the sale of wine and, why not,

from the sale of slaves or various materials.

That was most certainly one of the sources

of the Aedui's wealth.

Their vast territory,

which was ideally situated between the Saône and the Loire,

facilitated trade at a time when rivers

were the main routes of communication.

We know that the Romans were very interested

in Aedui's strategic position on these communication routes,

to the extent that they signed a military alliance treaty.

And it was very, very rare for the Romans

to sign such treaties,

so we can see how important they considered Aedui to be.

And it was in the Morvan,

in the vast heart of the territory on Mont Beuvray

that the Aedui would prove their expertise

and resourcefulness in building their capital,

Bibracte.

For 2000 years, Bibracte remained there,

dormant, invisible to all,

beneath the vegetation of the thick beech forest.

The first remains were discovered there

a century and a half ago, and since then,

archaeologists have unearthed

countless traces left by the Gauls.

Hundreds of thousands of objects, remains of dwellings,

of water supply systems,

and even the vestiges of exceptionally large buildings.

One of the main challenges for us

was to detect the remains of a major archeological site

that had been fully preserved beneath the forest.

What is the most interesting for us,

is that there has been very little subsequent reoccupation

to disturb the constructions from the Gallic period,

which makes Bibracte an observatory of Gallic society

that is practically unique in France and in Europe.

According to Julius Caesar himself,

Bibracte was the largest and most important oppidum

in the Aedui's territory.

Oppidum is a Latin word

regularly used by Caesar

to define the Gauls fortified settlements.

So for convenience,

archaeologists decided to keep Caesar's term.

The Aedui settled here

because the site offers a number of advantages.

Mont Beuvray culminates at 820 meters above sea level,

has extremely steep slopes and is difficult to access.

Above all, its summit can accommodate

a large population at high altitude.

It's an absolutely remarkable belvedere

that looks out over gigantic landscapes

that stretch out for up to 200 kilometers,

as far as the Alps that allows you to immediately understand

why the Aedui chose to settle on this hill.

It is in fact, because they had an impression

that they were on the top of the world.

There were definitely military considerations

behind their settlement here in a period

that was visibly unsettled.

The site covers 200 hectares.

That's the equivalent of 300 football pitches.

And for several decades,

archaeologists have been trying to discover

what Bibracte looked like at the peak of its splendor.

The settlement was immense, 200 hectares.

That's almost two kilometers from one end to the other

without counting the areas beyond the fortifications.

So there's no way we can excavate everything.

That would take hundreds of years.

Gradually a certain number of techniques have appeared

that allow us, to a certain extent,

to understand what is buried below

without having to move the earth.

Among these innovative

and non-invasive techniques is LiDAR surveying.

Contrary to radar, which uses radio waves,

LiDAR uses light waves from a laser.

With this technology onboard an airplane,

we can see the exact and detailed variations

in a site's topography.

What's interesting with this sort of survey

is that it allows us to obtain a detailed image

of the topography beneath the forest canopy,

meaning below the vegetation under the trees.

So what is impossible to see from a traditional aerial image

suddenly becomes fully visible.

You can clearly see the relief, the valleys,

the summits, the peaks of Mont Beuvray

but also whole set of anomalies,

corresponding to the archeological remains

that are preserved and fossilized

in the form of micro reliefs beneath the current vegetation.

In particular, the confirmation of the layout

of Bibracte fortifications that we can see very clearly

in the shape of these lineaments.

But we were also able to map out precisely

a whole area of ledges and terraces

that are zones that were much more conductive

to the installation of Gallic period constructions

and of the settlement's monumental architecture

in the main occupied areas of Bibracte.

Whereas the first excavations

showed that Bibracte was surrounded

by 5 kilometers of fortifications,

LiDAR surveying revealed that the fortification system

was in fact much more complex.

Initially, another fortification,

the founding act of the oppidum,

ran for over seven kilometers.

The outer wall,

the longest one, is older than the inner wall

and the inner wall is most likely a reduction

of the outer wall, probably for military reasons.

The aim was probably

to reduce the area to be defended

by decreasing the oppidum's surface

from 200 to 135 hectares.

Bibracte was most probably

one of the first Celtic oppida that Caesar discovered

when he started his military campaigns, precisely in 58 BC.

You have to imagine that the settlement

was visible from a great distance,

at least 30 kilometers away.

It was a settlement perched up on its hill

and surrounded by fortifications.

As you drew closer,

you could see the very unusual style of the ramparts.

The archaeologists were astonished

to find themselves with a construction

precisely described by Julius Caesar himself

in his "Commentaries on the Gallic War",

that he wrote in part at Bibracte.

He called this structure Murus Gallicus, the Gallic wall.

The Murus Gallicus is generally built

in the following fashion.

Straight beams are placed at equal distance from each other,

two feet apart on the ground,