We begin at around the third millennium BC in Mesopotamia.
A good part of the population is already sedentary, practicing agriculture and animal husbandry.
But in the more arid zones, some people continue a nomadic way of life.
At that time, a 220 km long wall is built to separate the cultivated lands and the pastures used by the nomads.
This wall, barely more than one meter high, is made of dry stone and is relatively fragile.
It therefore probably does not have a defensive function per se,
but rather serves as a delimitation or border between two ways of life.
Around this same period, further east, the powerful Third Dynasty of Ur controls the Tigris-Euphrates basin.
But its north-western border is regularly attacked by nomadic Amorite tribes.
The king of Ur then builds a fortified wall, or possibly a set of defensive ramparts about 280 km long,
linking the Tigris and the Euphrates.
But Ur has other enemies, including Elam to the east who, in 2004 BC,
forms a coalition and seizes the capital.
The Amorite Wall then disappears without a trace.
Only ancient texts mention it.
If it did exist, its exact layout and composition are still unknown today.
In Asia, the king of Qin finishes unifying the surrounding kingdoms, and forms the Qin dynasty in 221 BC.
But in the north, nomadic Turco-Mongol tribes, called the Xiongnu, threaten.
The emperor then builds a Great Wall 6 meters high, replacing old defensive walls that became obsolete.
Tens of thousands of forced laborers are mobilized for the construction of the stone and clay structure.
It has, on the one hand, a defensive function,
and on the other hand it delimits the border between the external world, nomadic and onsidered barbaric,
and the internal world, unified and said to be civilized.
Later, the Han dynasty, after victories against the Xiongnu, extends the wall,
so that in the first century AD, it is 4000 km long, linking present-day Korea to the Gobi Desert.
In the second century AD, the Roman Empire is at its peak, controlling all the coasts of the Mediterranean basin.
The threat is then the peoples called barbarians, who live all around the empire.
Limes are built, that is to say, sets of roads, palisades, walls, watchtowers and ditches
that are adapted to the terrain, following ridges and linking rivers.
But they are not continuous nor homogeneous.
In 122, in the province of Brittany, the emperor Hadrian puts an end to the expansionist policy of his predecessors,
and builds a wall that bears his name, isolating the Celtic peoples of the north.
About 4 meters high, it is made of stone and peat and is bordered by ditches.
It is 117 km long and connects the North Sea to the Irish Sea.
A few years later, Hadrian’s adopted son Antoninus, after military campaigns,
pushes the border further north, and builds a new wall which also bears his name.
On the continent, other limes are built to push back the Germanic peoples.
The most important one links the Rhine and the Danube over a stretch of 550 km,
including hundreds of watchtowers and forts.
In total, more than 5000 km of limes are built all around the Empire.
Their function is mainly to prevent large population movements and military invasions.
However, since they are not totally hermetic and are located on the borders,
the limes gradually become places of commercial exchange between the Romans and barbarian merchants.
They attract more and more foreigners who come to settle near the limes,
including on the Roman side, without there being any conquests or invasions.
In Asia, at the beginning of the 13th century,
the Mongol Empire of Genghis Khan begins the conquest of China.
Despite the Great Wall, the Jin dynasty is invaded.
The Mongols then found the Yuan dynasty, which imposes itself on all of China.
The Great Wall is in the center of the empire and serves no more benefit.
But in 1368, after an insurrection, the Chinese chase out the Mongol power, and found the Ming dynasty.
But the Mongolian threat is still present in the north, and the Great Wall is rebuilt:
this time with stone and brick, and up to 7 to 10 meters high.
Towards the end of the 16th century, its construction is completed.
Hundreds of thousands of soldiers form permanent garrisons all along the Great Wall.
But its construction, its maintenance, and the permanent garrisons cost the empire dearly,
and the economy deteriorates, which provokes revolts.
In 1644, a rebel army seizes Beijing, which results in the emperor committing suicide.
But at the eastern end of the Great Wall, a general who remains loyal to the Ming
chooses to ally with the Manchus of the Qing dynasty, and opens the gates of the Great Wall to them.
The Manchus then impose themselves on the whole of China,
and extend their territory as far as present-day Mongolia, making the Great Wall obsolete.
During the Second World War, Nazi Germany, which dominates Europe,
fears an Allied military landing from Great Britain.
The Atlantic Wall is then built all along the European coast.
It is not a wall per se, but rather a series of fortifications,
mainly bunkers, but also minefields, and obstacles intended to block tanks.
But these constructions are not enough to prevent the largest military landing in history
that takes place in Normandy.
After World War II, the Cold War revives the construction of walls.
Europe finds itself divided by what is called the Iron Curtain, separating the Soviet camp from the Western camp.
The USSR monitors the 8500 km of this new political border,
with the main objective being preventing migration from East to West.
A zone of up to 5 km wide is forbidden to the population,
while on the western side there’s a strip about ten meters wide,
without constructions or vegetation, which is mined and monitored.
Finally, the border is closed by a barbed wire fence that can be electrified.
In Korea, the war rages between North Korea – supported by the communists –
and South Korea – defended by the Western camp.
In 1953, a cease-fire is signed,
and a demilitarized zone 250 km long and 4 km wide becomes the new border between the two countries.
The central zone is completely empty, while the extremities are mined and closed off by electric and barbed wire fences.
The DMZ is constantly guarded by more than one million soldiers,
making it the most militarized zone in the world.
In Germany, Berlin, which is divided in two,
remains an easy passage point for those who want to migrate from the Soviet camp to the Western camp.
To put an end to this migration, on the night of August 12th to 13th, 1961,
the Soviets begin the construction of a brick wall
topped with barbed wire along the 43 km of the border between East and West Berlin.
This wall, which is under high surveillance, will be progressively improved,
to finally be composed of concrete panels over 3 meters high.
In 1969 in Belfast, violent clashes take place between Catholics,
who are victims of discrimination, and protestants.
Little by little, walls are installed throughout the city to separate Catholic and Protestant neighborhoods.
Called “walls of peace”, they can be metal fences, or brick or concrete walls that can measure up to 7 meters high.
In the Mediterranean Sea, Cyprus, which has been independent since 1960,
is torn by violence between the Greek and Turkish communities.
In 1974, Greece, which dreams of annexing Cyprus, supports a coup d'état.
In response, Turkey invades the north of the island.
After a ceasefire, a buffer zone, called the Green Line, is created to divide the island in two,
including the capital Nicosia.
This 180 km long zone is under the supervision of the United Nations.
In Africa, after Spanish withdrawal from Western Sahara,
the independence of the Sahrawi Arab Democratic Republic is proclaimed by the Polisario Front.
But the territory is also claimed by Morocco and Mauritania.
In 1979, after a coup in Mauritania, a peace agreement is signed with the Polisario Front,
and the country abandons its territorial claims.
Morocco then begins the annexation of Western Sahara.
Over 7 years, the country builds 6 walls that allow it to control 80% of the territory.
2,700 km long, the wall is mainly made of sand and stones to a height of 3 meters.
The area is constantly under military surveillance, including with radar.
In Berlin, on November 9th, 1989, after weeks of demonstrations,
the Berlin Wall is torn down, marking the beginning of the fall of the Soviet bloc and the USSR.
Despite the end of the Cold War,
the construction of new walls explodes in the world at the beginning of the 21st century.
In Asia, India and Pakistan are fighting for control of Kashmir since 1947.
The region is divided between the two countries, with some little parts under Chinese control.
In 2004, India finalizes the construction of 550 km of walls on its part,
mainly barbed wire fences intended to prevent infiltration of Pakistani separatists onto its territory.
At the same time, Israel, after the second intifada,
builds a 730 km long wall in the West Bank to prevent attacks on its territory.
But during its construction, Israel takes the opportunity to encroach on the Palestinian territories.
This wall is mainly made of barbed wire fences that are bordered by a road that allows the passage of patrols.
Where it goes through towns, it is composed of concrete slabs up to 8 meters high.
In the Gaza Strip, after Hamas takes power,
Israel and Egypt begin building walls all around the enclave to block migration, smuggling, and attacks.
The wall built by Israel goes several dozen meters deep into the ground to prevent the construction of tunnels.
The Arab Spring, tensions in the Horn of Africa, the war against ISIS, the instability of Afghanistan
are all causing huge waves of migration to Europe.
In 2015, more than 1 million migrants enter the old continent.
In response, many European states are trying to block this migration by building walls and barbed wire barriers,
including within the Schengen area itself.
In North America, the border between the United States and Mexico
is by far the most crossed border in the world, with approximately 350 million legal crossings per year.
In 2016, during the presidential campaign,
Donald Trump promises to build 1,600 km of walls to combat illegal immigration, and drug and gun smuggling.
5.5 m high, he promises it will be entirely financed by Mexico.
But despite his election, the project is obstructed on multiple fronts,
and in 2021, at the end of his mandate, only 83 km of new walls have been built,
with an additional 650 km of existing walls being upgraded.
In addition to all of this nation state wall building,
more and more walls are being built all over the world to isolate rich neighborhoods from poor ones.
Today, new types of walls are appearing in certain coastal areas or along rivers
to protect against the forces of nature.
In Japan, after the 2011 tsunami,
the country is now finalizing the construction of 430 km of concrete anti-tsunami walls,
very thick at the base, and sometimes up to fifteen meters high.
In New York, on the island of Manhattan,
a concrete wall up to 8 meters high and 18 meters deep is being built to prevent future floods
that are likely to be increasingly frequent due to rising sea levels.