The British authorities have started building a 1km wall in the northern French port city of Calais to keep refugees and migrants from getting onto trucks heading for Britain.
The government is spending £1.9 million (S$3.3 million) on the 4m-high barrier, an extension of an existing barbed wire fence which runs on both sides of the road near the notorious "Jungle" refugee camp, which houses over 10,000 displaced people.
More than 84,000 migrants have been caught trying to enter Britain illegally since last year from ports such as Calais. "People are still getting through," said Britain's new immigration minister Robert Goodwill when he announced the plan in August. "We have done the fences. Now we are doing the wall."
Number of fortified walls built since the end of World War II.
Number of those walls built between 2000 and 2014
DIVIDED, WE WILL FALL
The world is more interconnected than ever before... Building walls won't change that… If the past two decades have taught us anything, it's that the biggest challenges we face cannot be solved in isolation.
U.S. PRESIDENT BARACK OBAMA, in response to US presidential nominee Donald Trump's plan to build a wall between the US and Mexico
Even as world leaders espouse the virtues and importance of a globalised, interconnected and borderless world, they are at the same time erecting physical barriers to protect their borders and keep unwanted people out.
Not since the fall of the Berlin Wall in 1989 have barriers been going up with such fervour. In the 20 years since the end of the Cold War, the number of walls has more than tripled, said geography professor Elisabeth Vallet, of the University of Quebec in Canada.
According to political scientists Ron Hassner and Jason Wittenberg, from the University of California, Berkeley, of the 51 fortified boundaries constructed since the end of World War II, about half were built between 2000 and 2014.
US Republican presidential nominee Donald Trump stirred controversy when he mooted the idea of a wall that would keep out illegal immigrants from Mexico.
In Europe, walls are emerging along borders in response to the migrant crisis that has plagued the continent. Hungary is fortifying its existing barrier to prevent refugees from crossing its border, en route to western Europe. The current razor wire fence already runs the entire length of its borders with Serbia and Croatia.
Norway, too, is putting up a steel fence at its remote arctic border with Russia that will be completed by winter. Last year, 5,500 migrants, mostly from Syria, crossed this border.
Turkey, Saudi Arabia, Morocco, Spain, Ukraine and Kenya have also all built or are building anti-immigrant, anti-terrorist barriers.
In Asia, China has extended its barbed wire fence separating North Korea to keep defectors out, while India is erecting a barricade at the Myanmar border to prevent drug smuggling, and an anti-migrant fortification with Bangladesh. Malaysia and Thailand in August also agreed to fence their borders to stop smuggling and trafficking activities that have gone on for decades.
Walls have traditionally been used to keep enemies out. The Roman Empire constructed limes, a line of border fortifications, walls and forts to protect it from invaders.
The Great Wall of China, running over 21,000km, was built to keep the Chinese states safe from raids by nomadic tribes from Inner Asia.
Today, immigration, terrorism, and drug and people trafficking have largely contributed to the revival of walls. Security fears, stoked by the 9/11 terrorist attacks in the US, and a backlash against globalisation have compelled countries to bolster their defences.
"What initially could be interpreted as a tightening of security spurred by 9/11 proved to be a ratchet effect produced by the reaction against fast-paced globalisation, which has not been wholeheartedly embraced by many members of the international community," wrote Professor Vallet in her book Borders, Fences And Walls: State Of Insecurity?
Experts say there is nothing to suggest that such border controls are effective. Professors Hassner and Wittenberg argue that walls must be complemented by broader control measures, such as surveillance, which also has to be on both sides of the barrier.
Amnesty International UK's refugee and migrant rights programme director Steve Symonds believes a security barrier will only cause more harm. "A wall will simply further empower smugglers by forcing people to take even greater risks to get across the channel," he said.
A reported 13 refugees and migrants, including three children, have died this year trying to get onto trucks in Calais bound for Britain.
"The world is more interconnected than ever before, and it's becoming more connected every day," said US President Barack Obama in response to Mr Trump's plan to build a wall to keep out "drugs, crime and rapists".
"Building walls won't change that… If the past two decades have taught us anything, it's that the biggest challenges we face cannot be solved in isolation."
Walls are being built all over the world at a rate not seen since the end of the Cold War.
A 4m-high wall to block "jungle" refugee camp migrants from stowing away on trucks bound for Britain. Paid for by the British government, the wall is an extension of an existing barbed-wire fence that is already flanking the road.
A 500m razor-wire fence was built along Hungary's border with Serbia and Croatia last year, after over 400,000 refugees crossed over to get to other parts of Europe. Plans are under way to build a "massive defence system next to the existing line of defence", said Hungarian Prime Minister Viktor Orban.
Ukraine will begin "Project Wall", a barrier on its easternmost border with Russia to fortify its porous, nearly 2,000km frontier. Announced in 2014, the ambitious project aims to prevent Russian military intervention in Ukraine.
The "Berm", a sand wall in Western Sahara, runs for about 2,700km in harsh, uninhabited territory.
It is meant to keep out Sahrawi rebels, who want to end Moroccan presence in the Western Sahara.
Morocco erected the wall in 1975, shortly after it occupied Western Sahara.
Also known as the "Apartheid Wall", the Israeli-West Bank barrier runs for 700km. Israel says it is an anti-terrorist measure but Palestinians say it is aimed at racial segregation. Built in 2000, the wall has been effective in reducing the number of suicide bombings carried out from the West Bank, says Israel.
The wall resulted in reduced freedoms, loss of land and difficulty in accessing public services and water for the Palestinians.
Turkey is sealing its border with Syria with a 900km wall to stop the influx of Syrian refugees fleeing the war-torn country and also Islamic State in Iraq and Syria (ISIS) fighters. It has already built 200km of the wall and will finish the rest within five months.
Saudi Arabia began planning for a barrier in 2006 after sectarian violence broke out in Iraq.
But it was not until 2014, when the ISIS threat intensified, that it started constructing the wall, which will be about 900km, and run along its isolated northern desert border.
A combination of a multilayered fence and ditch, the border will also be fortified with 78 watchtowers, night-vision and radar cameras, and eight command centres.