Donald Trump built his presidential campaign around the concept.
His rallying cry, for which he is now well known, has long been: “We’re going to build a wall."
The American president is calling for a physical barrier all along the 1,954-mile border between Mexico and the US, in a controversial plan to prevent people crossing the border illegally.
But with all this talk about the border wall in the US, it got us thinking – do walls work?
And what could President Trump learn from military walls?
Documentary-maker Simon Thornton - producer of Intel, a Science, Technology, Engineering and Mathematics (STEM)-focused BFBS video series - explored how walls have been used in defence and spoke to some of the world’s military wall experts to find out if walls work.
Walls Along A Border Are Nothing New
Hadrian’s Wall, for instance, built by the Romans to keep out the Scots, acted as the north-west frontier of the Roman empire for almost 300 years and was built by the Roman army on the orders of emperor Hadrian sometime after AD 122.
That is just one example of the many historically renowned defensive barriers the world over, including what is known as the longest defensive wall in the world, the Great Wall of China.
How Are Modern Military Walls Designed?
There is one design element that all modern military walls have in common, however – they all have more than just one wall.
In Intel, Simon tests the theory as he speaks to military experts, including the team at defensive barrier specialists Hesco, which engineers blockades and wall systems in military establishments the world over, including hostile environments such as Afghanistan.
The HESCO MIL is a modern version of a gabion system – a gabion being a basket or container filled with earth, stones, or other material that has been used in fortifications dating back to Roman times.
Mike Pickup, engineering director at Hesco, said that the concept of a Hesco barrier was easy to transport, it folds flat and is relatively light.
He added: “Once you fill it, and you can normally fill it with almost any fill material that can find, then the performance of the product is outstanding.
“To coin a phrase, it was a real game-changer for a lot of the militaries.
“There is a quote by some general saying that it was the biggest evolution in force protection for the last 500 years. It’s something like that.
“Gabions are not a new idea. I mean the Romans used them – they had wicker baskets that they filled in with dirt, so the concept is very old.”
He said that the company had taken it to the next level by creating the 21st century version of that concept.
Intel has explored how this invention changed the way modern armies go to war.
In the film, Simon said: “It might seem like a relatively simple design, but before Hesco, only a few decades ago, soldiers would have to build walls out of sandbags.”
Ben Jenkins, Hesco technical manager, explained how Hesco was developed about about 30 years ago.
He said that the Hesco Bastion barrier system was invented and designed by former coal miner James ‘Jimi’ Heselden.
Heselden used his redundancy money from the wave of job losses to hit the mining industry in the 1980s on setting up a sandblasting business.
However, it was during this time, as he experimented in his workshop with engineering and construction, that he also faced losing his cliff-side home to coastal erosion.
Mr Jenkins said: “Jimi had a property on the east coast and it was very close to the cliff face which was eroding away.
“He wanted a product that he could install rapidly and effectively and that it would stop further corrosion to the coast.
“He developed the lined gabion unit, constructed it on the cliff face, filled it with cement and then, as a result, that saved his property.”
He went on to patent his collapsible wire mesh and fabric container as a commercial product, initially designing it for use in flood management, to limit erosion.
However, the system soon found favour with the military as it became apparent the Hesco Bastion system provided effective blast walls and barriers which could be quickly constructed. Simon said:
“So this invention that started in someone’s garage has really become a whole system that changes the way modern militaries can go to war.”
He said the barriers can be a simple walls constructed by soldiers or a whole barrier can be unloaded at speed out of an ISO container.
“There’s a whole range of products that use this simple structure, to make bigger, more useful things like an accommodation block, or weapons stores, or anything like that.
“It’s allowed for new tactics where forward operating bases can be constructed overnight.”
An Effective Barrier Is Always More Than One Wall
Mr Jenkins said: “Usually, to have an effective wall, it needs to be part of suite of a solution to basically delay or deter an attacker.
“So we would have a solid, earth-filled wall, then usually we would have some form of stand-off which is a distance between the wall and another product, for instance a fence.
“So a potential attacker has to break through many layers of a defence even before he gets to the wall itself.
“The important thing is that you react in the time it takes a potential attacker to get through that system.”
Intel explores the many factors that need to be considered in creating an effective barrier – that includes more than the length and breadth of the perimeter.
It also needs to take into consideration what kind of assault the barrier might face – would that include vehicles for explosives for instance.
Mr Pickup said: “One of the things that you have to do, even though you’ve got something to physically stop a bomb, or a bullet, a car or a person – you’ve got to physically watch that barrier.
“Because if you don’t watch it, people will get through it, over it or around it, whatever.
“So you have to watch whatever system you have deployed.”
On military operations, such layers of defence are everywhere.
Hesco’s advice on layers of defence, and keeping watch, is not a new concept.
During the Cold War, these defensive techniques were used all across the inner Germany border, between the German Democratic Republic and the Federal Republic of Germany from 1949 to 1990, of which the infamous Berlin Wall was a part.
It is the most recent example of a border wall that would be anywhere near the size of a wall separating Mexico and the United States.
The Iron Curtain formed the imaginary boundary dividing Europe into two separate areas from the end of the Second World War in 1945 until the end of the Cold War in 1991.
It cut Europe and Germany in half and was one of the most militarised and highly defended borders the world had ever seen.
Migration form the East to the West of the Iron Curtain was a major problem for the Soviet Union – thousands of people leaving, didn’t look good for Communism.
In the five years following the Second World War, more than 15 million people left Soviet-occupied Eastern Europen countries to live in the West.
Immigration was effectively halted after 1950 when border defences were erected.
This border wasn’t built to keep people out, it was built to keep people in.
It worked – before the first walls and fences were erected, more than 200,000 people were leaving the German Democratic Republic every year.
When the barriers went up in 1961, that number fell dramatically, remaining at low numbers until the walls started to come down in 1989.
Unlike the proposal for President Trump’s wall, this border was not one obstruction – it was a series of multiple hurdles and walls to prevent people from crossing.
This included a road running the length of the border to allow a rapid response by border security guards, anti-vehicle barriers, and lines of fences – sometimes with automatically-firing weapons between the spaces, or mines, or dog patrols.
The Soviet Union continually added to the defences because some people were still managing to succeed in getting through the barriers.
Walls, fences and other barriers can work but they need a whole range of additional defences and surveillance.
As early as 122 AD, the Roman Empire was building barriers with this in mind – which is why all along Hadrian’s wall, there are forts to house the garrisons of soldiers needed to keep a wall of that length effective.
Similar constructs can already be seen along the Mexico – US border.
There are aerostats watching for migrants from the air, patrols of border guards using boats, trucks, seismic sensors, motion cameras.
Border guards train with the military to practice catching illegal migrants.
The border between Mexico and the US was already heavily guarded before President Trump took office.
In the late 1980s, the first walls and fences were being built using military surplus helicopter landing mats from Vietnam, but even with all that infrastructure, people were still making it across.
A wall could possibly bring down the numbers of illegal migrants crossing – walls have proved to be significant on military operations throughout history, but in modern defence, they are more effective when they make use of technology and a complex, layered system.
And, when it takes more than just a barrier to defence the average military base, defending 2,000 miles of border will present significant challenges.
What Is Happening With The Wall In America?
Trump says that a wall is needed to tackle illegal immigration into the US at the border – this was a signature promise of his 2016 election campaign.
There were about 650 miles of barrier along America’s southern border before he took office and this included about 354 miles of barriers to stop people crossing on foot and about 300 miles of fences aimed at preventing vehicles crossing.
Funding a border wall is a policy strongly opposed by Democrats in the country.
So far, reports suggest that no new wall has been built since Trump took office but that 51 miles of fencing had replaced barriers that had already existed.
However, the US Supreme Court has said that Trump can use £2.5 billion of Pentagon funds to build a section of wall on the southern border – a move that comes after the president declared the border issue a national emergency early in 2019.
That figure falls far short of the estimated $23bn cost of a barrier along the whole border line.
The decision to allow military funds to be diverted to the wall project has also angered many, not only Democrats but others from the military community.