BELFAST PEACE WALLS
Whether these urban barricades actually helped to keep the peace during the Troubles, or just created more distrust and division between Catholic and Protestant communities, is a topic of much debate. One thing's clear though: these temporary-looking, corrugated iron walls have got some staying power.
They've worked their way into both the city's landscape and the national imagination, and have even become actual attractions for so-called "conflict tourists". Yet while sectarian tensions are still a reality in parts of Belfast, signs of change are there, with bright artistic murals covering sections of the barricades, and gates allowing for greater movement and exchange between formerly divided communities.
US-MEXICO BORDER FENCE
Stretching hundreds of miles along the vast US-Mexico border, this is one formidable border defence. In places, it's claimed to be essential for preventing illegal immigration into the United States and as a defence in the War on Drugs. Yet, as its detractors have pointed out, it hasn't stopped people from crossing the border - it's just made it a lot more dangerous, with increased migrant deaths reported.
In some parts, the wall is 4.5 metres high and three fences thick. In others, it's a virtual fence, relying on cameras and sensors. On-going construction of yet more barricades along the Texan stretch of the border and the strengthening of existing sections of the fence means that this particular barrier doesn't look like it will be coming down anytime soon.
WEST BANK BARRIER
Made up of sections of concrete wall 8 metres high, as well as electrified fences, this hugely controversial barrier wall cuts through the most contested land in the world. Stretching for 420 miles along the West Bank dividing Israeli and Palestinian territory. It divides Jerusalem, a city which holds deep symbolic and religious significance for both groups, as well as cutting off villages from basic facilities in some places.
Many Israelis consider it essential for on-going security in the region and reducing terrorist attacks. However, in some places, deviations from the "Green Line" mapped out in the 1949 armistice between Israel and its neighbours means that the wall almost encircles Palestinian communities. Like the Berlin Wall, this barrier is as much a powerful symbol of the continuing territorial disputes as a necessary political barricade.
KASHMIR LINE OF CONTROL
Like the West Bank Barrier, this hotly-disputed division between India and Pakistan shows no sign of being resolved anytime soon. The Line of Control came into being after the 1947-8 war between the two countries, in which they fought for control of Kashmir territory.
Despite numerous attempts by India to have the current Line of Control permanently fixed as a border, Pakistan has always refused, since it believes that the largely Muslim Kashmir Valley, currently within Indian territory, should become part of Pakistan. This means that skirmishes along the dividing line are frequent - it's arguably the most dangerous border region in the world. In a dazzling show of security, India has installed so many floodlights along its border with Pakistan that it can be seen from space at night.
KOREAN DEMILITARIZED ZONE
In a buffer zone, stretching right across Korean peninsula and 2.5 miles wide, armed soldiers patrol in front of sombre checkpoints and Soviet-style buildings. The earth is spiked with landmines, soldiers patrol at all times, and huge speakers occasionally blare out announcements or eerie military music. The word "Demilitarized" is spectacularly inappropriate for this intensely militarized barrier dividing North and South Korea.
In fact, anyone trying to cross, unless with piles of security and official sanctions for rare diplomatic meetings, is likely to be shot dead. Yet even at this terrifying, massive barrier, tunnels through it have been discovered over several decades. It proves the point that no matter how big you build a wall, or how heavily you reinforce it, there will always be attempts to get over it, under it, through it, or around it.