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The world's most controversial border-control projects

West Berliners crowd in front of the Berlin Wall early 11 November 1989 as they watch East German border guards demolishing a section of the wall in order to open a new crossing point between East and West Berlin, near the Potsdamer Square.

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Walls of worry

Since the ancient Romans erected their empire-defining stone walls, governments have continually built walls to keep out invaders, crusaders, foreigners — and to control their own populations.

During the Cold War, the Berlin Wall became the most notorious wall in history designed to keep citizens inside its boundaries. Yet the most iconic photos of the Berlin Wall are from the eve of its fall: November 9, 1989, when East Germans defied their captors and breached the wall.

Do physical walls work as instruments of border control in the 21st century? Do such physical deterrents offer a humane solution to the global issue of migration?

Since the Berlin Wall fell in 1989, more than 40 countries around the world have erected border walls. From Israel's West Bank Wall to new walls (mostly fences) currently being erected in Eastern Europe, these are some of the most contested border-control projects in the world.

By Sarah Chandler, special to CNBC.com
Posted 09 October 2015

Gerard Malie | AFP | Getty Images