"Human history has known many barrier and division lines and structures. One of the most famous is the Great Wall of China. I think that it is the only man-made structure visible from space. But why is it still standing after hundreds of years? Because it protected a nation, while the Berlin Wall divided one. That, of course, was its unnatural aspect. It was clear to me that in the modern world, it is impossible to confine a nation and have it remain confined."