Borders serve as the physical display of a nation's sovereignty, identifying the territory under its control. Even the smallest international borders are usually marked by strict security and border control. For example the frontier between North Korea and South Korea the demilitarized zone( DMZ) stretches for about 155 miles, marked by high fences and barbed wire.... The bridge has a single-line railway track between two traffic lanes and pavements for pedestrians. During the building of the K