In c. 220 B.C., under Qin Shi Huang, sections of earlier fortifications were joined together to form a united defence system against invasions from the north. Construction continued up to the Ming dynasty (1368-1644), when the Great Wall became the world's largest military structure. Its historic and strategic importance is matched ony by its architectural significance. UNESCO World Heritage Site since 1987.
Huang, thanks a bunch for the great postcard and lovely stamps!