The city wall of Beijing was a fortification built around 1435. It was 23.5 km long. The thickness at ground level was 20m and the top 12m. The wall was 15m high, and it had nine gates. This wall stood for nearly 530 years, but in 1965 it was removed to give way to 2nd Ring Road and the loop line subway of Beijing. Only in the southeast, just south of Beijing Railway Station, stands one part of the wall. Beijing was the capital city of the last three dynasties as well as two northern dynasties in the history of China, as such, Beijing is often referred to as an "ancient capital of Five dynasties" (五朝古都)...