Great Wall of China Great Wall of China The Great Wall of China is a series of fortifications made of stone, brick, tamped earth, wood, and other materials, generally built along an east-to-west line across the historical northern borders of China to protect the Chinese states and empires against the raids and invasions of the various nomadic groups of the Eurasian Steppe with an eye to expansion. Several walls were being built as early as the 7th century BC; these, later joined together and made bigger and stronger, are collectively referred to as the Great Wall. Especially famous is the wall built in 220–206
Underground Great Wall of China Underground Great Wall of China The Underground Great Wall of China ( ) is the informal name for the vast system of tunnels China uses to store and transport mobile intercontinental ballistic missiles. Due to the great secrecy surrounding the tunnels, not much information about them is publicly available; however, it is believed that the tunnels allow for mobile ICBMs to be shuttled around to different silos, and possibly stored in reinforced underground bunkers. This greatly enhances the ICBM's chance of survival in a direct nuclear strike, which enables their use in a second strike unlike ICBMs based in static