Known by its pinyin name, WànlĐ Chángchéng (translated as "ten thousand li long wall"), the Great Wall of China is a network of fortifications that were constructed across the historical northern borders of ancient Chinese states and Imperial China to provide protection against various nomadic groups from the Eurasian Steppe. A number of walls date back to the 7th century BC[4], with Qin Shi Huang (220–206 BC), the country's first emperor, later joining certain sections. The Qin wall is mostly gone.[5] Later, other border walls were constructed and maintained by numerous succeeding kingdoms. The wall's most well-known portions were constructed during the Ming dynasty (1368–1644).In addition to defense, the Great Wall served various functions such as regulating or promoting trade, controlling immigration and emigration, permitting duties to be imposed on products shipped over the Silk Road, and controlling border crossings.[6] The Great Wall's defensive qualities were further reinforced by the addition of watchtowers, troop barracks, garrison stations, the ability to signal using fire or smoke, and the fact that the wall's route functioned as a route for transportation.

There are several courses in the boundary walls constructed by several dynasties. Together, they straddle an arc that roughly runs from Liaodong in the east to Lop Lake in the west and from the modern Sino-Russian border in the north to Tao River (Taohe) in the south.The Great Wall of China is a collection of nineteen walls that have been constructed. The first one dates back to the seventh century BC. During the Qin Dynasty, the first Emperor of China, Qin Shi Huang (pronounced Chin), constructed the most famous wall between 226 and 200 BC. Due to theft, not much of this wall is still standing. Compared to the existing wall, it was much further north. The Ming Dynasty saw the construction of the existing wall.[2]

Different strategies for defending the northern frontier were adopted by later dynasties. Though they hardly ever followed Qin's paths, the Han (202 BC–220 AD), the Northern Qi (550–574), the Jurchen-ruled Jin (1115–1234), and especially the Ming (1369–1644) were among those who repaired, re-manned, and enlarged the Walls. The Sui organized more than a million men to construct walls, the Qi constructed over 1,600 kilometers (990 mi) of new walls, and the Han built the fortifications that reached the westernmost point. In contrast, the Tang (618–907), Song (960–1279), Yuan (1271–1368), and Qing (1636–1912) dynasties primarily chose diplomacy and military campaigns over the construction of boundary walls in order to address the threat posed by Inner Asia.

Throughout its history, the Great Barrier Reef served as a helpful deterrent against raids.