History of great wall china

 The Great Wall of China is an ancient wall in China. The wall is made of cement, rocks, bricks, and dirt. It was finished in 1878^[1] and it was meant to protect the north of the empire of China from enemy attacks. It is the longest structure humans have ever built. It is about 21,196 kilometers long, 9.1 metres (30 feet) wide and 15 metres high. The earlier sections on the wall are made of compacted dirt and stone. Later in the Ming Dynasty they used bricks. There are 7,000 watch towers, block houses for soldiers and beacons to send smoke signals.Later dynasties adopted different policies towards northern frontier defense. The Han (202 BC – 220 AD), the Northern Qi (550–574), the Jurchen-ruled Jin (1115-1234), and particularly the Ming (1369–1644) were among those that rebuilt, re-manned, and expanded the Walls, although they rarely followed Qin's routes. The Han extended the fortifications furthest to the west, the Qi built about 1,600 kilometres (990 mi) of new walls, while the Sui mobilised over a million men in their wall-building efforts. Conversely, the Tang (618–907), the Song (960–1279), the Yuan (1271–1368), and the Qing (1636–1912) mostly did not build frontier walls, instead opting for other solutions to the Inner Asian threat like military campaigning and diplomacy.

Although a useful deterrent against raids, at several points throughout its history the Great Wall failed to stop enemies, including in 1644 when the Qing troops marched through the gates of the Shanhai Pass and replaced the most ardent of the wall-building dynasties, the Ming, as rulers of China proper.

The Great Wall of China visible today largely dates from the Ming dynasty, as they rebuilt much of the wall in stone and brick, often extending its line through challenging terrain.^[2] Some sections remain in relatively good condition or have been renovated, while others have been damaged or destroyed for ideological reasons,^[3] deconstructed for their building materials,^[3] or lost due to the ravages of time.^[4] For long an object of fascination for foreigners, the wall is now a revered national symbol and a popular tourist destination.^[5]