GREAT WALL OF CHINA

The Great Wall of China (simplified Chinese: 长城; traditional Chinese: 長城; pinyin: Chángchéng; literally "long city/fortress") or (simplified Chinese: 万里长城; traditional Chinese: 萬里長城; pinyin: Wànlǐ Chángchéng; literally "The long wall of 10,000 Li (里)"[1]) is a series of stone and earthen fortifications in northern China, built, rebuilt, and maintained between the 5th century BC and the 16th century to protect the northern borders of the Chinese Empire from Xiongnu attacks during various successive dynasties. Since the 5th century BC, several walls have been built that were referred to as the Great Wall. One of the most famous is the wall built between 220–206 BC by the first Emperor of China, Qin Shi Huang. Little of that wall remains; it lay farther north than the current wall, which was built during the Ming Dynasty.[2]
The Great Wall stretches over approximately 6,400 km (4,000 miles)[3] from Shanhaiguan in the east to Lop Nur in the west, along an arc that roughly delineates the southern edge of Inner Mongolia, but stretches to over 6,700 km (4,160 miles) in total;[4] a more recent archaeological survey using advanced technologies points out that the entire Great Wall, with all of its branches, stretches for 8,851.8 km (5,500.3 mi).[5][6][7] At its peak, the Ming Wall was guarded by more than one million men.[8] It has been estimated that somewhere in the range of 2 to 3 million Chinese died as part of the centuries-long project of building the wall.

Before the use of bricks, the Great Wall was mainly built from Earth or Taipa, stones, and wood.
During the Ming Dynasty, however, bricks were heavily used in many areas of the wall, as were materials such as tiles, lime, and stone. The size and weight of the bricks made them easier to work with than earth and stone, so construction quickened. Additionally, bricks could bear more weight and endure better than rammed earth. Stone can hold under its own weight better than brick, but is more difficult to use. Consequently, stones cut in rectangular shapes were used for the foundation, inner and outer brims, and gateways of the wall. Battlements line the uppermost portion of the vast majority of the wall, with defensive gaps a little over 30 cm (one foot) tall, and about 23 cm (9 inches) wide.