Walls Forming the Great Wall

As it traverses thousands of miles across northern China, the Great Wall is mainly composed of undulating sections of wall that play a major role in the overall defensive system. They have an average height of 7.8 meters (25.6 feet), and the highest section reaches 14 meters (45.9 feet). Unlike normal ones, most sections are wide on the top (averaging to 5.8 meters (6.3 yard)), which allowed four horses or two carriages to stand abreast.

Due to the different topographical locations and construction time line, walls vary in both their structure and materials, and can be categorized as follows:

 Earth Walls 
They are the earliest ones. As the name suggests, they were made of earth. According to the different ways of construction, they can be divided into three kinds: pure earth, those with wooden frames, and those with adobe. They were mainly found in the northwest of China, especially those with wooden frames which were the earliest and most widely used form of construction. Those with wooden frames were filled with earth and grey gravel. Some sections in the northwest of China were built of layers of earth and sands with branches of red willow or reed. They were mainly built before the Sui Dynasty (581 - 618), especially during the Han Dynasty (206 BC - 220 AD). Famous sections are Yumenguan Pass and Dunhuang Han Great Wall. Those with adobe were built of adobe and plastered with mud. They were much easier to construct than those with wooden frames. Famous sections is Jiayuguan. 

 Stone Walls 
These are mostly found in mountainous areas, as stones and rocks were readily available on site. From the Ming Dynasty (1368 - 1644) raw stones were processed into rectangular shapes that were used for the outer layers with rough stones and rocks used as infill between them. Famous sections are Laolongtou and some sections near Badaling.

 Brick Walls
Bricks were started be used from the Tang Dynasty (618 - 907). However, bricks were too expensive to be widely used in the Tang and Song (960 - 1279) Dynasties. Later in the Ming Dynasty, bricks were cheaply mass-produced and became the major material. Most of the brick walls dating from the Ming Dynasty have outer layers of brick with stone and rubble infill. Only few were completely formed with bricks. As brick construction was far firmer and solid, those sections are well-preserved.