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 known the world over as the Great Wall. These walls have an average height of 7.8 meters (25.6 feet), and the highest section reaches 14 meters (45.9 feet). Unlike normal walls, most sections of the Great Wall 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
Earth walls are the earliest walls of the Chinese Great Wall. As the name suggests, the walls were made of earth. According to the different ways of construction, earth walls can be divided into three kinds: pure earth walls, earth walls with wooden frames, and earth walls with adobe. Earth walls were mainly found in the northwest of China, especially the walls with wooden frames which were the earliest and most widely used form of construction. The earth walls 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. These Earth walls were mainly built before the Sui Dynasty (581 - 618), especially during the Han Dynasty (206 BC - 220 AD). Famous walls are Yumenguan Pass and Dunhuang Han Great Wall. The Earth walls with adobe were built of adobe and plastered with mud. The walls were much easier to construct than the walls with wooden frames. Famous wall with adobe is Jiayuguan Great Wall.
Stone Walls
hese 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 stone walls are Laolongtou Great Wall and the wall near Badaling Great Wall.
Brick Walls
From the Tang Dynasty (618 - 907), bricks were used in the Great Wall's construction. Walls of that time were filled with earth and covered with bricks. 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 of Great Wall. 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 remain the best-preserved parts of the wall.
