Course:EOSC311/2020/How it was Built: The Great Wall of China

The Great Wall of China during autumn

Introduction

The Great Wall of China is the longest man made structure in the world and certain the largest man made structure in China. Interestingly, the Great Wall was not constructed at once, it is the product of many structures built by different Chinese Dynasties that were merged together. There is evidence that the beginnings of the Great Wall started during the Warring States Period which was dated 770-221 BC. During the Warring States, the Chu, Qi, Wei, Yan, Zhao, Qin, and Han were the seven rival states in a power struggle. They each constructed their own wall for defensive against each other and also nomadic tribes attacking occasionally from the north. Fast forward to 221 BC which was the ended of the Warring States Period and Qin Shihuang took the throne. Qin Shihuang, the first Chinese Emperor was able to take the Qin to victory and defeated the other states and under his command, he unified all the Chinese states under a feudal system and this was the start of the Qin Dynasty. As the number of attacks from Mongols from the north increased, under the command of Qin Shihuang, the various parts of walls that were erected by previous states were to be linked together to form one massive wall, which will be part of the Great Wall of China we see today. Qin Shihuang was the mastermind behind the Great Wall of China, but he died shortly after in 210 BC which meant he wasn't able to see much of the wall being built. The remainder of the Wall was built in the Han Dynasty (206 BC-220 AD) and the Ming Dynasty (1368-1644 AD). The Han were more focused on repair the original Qin wall while the Ming built the vast majority of the Wall that we see today. In the end, the total span of the finished Great Wall of China was over 13,000 miles long and took 22 centuries to finish. Various other Dynasties were also involved in the construction of the Wall, but the work they did were minute in comparison or the the Qin, Han, and Ming Dynasties. The construction of the Great Wall ended with the fall of the Ming Dynasty which was overtaken by the Qing Dynasty in 1644 AD.

Statement of connection and why you chose it

I decided to pick the Great Wall of China as my project because the major I'm in is Asian Area Studies. In the various Asian studies courses involving Chinese history that I have taken over the course of four years, they would give a little introduction of the Great Wall and talk about how Emperor Qin Shihuang commissioned the Wall to be built, but they never seemed to go into detail. I saw this as a perfect opportunity to go more in dept about the history and purpose behind the construction of the Great Wall of China and to also study the processes and material used to created the Great Wall. As the majority of the Great Wall is constructed out of rocks with a mix of other materials such as soil and decayed plants, this means I was able to link the Great Wall to geology. Specifically I would like to figure out exactly which types of rocks were used for the construction of the Wall and also to study the terrain in which the Wall passed through. In addition, the Chinese incorporated bodies of water such as rivers as natural defence barriers that were part of the Great Wall which means this is related to the study of sedimentology.

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Map of China that shows the location and span of the Great Wall of China

With the Great Wall of China spanning over 13,000 miles and with an average height and width of 7 to 8 meters, it is not an easy task, not even if we were to reconstruct that same wall with our advanced modern day technology. The construction of the Great Wall demanded a tremendous work force that consisted of millions of workers which included soldiers, common people, slaves, prisoners, and sometimes even women if the local town didn't have enough men to work. In the ancient times, there were no special technology that the workers could utilize when constructing the Wall. They relied purely on man power and basic hand tools. Animals such as horses, oxen, camels, goats and donkeys were also utilized to transport building material through steep mountainous and dry desert terrains. Some methods that the workers used to carry and transport material included hand bombing, baskets, shoulder poles, rolling them on logs and spreading into a long line and passing the material onto one another to avoid walking up steep inclines.

Map of China that shows the different biomes by region

The material used to construct the Wall was basically whatever could be found locally to where the Wall was being built at the time. There were four main types of material used on the Wall: packed earth, bricks, stone, and a mixed of stone and brick. Usually at higher elevations, stones were mined from mountains and incorporated into the Wall or they were first crushed into bricks before being used to construct the Wall. On lower elevation surfaces such as plains, the main method for constructing the Wall was just to pack down earth/dirt to form the Wall. There were four specific rock types that were used and they include granite (igneous rock), marble (metamorphic rock), limestone (sedimentary rock), and shale (sedimentary rock). China's soil is unlike the soil found in North America, the soil in China is rich in clay, also known as loess, which was extensively used in the construction of the Wall. Vertical wooden structures, similar to forms used in modern day concrete pouring technique, were put up and then loess was poured into it and compacted. This technique was surprising extremely stable and has held up well to the weather conditions. The Wall passed through many different terrains including deserts. As the workers used materials local to them to build the wall, there wasn't much available to them except for sand, gravel, and native desert plants. The workers were able to create a blend the gravel with decayed plant material while separating them into layers with branches, this was extremely effective and til this day the portion of the Wall that was built using this technique still stands. During the Ming Dynasty there was a new way of building the Wall and that was to use bricks instead of raw material. Rocks and stones were crushed to form bricks which was then fired in a kiln which was heated in excess of 1000 degrees Celsius. These bricks were fired for 7 days before being used to ensure that all the moisture within in them were gone. The bricks that were created using this method was much stronger than the other methods previously and was used to build a majority of the Wall. Even though these bricks were extremely durable, water as the strongest erosion agent, has taken a toll on the Wall over the centuries and the Wall has been repaired many times during the course of its lifetime.

Igneous Rock

Igneous rock is formed when magma or lava is cooled and then solidified. The grain size on igneous rock are determined by whether it was cooled faster as extrusive rock or cooled slower as intrusive rock. Extrusive igneous rocks cool faster on the surface of Earth, resulting in finer grains. Granite is considered intrusive igneous rock and contains medium to coarse grains because it cooled slower and that give it the appearance of salt and pepper grains. This rock is usually found in steep mountain slopes and is erosion resistant, which means granite is likely to be used to build the steep mountainous regions that the Wall passes through.

Metamorphic Rock

Metamorphic rock is formed when sedimentary rocks are put under extremely heat and pressure. These types of rocks are typically found in mountainous regions where rocks undergo extreme pressures of rocks being compressed by mountains. The metamorphic rock used during the construction of the Wall was marble and like the igneous rocks used, was erosion resistance and has held up to the environment over the years. Metamorphic rock sections of the Wall would also be found in mountainous regions in China like the igneous rock sections.

Sedimentary Rock

Sedimentary rocks are different from other types of rocks. They are made up of particles that are cemented together through compaction. Sedimentary rock is weaker than other rocks as it has not undergone extreme pressures like metamorphic rock and igneous rocks. Limestone and shales were the sedimentary rocks used for construction of the Wall. The sections of the Wall that were constructed out of sedimentary rock were heavily damaged due to erosion hence they have been repaired many times.

The Great Wall of China was designed very carefully, therefore when natural barriers such as mountain cliffs or rivers could be utilized to save work, they were incorporated into the Wall. These natural barriers made up 25% of the Wall which saved a lot of work for such a humongous project. The Yellow River, which is China's longest river, was largely incorporated into the Great Wall. Other rivers that were included to the Wall were Liao River and Yi River, they were much shorter and thinner, but the purposed they served were the same.

There are four distinct ecosystems that the Great Wall passes through: desert, temperate mixed forest, temperate deciduous forest, and steppes/grasslands. The materials used throughout these different ecosystems were all locally acquired like stated before. Desert ecosystems used plant based materials and gravel, forest regions used stones acquired from steep mountains slopes and grasslands made use of soil and bricks.

There were three distinct structures that were used throughout the construction of the Wall: the walls, military passes, and beacon towers. The walls are very self-explanatory, their purpose was to defend and made up a vast majority of the Wall. The walls averaged around 7-8 meters tall and where workers were able to utilize steep mountain slopes, the walls would be shorter. The walls started wide at the bottom and got a little more narrow on while going up for added stability. There were many accommodations built into the wall such as watchtowers and living quarters. The walls consisted of multiple levels and on the upper levels were where the watchtowers and armouries were built. The lower level accommodated the soldiers that were patrolling that section of the Wall. There were also defence towers built into the wall that held weaponries such as gun powder and other weapons. The next important structure that was used throughout the Great Wall were military passes. These passes were built as entry and exit points to major towns and cities during that time. The military passes were essentially heavily guarded arches in the walls that allowed traffic to come in or go out. Each pass would compose of double wooden doors that could be locked with bolts from the inside of the Wall. At each pass were also ramps that allowed movement of horses and soldiers to move up and down the Wall. The main functions of these military passes were to allow deployment of garrisons, but later on as trade increased in China, these military passes served as entry points into major cities. Lastly beacon towers are another structure that was crucial to the effectiveness of the Great Wall. Beacon towers were built in hilltops that has limitless visibility and spread out along the Wall. The purpose of these beacon towers were to transmit signals such as invasions to other parts of the Wall so reinforcements could be arranged if needed. During the day time smoke signals were used and during nighttime fires were lit. At the time, these beacon towers were extremely efficient as they were able to transport signals over 500km in only a few hours.

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Conclusion / Your Evaluation of the Connections

I believe the Great Wall of China provides an excellent connection to geology. Even though the Great Wall of China doesn't touch upon all the subjects included within the scope of geology, it touches upon the study of rocks and rivers, petrology and sedimentology. As the Great Wall of China was constructed mostly with rocks and other natural materials, it is interesting to see how the Chinese workers were able to rocks and soil combined with ancient methods to create one of the most impressive structures that exist in this world. Even though the Great Wall was built with some of the most durable and erosion resistant rocks, most of the Wall has been repaired multiple times due to water and other erosion agents. The Great Wall of China that is available to the public to see has mostly been renovated or restored during modern day and some parts of the Wall has been eroded so badly that repairs couldn't even help it. The Great Wall has held up against many invasions and wars, but it could not hold up against the strongest erosion agent, water.

References

This Earth Science resource was created by Course:EOSC311.