First came the 7 ancient wonders, but once their glory faded, the world selected a new group of wonders that stand with unmatched engineering prowess. This is the Great Wall of China.
The Great Wall of China is the longest structure ever built, and it is at the forefront of the world’s greatest engineering achievements. When discussing the engineering and design of the great wall, it is necessary to specify the time period of construction because the entirety of the nearly 13,000-mile wall was built over the course of 2 millennia. Like most walls, it was built to keep invaders and attackers out, and in the case of the great wall, to keep Mongols from raiding north Chinese land.
In terms of structure, the wall stands 20 to 30 feet in height, depending on the section, and 25 feet in width. The stone structure tapers as you move up the wall from the base, where the walkway and railing only stretch 16 feet wide in most sections. Designers of the historic site wanted much more than just a stone wall, rather they built 25,000 towers, castles, and other fortresses into the wall spaced at somewhat even intervals. There are also large towers every 11 miles to signal attacks to other areas of the wall. It was a defensive stronghold, one of the largest ever built, however, despite rumors, it cannot be seen from space.
Being such a large structure, the designers used earth and other local materials to fill the base. The stone that is seen on the exterior can essentially be thought of as a retaining wall. The ground was leveled and heavy stone slabs were placed on the footprint. Workers built the wall in successive layers, adding the stone exterior wall then backfilling that space with dirt and earth. This construction would have made the wall very resistive to attacks of impact at the time. Instead of using large stones dragged into place by workers, engineers opted for the much easier brick and mortar construction for exterior walls. There were kilns built onsite and teams of workers that would have spent their days molding and firing bricks. Given the earthen interior, this brick and mortar construction was sufficient for the defensive needs of the time.
Materials used in the construction, while the processes stayed the same, varied highly during different eras of building. Rammed earth was always used for the interior, but while bricks were used mainly during the Ming construction period, other sections include quarried rock and stone. Even up to modern standards, the stone, bricks, and mortar used in the construction were very strong.
Construction began as far back as the 7th century B.C., but the majority of the work was done in the Ming Dynasty between the 13th and 17th Centuries A.D. For the entirety of the wall’s history, it served its necessary purpose. The Northern Chinese kingdom did eventually fall to attackers, but due to government instability rather than the wall’s shortcomings.
Digging deeper into the intricate defensive engineering that was taken into account in the wall’s design, let’s examine two different fortification structures: Passes and Signal towers. Passes would have been the larger fortified areas of the wall structure. They would not have only been part of the wall structure, but they would have existed as forts of their own. Areas for horses and soldiers were laid out inside, and there would have been moats surrounding these fortified areas. The signal towers spaced between the passes would have been large “lighthouses” used to signal the threat of attack. Each signal tower would have a large stockpile of hay and oils to use for fires and smoke signals. Looking back at warfare, these towers would have been the communication hubs for the northern Chinese defenses. Instead of trying to build tall towers, Chinese engineers took note of the highly variant terrain and built these signal towers in the spots of highest elevation.
Today, this engineering marvel still survives, although there has been extensive renovation work to get it to its current state. Its extreme defensive strength has now dwindled due to modern warfare, but it still stands as one of the largest engineering achievements throughout human history.
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