China was home to one of the earliest civilizations in human history. Early Chinese are credited with many revolutionary inventions including paper and gunpowder. And they laid the foundations of the longest man-made structure ever built. In total, The Great Wall of China is 21,000 kilometers long and passes through more than 400 towns across northern and central China. However, contrary to the common view, it is not a single continuous structure. In fact, it is a series of fortifications and bulwarks whose origin can be traced back to the time between the 8th and 5th Centuries BC. At the time China was divided into several smaller states that were always at war with each other to expand their territory. With frequent external threats rulers of these smaller states started to build high walls to keep out intruders.

By the 3rd Century BC, the warring states unified under the Qin Dynasty and their Emperor

set about extending the Wall, while also connecting some of the existing sections. However, the most famous parts of the wall were built much later during the Ming Dynasty, which came to power in the 14th century - about 1,700 years later. Almost one-third of the Wall and some of its strongest sections were built during that era to protect against the Mongol tribes.

The materials used in the Great wall's construction differ greatly depending on the kind of terrain, the wall passed through and the materials available in the surrounding areas. In many places rammed soil and wood were used while the strongest sections of the wall were built using marble, bricks, and a secret ingredient that has preserved it for so many centuries. The secret ingredient is a rather unusual mortar that contains sticky rice. Introduced during the Ming Era, it proved to be as strong and waterproof as cement and sealed the bricks so tightly that weeds were unable to grow between them.

Much of the Ming Era sections are still standing strong to this day, even surviving drastic weather events and earthquakes. But building the longest man-made structure was no easy task. Often, huge stones and massive bricks had to be transported to mountain tops and through difficult terrains. Without powerful machinery, laborers could only use their bare hands and often traveled several kilometers resulting in deaths from hunger and exhaustion. That's why many laborers lost their lives during the construction of the wall. Today, only rough estimates can be made and some articles put the number at around 400,000 deaths.

The Great Wall of China is a testament to the skill and hard work of the millions of laborers and many parts of the wall stood the test of time and continue to attract over 10 million visitors every year. However, this might also become a problem in the future. While innovative mortar solutions and stone blocks have helped preserve the wall, not all of its sections are as well maintained.

Over the years, adverse weather conditions made around one-third of the wall disappear. Human activity including villagers stealing building materials, and excess tourists has also contributed to the wall's decay.

Despite some of its sections disappearing, the Wall's sheer size has given rise to many popular myths including the one that is visible from the moon. However, this myth is incorrect. The claim about its visibility from the moon was first made in the 1930s and no one had traveled to the moon or even to space at that time. The first person to set foot on the moon, Neil Armstrong was also asked about the Great Wall's visibility many times but while he could see continents, lakes, and bodies of water, no man-made structure was visible from the moon.