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The Great Wall of China is undoubtedly one of the world's most iconic structures. With the original sections dating from the 7th century BC, various dynasties and emperors constructed and maintained their own stretches of wall to protect trade and ward off invasions from nomadic groups from the Eurasian Steppe. Collectively spanning over 13,000 miles (20,922 km), it has captivated visitors for centuries as a marvel of architecture and engineering. But do you know about the secret ingredient crucial to the wall's continued existence? Believe it or not, it's rice.
The best-known sections of the Great Wall were constructed by the Ming dynasty, which lasted from 1368 to 1644. In Ming China, sticky rice flour was mixed with slaked lime to create a strong mortar that was used not only in the construction of the Great Wall, but also in many other still-standing buildings (such as city walls, pagodas, and tombs) from the period that have survived historical upheavals and even natural disasters.
So, what exactly makes this mortar so strong? It seems to be the organic-inorganic interaction between amylopectin, a complex carbohydrate found in starchy foods such as rice, and calcium carbonate. The mortar is long-lasting and effective because it's water resistant and holds its shape. Remarkably, the chemical reaction continues over a long period of time, effectively making the mortar even stronger as it ages.
More about the Great Wall:
- The Great Wall of China was named one of the "New 7 Wonders of the World" in 2007.
- Thousands of people died during the construction of the Great Wall, many of whom remain entombed within.
- In many places along the Great Wall, the sticky rice mortar formed such a strong and tight bond with the bricks that it prevented weeds from growing, even hundreds of years after it was set.