In Xichang, Sichuan Province, a restoration project is underway to rebuild the city’s ancient wall. Workers’ tasks include making bricks, laying bricks…and boiling large bowls of rice to cement the bricks together. Informed by a 21st century discovery regarding the ancient methods used to build the original wall, workers seek to stay true to the original Ming Dynasty builders’ techniques. Xichang’s wall is about 900-meters long, so it requires a lot of work. All this may seem slightly unusual—but using glutinous rice, a variety of rice (which has nothing to do with gluten) mainly grown in south and south-east Asia as cement is not a new practice, with the Great Wall of China itself being rumored to have been built partly with the aid of sticky rice.
Every day, the builders put 500 kilograms of glutinous rice on the boil, and then mix this starchy alternative with a few other ingredients, such as limestone, to form a mortar which will hold the wall together. It’s estimated that the entire project will require an impressive total of 50 tons of rice, in all. At the site of construction, five giant pots are heated over coal, and workers must keep stirring the rice inside these pots to prevent it sticking, as they haven’t invented non-stick crockery of these proportions yet.
Glutinous rice, more informally known as “sticky rice’ is the same type of rice cooked in Chinese dishes such as Zongzi ( 粽子), in which it is cooked in the form of a dumpling, mixed with other savory ingredients, and then wrapped into a parcel of bamboo leaves. Zongzi is traditionally eaten at the Dragon Boat Festival, due to the symbolism that the sticky rice has already attained in Chinese culture. Sticky rice is also used by families to make a special type of cake, called nian gao (年糕), for New Year’s celebrations in China, which symbolizes hopes for a better future and has connections to a legend in which rice hidden under a city wall is said to have saved the people’s lives. In a time where China’s economy was based on agriculture, glutinous rice held a status of symbolic and practical importance in a variety of different ways. Now, a lesser-known purpose of sticky rice is being revived in the restoration of Xichang’s city wall.
The city walls of Xichang were first built c.1387 AD, and with the exception of some inevitable damage over time, the wall has reliably withstood natural disasters such as earthquakes, floods, and wars. The same goes for other structures, like pagodas and tombs built in the time of the Ming Dynasty (1368-1644), not to mention certain sections of the Great Wall of China. The use of rice mixture as cement for the construction of significant walls—and other architectural structures—is mainly a product of the Ming Dynasty, although scientists have found that it was first developed about 1,500 years ago.
Parts of the Great Wall—built in different stages over many centuries—were built during the era of the Ming Dynasty. The materials and methods used for building during this period were highly sophisticated, seeing in the practice of using bricks to construct the walls. The Ming sections of the Great Wall are up to 7.5 meters high and five meters wide at the base, and studies show that the endurance of these walls can be traced back to sticky rice.
Of course, there are walls in China other than the Great Wall that are great, and they owe some of this greatness to the rice mixed with limestone which was used in their construction. The city wall of Nanjing, is one such wall. The wall was commissioned under Emperor Zhu Yuanzhang, founder of the Ming Dynasty (r. 1368-1398) and was built to surround his newly built capital city, Nanjing, the first capital in China to be built south of the Yangtze River. The wall was originally 22 miles long and 14-21 meters high, and although much of it has crumbled today, it is the oldest wall in the world. Behind the defense of the emperor’s most important city? Rice.
Much of the Nanjing Wall, built to protect the capital city established by the first Ming Dynsaty emperor, still stands [public domain]
Based on more than a fondness for rice, the ancient Chinese appear to have discovered the merits of sticky rice’s chemical make-up and utilized it accordingly. In the American Chemical Society journal, Dr Zhang, a professor of chemistry at Zhejiang University explains that:
“The organic component is amylopectin, which comes from the porridge of sticky rice that was added to the mortar. The inorganic component is calcium carbonate, and the organic component is amylopectin, which comes from the sticky rice soup added to the mortar. This amylopectin helped create a compact microstructure, [resulting in] more stable physical properties and greater mechanical strength.”
Amyoplectin is a type of complex carbohydrate which is not found in any other variety of rice, and is a large part of the reason that certain historical structures built with this ingredient still stand today—it is thought that the ricey mortar actually gets stronger over time because the chemical reaction keeps recurring. The other ingredient, limestone, if used without the rice mix, wouldn’t have been strong enough to support the walls through earthquake, extreme weather, and military attack, but both ingredients mixed together make for an incredibly strong blend. This secret, only rediscovered by scientists in recent years, is the reason why the Xichang Wall is now been restored using cauldrons of rice pudding.
Similarly, ancient Roman civilization had a particular recipe consisting of volcanic ash that had naturally been heated to a very high temperature, which was superior to many modern methods of mixing concrete, yet was lost after the fall of the Roman Empire. In both cultures, the workers thought that the core ingredients were such common knowledge that they didn’t need to write the recipe down—and so the recipes were lost for centuries before recent archaeological research found out about them.
A skeptic might be inclined to think that the rice-cement method is now being revived as a cheap alternative to cement—it’s not. According to CRI, it costs almost 100 times more to produce the rice cement than it would to simply use conventional cement. The reasons behind spurning the modern cement in favor of the ancient recipe are that it is more efficient, resulting in an “unbreakable” wall, and that it looks more authentic. In the wake of the archaeological discovery that many ancient Chinese walls were built using rice, scientists have tested the strength of the method and confirmed that it is more efficient than ordinary cement.
Cover image from Peggy_Marco