The secrets behind the desolation of Chang’an in the Tang Dynasty

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This post was last edited by yunrun on 2019-7-31 at 19:20. Recently, the highly popular TV series \"The Twelve Hours in Chang’an\" has taken viewers on a journey of imagination to the glorious era of the Tang Dynasty. As one of the most powerful powers in the world at that time, its vast territories, rapidly developing economy, and diverse and open culture all left a significant mark on the Tang Dynasty. http://yunrun.com.cn/upload/201907/30/201907301528068551.png Still images from the drama \"The Twelve Hours of Chang’an\": 1. The Golden Age of the Tang Dynasty ① The prosperous city of Chang’an. As the largest city in the world at that time, and the first city in human history to have a population of one million, the capital city of Chang’an embodied the prosperity and flourishing of the Tang Dynasty to the fullest extent. The area of Tang Chang’an City was 9.7 times that of the area within Xi’an’s city walls today, 1.7 times that of Yuan Dadu, 1.4 times that of Beijing during the Ming and Qing dynasties, and 7 times that of ancient Rome. http://yunrun.com.cn/upload/201907/30/201907301531242844.png Map of Chang’an City. It is grand in scale, carefully planned, symmetric in structure, and neatly arranged. The six main streets that pass through the twelve city gates serve as the city’s primary traffic routes. There are 11 streets running from north to south and 14 streets running from east to west within the city, which divide the residential areas into 110 neatly organized districts. The five-kilometer-long Zhuque Street runs from north to south, serving as the central axis of Chang’an City. Countless poems and verses fill one with admiration for the splendor of Chang’an. “\"The celestial gates open to reveal the palaces; rulers from all nations come to pay homage to the imperial crown.\" As the center of the world, Chang’an attracted a large number of foreign envoys and pilgrims. “\"Looking back at Chang’an, its beauty is like a pile of embroidered fabrics; on the mountain top, thousands of gates stand in orderly rows.\" With just these two lines, the beauty of Lishan Mountain and the grandeur of its gates are etched into people’s hearts. Such Chang’an could certainly be regarded as the \"top-tier\" city of its time. But why, after the Tang Dynasty, did the Song Dynasty not continue to use the prosperous city of Chang’an, but instead choose to move the capital to Bianjing (Bianliang, present-day Kaifeng in Henan)? ②The underlying chaos: Apart from the external factors of continuous warfare in Chang’an toward the end of the Tang Dynasty, another major and hidden cause that persisted for a hundred years was the degradation of natural resources, especially water resources. It should be noted that the Guanzhong Plain, where Chang’an is located, was originally a region with fertile lands stretching for miles and dense forests, boasting a beautiful ecological environment. Around Chang’an, there are eight rivers – the Wei, Jing, Feng, Lao, Yi, He, Chan, and Ba – surrounding the area. Thanks to these water resources, irrigation for farmland in the Guanzhong region is convenient: “The land there is fertile and vast; it has been used as premium farmland since the times of Yu and Xia.” However, at its peak, the permanent population of Tang Chang’an City was 1.85 million, while the floating population was 510,000. To feed these people over the long term requires a large amount of resources, and it also generates a great deal of waste. With a population of one million in Chang’an City, the amount of waste generated on a daily basis was enormous. How did the people of the Tang Dynasty deal with it? Is waste sorting also carried out? a. For mixed waste, the people of Chang’an dig a hole in the ground to connect it to the underground river. Then, place a lid with holes on the ground (as a leak-proof measure) and pour all the trash into it. As a result, solid waste remains on the surface, while sewage, excreta, and the like flow into underground rivers. b. Liquid waste, such as excreta and sewage, was simply poured directly into the drainage channels at that time. Over time, sewage caused the groundwater to become halinated, making it bitter and salty and completely unfit for drinking. The lack of water sources was also one of the key reasons for the decline of Chang’an during the late Tang Dynasty. http://yunrun.com.cn/upload/201907/30/201907301536438319.png Although Chang’an had the advantage of being surrounded by eight rivers, its loose soil made it prone to subsidence; as a result, open channels were used instead of underground ones, so one can imagine the poor sanitary conditions there. According to \"Youyang Zazu,\" it is recorded: \"I used to read the five volumes of \"Ruina Jia\" on a regular basis, and it caused me a great deal of disturbance; the words blurred before my eyes, and I couldn’t stop reading them.\" ”Describing a person reading, with flies all over their eyes, shows that they are plagued by dirt and mess. http://yunrun.com.cn/upload/201907/30/201907301547099614.png By the end of the Tang Dynasty, the flow rates of rivers such as the Jing River, Wei River, and Ba River had become increasingly low, and artificial channels like the Longshou Canal and Qingming Canal also dried up one after another. Such a place, lacking in water sources and filled with foul odors, was certainly not a suitable choice as the capital of a country. Were the drainage systems of ancient cities of the same type all underdeveloped? In fact, the other civilization at its peak – ancient Roman civilization – had a fairly advanced drainage system. 2. Ancient Roman Civilization: In the process of its establishment and governance, ancient Rome absorbed and built upon the achievements of various earlier ancient civilizations, creating its own civilization as a result; it is considered one of the most important sources of Western civilization. Did Rome, the capital city that spanned the three continents of Europe, Asia, and Africa, face the same problems as Chang’an? http://yunrun.com.cn/upload/201907/30/201907301548571669.png ①Advanced drainage system: In ancient Rome, sewage disposal was not as simple and crude as it was in Chang’an. A good water supply system was established as early as the 1st century, which **improved the drinking water situation for local residents. It should be noted that in many parts of Europe, clean drinking water is quite scarce; in order to maintain their health, some Europeans are forced to rely on alcohol to replenish their body’s water supply. But back then in Rome, there were even public toilets and a complete sewage system, something that many places have not been able to match even centuries later. http://yunrun.com.cn/upload/201907/30/201907301550550658.png Public toilets in ancient Rome (Image source: Sohu.com) But having a proper drainage system does not mean that wastewater can be handled effectively. ②The persistently high mortality rate meant that using the toilets in ancient Rome was nothing short of a life-threatening endeavor. Due to the lack of regular cleaning, methane gas accumulated in these toilets and could explode at any moment, leading to death... As people risked their lives using these toilets, the walls of them were often covered with exorcistic spells. Some people even carry statues of the Goddess of Luck with them while using the toilet; there are even rumors that ancient Romans would pray to such statues for safety before entering the toilet. http://yunrun.com.cn/upload/201907/30/201907301552150405.png What’s more terrifying is that, after the establishment of the drainage system, the parasite infection rate among the Romans actually increased. The drainage system removed wastewater from the city, but the Romans used the collected wastewater directly to irrigate their crops. Using human feces as fertilizer is safe, provided that the waste is given enough time to compost and decompose, so that the parasites die and only the portion that can provide nutrients for crops remains. ③Home composting. These two outstanding ancient civilizations suffer from the problem of sewage due to their large city sizes and large populations. In the major cities of today’s world, even as the size of these cities continues to grow rapidly, advancements in wastewater treatment technology have enabled most of the problems to be resolved. However, with increasingly stringent legal requirements, shrinking budgets, and rising complexity in processes, the water and wastewater treatment industry will face unprecedented challenges. http://yunrun.com.cn/upload/201907/30/201907301554184892.png 3. Modern urban water and wastewater treatment technologies: Today, advanced drinking water treatment technologies make it easier to obtain clean water, and they also help protect people from related diseases. People strive to ensure the safety of drinking water through steps such as flocculation and sedimentation, filtration and adsorption, and disinfection. http://yunrun.com.cn/upload/201907/30/201907301556222037.png Drinking water treatment process: Through long-term infrastructure development, the drainage network has now been fully undergrounded, and the problem of odors from open channels in Chang’an City no longer exists. Wastewater can be discharged back into rivers after undergoing physical separation, biochemical aeration, effluent filtration, and disinfection. And if the separated sludge is not handled properly, it can lead to the so-called “toilet explosions” in ancient Rome, which were actually methane gas explosions. http://yunrun.com.cn/upload/201907/30/201907301557388019.png Sludge treatment: When sludge is handled properly, not only are accidents related to biogas avoided, but the resulting gas can also be reused as a source of energy for power plants. The treated biogas residue can be used as fertilizer and is harmless to humans, making it a true example of turning waste into treasure. Analyzers for COD, ammonia nitrogen, total phosphorus, and total nitrogen in wastewater treatment plants: In modern wastewater treatment plants, the main substances that need to be removed are carbon, nitrogen, and phosphorus. To determine whether the removal levels of these substances meet the standard requirements, it is necessary to equip the wastewater treatment process with appropriate instruments, including those for measuring COD, ammonia nitrogen, total phosphorus, and total nitrogen.