Chang'an, the capital city of the Tang Dynasty, was the largest city in the world at that time. It is estimated that during the 13th year of the Tianbao reign of Emperor Xuanzong of Tang (754 AD), there were nearly ten million registered households throughout the Tang Dynasty, with a population of one million in the capital city of Chang'an and the Jingji region. For a large city with such a large population, its food demand is also extremely amazing. Although the Guanzhong Plain where Chang'an is located is known as "a fertile land with thousands of miles, a golden city with plenty of water", and has the advantage of "eight rivers around Chang'an", its actual agricultural carrying capacity cannot fully meet the daily operation of this huge city. The deeper crisis lies in structural consumption. According to the "Food and Commodity Annals" in the New Book of Tang, although the Tianbao period was "rich and substantial in the sea", the ruling class was "arrogant about lost pleasures and did not know how to use them properly, mostly exceeding the amount of goods they used." The grain production in the Guanzhong region not only had to supply the local residents, but also had to support the large and highly consuming non productive class, including the royal family, officials, imperial guards, and various personnel serving the bureaucratic system. How to maintain central stability, ensure the operation of millions of lives, bureaucratic system, and urban economy in Beijing? We have to mention the pearl of Tang Dynasty grain warehouses - Taicang. Since ancient times, China has been well versed in the practice of "storage and accumulation". From the establishment of the Taicang and Changping positions system in the Western Han Dynasty to the evolution of a storage network from the central to local levels in the Tang Dynasty. Tang Dynasty officials said, "Cang, also known as the storage of millet and wheat," and several types of it are recorded in history, including Taicang, Zhengcang, Yicang, Yuncang, and Changpingping. Among them, Taicang has the most special status. It is a large warehouse for storing grain in the capital city, supplying food to millions of people in Chang'an, as well as for the consumption and rewards of the royal family, the salaries of officials, military supplies, and government relief. According to "Guanzi", "one knows etiquette when there are plenty of granaries, and honor and disgrace when there is enough food and clothing." Taicang is not only a physical granary, but also a social stabilizer and lifeline for the million people in Chang'an City. The site selection and architectural design of Taicang in the Tang Dynasty were very particular. The academic community has long debated whether Taicang is located within the "palace city" or the "forbidden garden". This controversy actually reveals the "dual structure" of Taicang's functions, namely the storage points within the palace city that ensure the immediate and safe use of food by the royal family, and the large grain warehouses within the forbidden garden that undertake national strategic reserves and support the population of the capital city. Modern archaeological excavations have provided a key answer to this. A large-scale Tang Dynasty granary site was discovered in the northern forbidden garden of Chang'an City, located in the Longshouyuan highland of the Dabaiyang area in the northern suburbs of Xi'an. Its shape, scale, and layout are highly consistent with historical records of Taicang. The Da Bai Yang granary adopts the form of underground cellar storage. According to the "Book of Agriculture", the underground granary "has neither the consumption of wind, rain, birds, and mice, nor the worries of water, fire, and thieves. Although it is precious and rich in treasures, it cannot be stored." This shows that it was the main form of storing grain in ancient times. For underground grain storage, groundwater is the biggest enemy, and Longshouyuan, where the Great White Poplar Site is located, is a loess plateau that stretches across the north of Chang'an City. The terrain is high and naturally isolates the infiltration of groundwater, ensuring the dryness of the cellar. And the location is adjacent to the canal water system to the north. Canal transport ships from Jianghuai can directly reach nearby docks through the canal. After unloading the grain, they can be transported directly to Taicang in the Forbidden Garden without having to pass through the crowded streets of Fangshi in Chang'an City. This not only ensures efficiency but also isolates civilians, ensuring food security. The Big Poplar Cellar is shaped like a "big mouth, small bottom" cylinder. Referring to the specifications of the Hanjia Warehouse in Luoyang, the diameter of a single cellar can reach 10 to 18 meters and the depth can be 6 to 12 meters. A large cellar can store thousands to 10000 stones of grain, which is equivalent to 500 to 600 tons in modern times. As a major grain storage area in the capital, Taicang maintains a standing reserve of several million stones throughout the year. Such a huge quantity undoubtedly brought storage challenges. In order to preserve food underground for a long time, Tang Dynasty craftsmen designed a complex moisture-proof and insect proof structure. The first step is to dig pits and holes, and after digging the soil cellar, use fire to bake the four walls for a long time to dry and harden them, forming a protective layer similar to pottery. Then, a thick layer of wood ash or charcoal is laid on the bottom and walls of the pit, which is an excellent moisture absorbent. At the same time, the alkaline environment of the charcoal can effectively inhibit the hatching of insect eggs. Lay wooden boards and mats on top of the grass and ash to prevent food from directly contacting the soil wall. After the grain is filled, the top will be covered with thick husks and sealed with soil. This sealed structure creates an oxygen deficient environment, where grains undergo weak respiration in the early stages, consuming residual oxygen in the cellar and releasing carbon dioxide. As oxygen is depleted, a high concentration of carbon dioxide environment forms inside the warehouse, making it impossible for aerobic fungi and stored grain pests to survive. During the same period, there were also Tang Dynasty corn grains in the Hanjia Warehouse site in Luoyang, which have been preserved for thousands of years, but their particle shapes are still clearly distinguishable. The reserve and operation of Taicang not only rely on excellent construction technology, but also on strict systems. The warehouse management in Taicang is very strict, with a set of rigorous procedures and measures from entry, security to exit. Before grain is stored in the warehouse, it must be lifted and thrown. The "Old Book of Tang" records: "When rice reaches the capital, it is mixed with gravel, chaff, and other impurities. At the beginning of the Kaiyuan period, an edict was issued to lift and throw it to compare its reality. The name" lifting and throwing "began from then on. Workers lifted the grain high and used wind power to blow away the husks, dust, and impurities, separating the pure rice. This is not only a cleaning process, but also a means of anti-counterfeiting. Local officials in the Tang Dynasty often added sand, stones, or water to the grain in order to make up for the required amount. "Throwing" could reveal the heavy sand, stones, and frivolous grains in their original form. If it is found that the cleanliness of the grain does not meet the standard, the grain transport officer must be responsible for compensation or supplementation. According to historical records, in order to pass the strict inspection of the Taicang Order, grain transport fleets often had to stay at the dock for several days and self screen several times. If 'throwing' is physical screening, then 'brick inscription' is data traceability. Another vivid example of the strictness of the warehousing system is the large number of engraved bricks at the bottom of the cellars at the Hanjia Warehouse and Dayang site. According to the Tian Sheng decree, the Tang decree states that "when making bricks, the number of dendrobium, year and month, and the names of the officials who received them should be recorded, and the millet should be placed on top of it and covered with straw." These bricks not only bear the origin of the grain, such as "Suzhou Rent Rice," the storage time, such as "Tianbao Eight Years," the quantity and variety, such as millet, rough rice, etc., but also the most critical responsible persons, from the warehouse supervisor to the specific weighing officer, dozens of handling officials' names, which is equivalent to a permanent "responsibility letter." Once there is a problem with the grain, it can be traced back to the person, and the meticulous management is evident. For officials in Chang'an during the Tang Dynasty, Taicang was the source of their monthly livelihood of receiving "rice", and also a microcosm of the officialdom ecology. The salaries of officials in the Tang Dynasty were composed of "rice", "official land", and "miscellaneous use", among which rice was the foundation. Due to the large number of officials in Chang'an, centralized distribution would inevitably lead to congestion. Therefore, the "Six Classics of Tang Dynasty" stipulated a strict system of "installment payment of salaries", where officials of different ranks and different government offices were assigned to go to Taicang on different dates to receive their salaries. However, on every grain release day, there is still a hustle and bustle of vehicles and horses in front of Taicang Gate, often accompanied by a "long queue". Lower level officials often have to queue up early in the morning, enduring long waits and crowding. In addition, due to the huge amount of rice received, high-ranking officials can reach hundreds of stones, and low-level officials can also have dozens of stones, which cannot be transported by individuals, it has given rise to a huge transportation service market outside Taicang Gate. A large number of displaced farmers or urban poor gather here, making a living by selling their physical strength to transport rice for officials. With the gathering of interests, there has also been a phenomenon of "bullying and dominating the market" that monopolizes the transportation market. The hardship of receiving grain and the helplessness of the officialdom left a profound impression on Tang Dynasty poetry. Du Fu wrote about his weariness with the worship of officialdom in "The Gift of Drama after Official Appointment," using the phrase "desolation as a bend in the waist." He also mocked himself for his meager salary and difficulty in obtaining it by saying, "Drinking wine requires a small salary. The rice in Taicang is not only the source of nourishment for life, but also the cause of waist collapse. Taicang is not only a grain depot, but also a metaphor for the prosperous Tang Dynasty. After the An Lushan Rebellion, Du Fu recalled the prosperous era of the Kaiyuan period and wrote the timeless famous line: "Remembering the heyday of the Kaiyuan era, small towns still had thousands of households. Rice flowed with fat, corn was white, and both public and private granaries were abundant." These four lines of poetry are not only a tribute to the past prosperity, but also a picture of the prosperous Tang Dynasty with "granaries" as its core. The rise and fall history of Taicang is essentially a history of the governance ability and resource lifeline of the Tang Dynasty. It leaves behind a profound historical mirror for future generations: the foundation of a strong society is always consolidated in the mountains of "granaries", which are the starting point of etiquette and honor. (New Society)