In 1366 AD, two years before the establishment of the Ming Dynasty, Zhu Yuanzhang issued the "City Construction Order". It was not until 1393 AD that the Ming Dynasty's Nanjing capital city wall, including the palace city, imperial city, capital city, and outer walls, was finally built. After more than 600 years of transformation, the city wall still stands at 25.1 kilometers, making it the longest, largest, and best preserved ancient city wall in the world. It still stands tall and majestic, but the original defense works have become a great place for citizens to relax and tourists to check in today. In Zhonghua Gate Wengcheng, you can admire the Da Bao'en Temple Pagoda, admire the Qinhuai River outside, and appreciate the exquisite ancient defense works; In the Taicheng section, you can overlook Purple Mountain, Xuanwu Lake, and the Medicine Buddha Pagoda of Gujiming Temple; In the Stone City section, one can imagine the Three Kingdoms war fires and feel the grandeur of Jinling's "tiger and dragon" situation... Xu Beihong once lamented that Nanjing City "stands like a human belt, looking like it, and is warm and delicious". Liu Donghua, director of the Nanjing City Wall Protection and Management Center, told reporters that since the 1980s, the Nanjing City Wall has undergone more than 60 protection and repairs, and has shifted from salvage protection to preventive and systematic protection. It has also shifted from focusing on the protection of cultural relics to the overall protection of cultural relics, surrounding environment, and cultural ecology. "In the past, the city wall protected us, but today we protect the city wall. Technology empowers dynamic monitoring of the construction of the Ming Dynasty's Nanjing capital city, breaking away from the old square or rectangular system, and building cities along the direction of mountains and water systems based on the Six Dynasties' Jiankang City and the Southern Tang's Jinling City. The Qinhuai River outside the south is a natural moat, with Zhongshan as its support to the east and Houhu as its screen to the north. The Cina Stone City enters the interior, forming a unique style of city walls. But the city wall itself has been plagued by various diseases due to the influence of climate, environment, plants, and other factors. Since 2010, the Nanjing City Wall Protection and Management Center has been monitoring the structural stability of important defects discovered during daily inspections of the city wall, including cracks, swelling, displacement, and settlement. On April 1, 2015, the "Nanjing City Wall Protection Regulations" officially came into effect, delineating the scope of city wall protection, clarifying prohibited behaviors, and increasing the protection of the city wall at the legislative level. On the exterior walls of the Nanjing city wall, sometimes you can see some gray and white thin tubes, with a rectangular box attached below. This is the automated monitoring equipment of the city wall, and the collected data is transmitted in real-time to the Nanjing city wall monitoring and warning platform. This system, built in 2021, relies on 263 sets of automated monitoring equipment installed along the entire line to continuously monitor 1575 points. The reporter saw in the monitoring hall that there are 369 disease points monitored daily, including 7 types of diseases such as settlement, weathering, expansion, displacement, strain, cracks, and inclination. It is understood that since its launch, the monitoring and warning platform has regularly collected data on the city wall, analyzed changes, and identified thousands of risk points. In addition to relying on machine monitoring, manual patrols still play an irreplaceable role in daily monitoring. Every day, dedicated personnel patrol the city walls in sections, especially for diseases such as weathering. Manual monitoring and machine monitoring complement each other very well. "A patrol officer told reporters that every time he goes out, he carries a handheld device and uses his accumulated experience to take photos and upload the diseases and dangerous situations that need to be dealt with. During a patrol, he discovered loose bricks on the exterior of the city wall in the Jiefangmen section and promptly reported them through the system. Later, repairs were made during maintenance to avoid cracks. The Nanjing city wall is made of city bricks and stone blocks. The bonding materials between the bricks have gradually weathered into organic matter suitable for plant growth due to centuries of wind and sun exposure. When plant seeds fall onto the city wall, they can take root and grow everywhere with the direction of the soil. Some plants with thicker roots will compress the bricks inside the wall, causing them to loosen and crack. And this potential disease cannot be detected by machines yet, and can only be completed manually. If there is an alarm in the monitoring system, the patrol officer needs to go to the scene for review. By monitoring changes in data, combined with daily inspections and annual disease surveys, analyzing the development trend of diseases, and qualitatively grading the risks and hidden dangers of Nanjing City Wall, it is divided into four levels: A, B, C, and D. Corresponding treatment requirements are proposed according to different levels. The protection of the Ming city wall lies not only in the existing structure, but also in the scattered old city wall bricks. In the urban construction of the 1950s, some sections of the city walls were artificially demolished and renovated, resulting in a large amount of wall bricks being lost and scattered. Some were buried as construction waste, while others were used for building construction. In the later demolition of old residential areas, it is common to find Ming city bricks. In order to bring these Ming city bricks back to the mother body of the city wall, in November 2016, the Nanjing City Wall Protection Management Center and the Nanjing Ancient Capital City Wall Protection Foundation jointly launched the "Grain Returning Warehouse to Protect the City Wall" activity, collecting scattered clues of the city wall bricks. Pomegranate New Village, Guanghua Gate, Hohai University, Nanjing Electromagnetic Factory, Qilin Gate... With the continuous attention of enthusiastic citizens, these locations have become recycling points for city wall bricks, with a total of more than 500000 pieces of bricks collected so far. The Ming City Wall, which has undergone over 600 years of scientific restoration with minimal intervention, can still become an important component of Nanjing's landscape city forest, thanks to 40 years of scientific restoration. Liu Caixia, Director of the Cultural Relics Protection Department of the Nanjing City Wall Protection Management Center, told reporters that following the principles of minimal intervention and scientific repair, the "Nanjing City Wall Protection Plan (2008-2025)" and "Technical Guidelines for Nanjing City Wall Protection and Repair" have been formulated. Over the years, research has been conducted on the production standards of bricks for Nanjing City Wall protection and repair, the degradation mechanism and reinforcement measures of the "Baoshan style" city wall bearing capacity, the impact mechanism and removal methods of plant roots on the city wall, the fine evaluation of the reasonable repair scope of apparent diseases on the Nanjing City Wall, and the prevention and control technology of water damage diseases on the Nanjing City Wall. The hidden danger of rainwater has always been one of the main factors causing the swelling and cracking of city walls. In previous years of repairs, waterproof treatment of the top of the city wall has been the key to the repair. Due to the difficulty in verifying and implementing mixed waterproof materials using traditional techniques, with the development and progress of technology, the city wall protection team has explored the use of a new type of material - polymer, which has similar and better performance than traditional materials - to improve the waterproofing of the top of the city wall. After sufficient experimentation and expert verification, it has been successfully tested and utilized during the renovation process of the city wall from Dongshuiguan to Wudingmen. In the specific repair of city walls, it is difficult to repair the Baoshan Wall, surrounding scenic spots, and residential buildings. During the repair process of Baoshan Wall, there is a risk of landslides, and the repair operations of surrounding scenic spots and residential buildings are restricted. At around 5:00 am on November 27, 2016, a partial collapse occurred on the south side of the city wall in Xiaotaoyuan Park. The Xiaotaoyuan City Wall is built along the mountain, closely adjacent to the mountain. Tall trees stretch out in rows towards the wall, and below the wall is a residential fitness square. Standing under the city wall, one can still vaguely see an inverted "eight shaped" dividing line between the old and new city walls, with a collapsed length of about 20 meters. According to the staff, continuous rainfall caused displacement of the soil slope on the inner side of the city wall, resulting in the displacement of the wall and ultimately leading to the collapse of some parts of the wall. After the collapse, the reinforcement and repair plan of the city wall and upper body has been demonstrated by many experts and approved by the National Cutural Heritage Administration before implementation. The protection and repair work of this section of the city wall includes stabilizing and strengthening the soil slope behind the wall in the collapsed section by using the pile anchor structure, cleaning the residual wall in the collapsed section, and building and restoring the city wall body again; Dismantle and rebuild the bulging and loose local walls on both sides of the collapsed section, redo the traditional waterproof layer on the top of the city wall, restore the drainage ditch on the east side of the wall top and the guardrail on the west side. Due to the collapsed city wall being surrounded by mountains on the inner side and residential fitness and park trails on the outer side, large machinery cannot enter, and all collapse cleaning, reinforcement, and repair operations are carried out manually The staff who participated in the repair at that time recalled that in order to reduce the impact of construction operations on the city wall, manual excavation was used for pile foundation construction. Due to the rainy and snowy weather during the construction, each pile hole was equipped with a rain cover to prevent rainwater from entering. The risk of mountain sliding in this section of the city wall was resolved through excavation, slope making, and pile anchor construction. In order to maintain the original appearance of this section of the city wall, the exterior of the city wall is repaired using recycled old city wall bricks, and the top surface is paved with new city wall bricks, taking into account factors such as tourist walking and freeze-thaw rainwater. In order to completely solve the impact of mountain rainwater on the city wall, a flexible waterproof layer was added to the top of the city wall, and drainage ditches were added between the mountain and the city wall to orderly drain the water from the mountain. Tourists visiting Zhongshan Botanical Garden can walk to the Qianhu area and see a unique section of Ming city wall across the lake. The two remaining sections are connected by a steel frame structure. In 1991, heavy rain in Nanjing caused the collapse of the Qianhu section of the city wall. In 1998, during the cleanup of the collapsed city wall, a section of the city wall built by Ming Hongwu in the early days was discovered. It was only half the height of the current Ming city wall and had a typical "wall within a wall" structure. This structure has also been found in other sections of the city wall, such as the site of the Southern Tang Fugui Tower in the Ming city wall. At the same time, during the investigation of the current situation of the Qianhu breach wall, a water gate was discovered. This water gate was built in the early Ming Dynasty and is one of the important water supply systems of the Yudai River in the city, providing important empirical evidence for studying the water supply and drainage system of the Ming city wall. On the premise of preserving authenticity and integrity, an attempt was made to carry out identifiable and reversible repairs on this section of the city wall. In the form of exposed steel structure frame, the two disconnected sections of the city wall are connected, and the steel ladder for climbing the city wall is provided. As a sunken square, the Banshanyuan Sluice, which has been protected and repaired, is also open to the public, giving consideration to the display of historical information and the activation and utilization of cultural relics. The National Cutural Heritage Administration calls it "an innovative measure for the protection of cultural relics in China". The revitalization and utilization of digital technology continues on the east side of Zhonghua Gate Wengcheng. There is a modern building in the same color as the city wall. Walking along the slope like a horse road to the roof, what you see is the city wall. This building is the Nanjing City Wall Museum, which was just awarded the national first-class museum this year. Ma Lin, Deputy Director of the Nanjing City Wall Protection and Management Center, introduced that as the largest city wall themed museum in China, it is closely connected to the Zhonghua Gate section of the city wall in geographical space. The basic exhibition revolves around the theme of "unparalleled city wall", showcasing more than 2000 cultural relics (sets) from five aspects: design ideas, construction techniques, imperial majesty, military defense, and heritage inheritance. It focuses on showcasing the historical, cultural, technological, military and other values of the Nanjing City Wall, forming a "museum+heritage site" response. Although memories can be salvaged in history, only by connecting with people's real lives can they continue to thrive. The Bai Xia Suo Yan records: "In the first month of the year, visitors to the city are like ants, and the sound of flutes, drums, and firecrackers can be heard from afar. It is called 'walking away from all diseases', and it is also said that' stepping on peace '. The custom of "climbing the city on the 16th day of the first lunar month, stepping on peace, and walking through various illnesses" has continued in Nanjing to this day. As a traditional Chinese cultural custom, hanging couplets at the city gates and holding city wall lantern festivals during the Spring Festival has become an important part of our festival, just like climbing the city walls. Taking advantage of the architectural characteristics of the city wall itself, exhibition spaces were set up in the heritage sites along the city wall, such as the Zhonghua Gate caves of fighters garrison, the South Tang Dynasty Fu Gui Tower site, and the Qingliang Mountain Stone City site, creating the "exhibition settlement along the city wall" of Nanjing. Create an immersive offline live performance of "Heart Seal · Zhonghua Gate" and expand night tours