The Grassland Capital in the Flood of 1299: Archaeology of Water Conservancy in Xanadu, Yuan Dynasty

Yuan Shangdu was one of the most famous cities in the world in the 13th and 14th centuries. It is also an unprecedented grassland city. Its successful experience in urban flood control and drainage has certain enlightening significance for today's people to deal with natural disasters such as heavy rains and mudslides.

Heavy rains and mountain torrents in Xandu, Yuan

Shangdu of the Yuan Dynasty is located 20 kilometers northeast of Shangduhe Town, Zhenglan Flag, Xilin Gol League, Inner Mongolia Autonomous Region. It is located on the Jinlianchuan Grassland with rich water and grass on the north bank of the Shandian River (i.e. the upper reaches of the Luan River). In 1256, Kublai Khan, who had not yet become a Khan of Mongolia, sent monk Liu Bingzhong to plan and select Jinlian River, which is surrounded by mountains and rich in water, to start building a new city called Kaiping. After three years of construction, the city was initially built. Later, the capital of the Yuan Dynasty. It borders Longgang in the north and the Luanhe River in the south. History praises it as saying: Longgang is covered in the shade, Luanhe River flows through the sun, surrounded by four mountains, and the beautiful atmosphere is lush... The mountains have trees, the water has fish salt, the department stores are in ruins, and animal husbandry is flourishing.

Shangdu of the Yuan Dynasty is located on the desert-loess boundary belt of our country, and its northern boundary is the northernmost reaches of my country's summer monsoon. However, the Jinlianchuan River during the Yuan Dynasty still had a warm and humid climate with abundant rainfall. North of Longgang in the northwest of Xanadu City of the Yuan Dynasty is the vast Hunshandak Sandy Land. Therefore, Longgang is also an important barrier for the capital of the Yuan Dynasty to resist the sandstorms in the north. The Jinlian River south of Longgang is nourished by the Luanhe River system and presents a completely different natural landscape from the north of Longgang. When the winter monsoon comes, this natural barrier blocks the strong cold and dry monsoon blowing from the northwest, reducing the impact of sandstorms in the Hunshandak Sandy Land on Xandu of the Yuan Dynasty. During the summer monsoon, Longgang blocks the westward advance of the southeastern monsoon, causing water vapor to gather and stay on the south side of Longgang to form windward slope rainfall, which moistens the vast Jinlian River south of Longgang. However, in years with strong summer winds, there is too much rainfall in the south of Longgang, which often forms flash floods. The flash floods and floods in the Lightning River will directly threaten Xandu, so the builders and managers of Xandu have to consider flood control issues.

Ancient urban water conservancy project-Tiefangan Canal

The first water conservancy project in Xanadu of the Yuan Dynasty was the Tiefangan Canal, which was named after the Tiefangan standing on the mountain. According to records, it is said that Jinlian River, where Shangdu is located, was once a sea and dragons. When Liu Bingzhong built Shangjing, he used to drive dragons away and built Tiefangan Town. According to archaeological surveys, the Tiefangan Canal is located northwest of the outer side of the west wall of Shangdu City in the Yuan Dynasty, mainly defending against mountain torrents coming from Longgang in the northwest. When Liu Bingzhong first built Kaiping City, because there were many swamps in the land, he set up iron flag poles on the mountain to hold water."The iron pole stands tall and the sea dries up, and the Wolong flies into the sky." There is a description in the poem of the Yuan Dynasty: "There is an iron pole on the West Mountain of Shangjing, which is hundreds of feet high. Because there are dragons in the sea, the Fan family is used to say that it is controlled." The mountain where this iron pole stands is called Tiefangan Mountain.

According to a survey on the top of the Aobao in Hatingtai, northwest of Xanadu, it was found that the bottom diameter of the Aobao piled with stones was about 40 meters and the top height was 8-10 meters. On the west side of Aobao, there is a quarry with a length and width of about 15 meters and a depth of 3-4 meters. On the southeast side of the pit, there is a brown rectangular stone strip 212 cm long, 118 cm wide and 55-61 cm thick in the east-west direction. The surface and four sides of the stone strip are processed and have oblique engraved patterns on them. There are two unpenetrated holes on the front of the stone strip. Mr. Jia Zhoujie believes that this may be the flag pole clip referred to in "Creation Method", that is, the base of the iron flag pole. It can be inferred that Hardentai Aobao is Tiefangan Mountain in Xanadu City of the Yuan Dynasty, and Tiefangan Mountain in Xanadu City of the Yuan Dynasty is located at the top of this mountain. In addition, in the quarry in Hadengtai Oboo, an iron drill was found. It was "about 20 centimeters long and has a cross-section of 1-1.5 centimeters square. It has a pointed head and a curled tail due to multiple beatings."

From north to west of the capital city of the Yuan Dynasty is the continuous Longgang. Between the western end of Longgang and Hadengtai Aobao, about 2000 meters away from the northwest corner of Shangdu Outer City, there is a mountain pass about 1000 meters wide. The northern section of Tiefangan Canal is built between the two mountains. According to current ground surveys, there is a straight flood blocking dam at the foot of the Hadengtai Aobao Mountain to the northeast at the foot of the mountain at the western end of Longgang. It is 1064 meters long, 5.2-5.8 meters wide at the bottom, 2-3.5 meters high, and 32 degrees in direction. Both sides of the dam are wrapped with natural stones and obliquely retracted upwards. The stone walls are about 0.6 meters thick. The outer stone walls are made of white ash and the inner stone walls are made of red clay. The stone wall is rammed with yellow-brown soil, and the rammed layer is 8-10 cm thick. There is an overflow mouth 55 meters northeast of the dam under the Hattai Aobao Mountain. The overflow port is 68 meters wide, with traces of stone walls on both ends. On the inner side of the flood overflow outlet 28 meters to the northeast, there is a northwest to southeast flood discharge channel connected to the flood blocking stone dam.

Regarding this flood control canal, academic circles generally believe that it was designed and built by Guo Shoujing, a great scientist in the Yuan Dynasty. History records: In the second year of Dade (1298),"Duke Zhao (Guo Shoujing) went to the capital and discussed the opening of the Tiefan Canal. The public memorial: "Mountains and rivers fall violently every year. If we have to have large canals and weirs, we must have a width of five or seventy steps." The ruling party is stingy with labor costs, takes public words as a mistake, and reduces its scope by one third. It rained heavily next year, and the mountains and rivers poured down, but the canals couldn't accommodate it. The tents of people and livestock were floating away, and the palace was almost violated. The next day, the emperor hunted north and said to Zaichen: 'Guo Taishi is a god, but unfortunately I don't use his words.'"

The above records do not conclude that the Tiefangan Canal was personally designed and built by Guo Shoujing, a great scientist in the Yuan Dynasty. However, before the construction, Guo Shoujing proposed a construction plan. He believed that the Shangdu River of the Yuan Dynasty had been flooded year after year, and the flood control canal must be 50 steps to 70 steps wide (equivalent to the current 75-105 meters). Such an accurate figure would obviously not be obtained without on-site investigation and calculation. Therefore, the original design plan of the Tiefangan Canal was probably proposed by Guo Shoujing. This flood control canal is likely to be built in the second year of Dade. This should be the earliest urban flood control project recorded in history in Inner Mongolia.

Unfortunately, Guo Shoujing's opinions were not taken seriously. Due to the parsimony of those in power, the design width of the channel was reduced by one-third (50-70 meters), resulting in tragedy.

Construction of flood control and flood discharge facilities

After investigation, the researchers found that on the south side of Xiguan Street, about 100 meters in front of the Lightning River, there is a channel that branches to the southwest and is more than 200 meters long. It is speculated that the channel should have been rebuilt after being diverted westward away from the city wall. At the northeastern end of the stone flood blocking dam and further northeast, along the foot of Longgang Mountain, a similar flood blocking dam is built to connect with it. The dam body is 60 degrees in direction and about 1000 meters long. It may be built to intercept rainwater on the gentle slopes on the south side of Longgang in the north. At the junction of the two dams, an included angle of 120 degrees is formed on the inside. In addition, on the inside of the flood barrier dam, there is also an outer arc-shaped channel more than 30 meters wide. The sides are slightly high and the middle is slightly concave. It seems to be two soil ridges, with a height of 1.5-2 meters. The soil is piled and the tamping layer is unclear. This wide soil ridge is arc-shaped in the southwest and connects to the flood discharge channel, and extends to the angle between the two flood blocking dams in the northeast.

Comprehensive archaeological surveys and reference to literature records, it is not difficult to find that although the flood control canal built in the second year of Dade was damaged by water the following year, only part of the canal was added to it in the later period and was not comprehensively expanded or renovated. The arc-shaped building remains on the inside of the flood blocking dam in the northwest of Shangdu City are likely to be the flood discharge channel newly built after Dade reduced the building scale in the second year. Due to the inability to withstand the flood, a more solid rock-clad flood dam was later built on its outer side. In addition, the flood discharge canal that flows southwest into the Shandian River at the southern end is likely to be built later to ensure the safety of Shangdu.

In addition to flood control projects, there were also drainage projects when the capital was built in the Yuan Dynasty. The capital of the Yuan Dynasty is relatively close to the Luan River, has low terrain, and has a large number of lakes and swamps. Therefore, during the construction of the capital, the problems of draining lake water and blocking water sources were also involved.

Huayan Temple was built in the northeast corner of the Imperial City. According to records, at that time,"the spring water at the base of the temple was boiling, and it was built with tens of thousands of wooden nails, which cost a huge amount of money." According to on-site archaeological surveys, there is a group of temple building sites in the southwest corner of the Imperial City. Outside the west wall of the site, a row of half-meter-high wooden piles, 1.5 meters long, are exposed from the ground. The underground part is cut into a cone. These wooden piles should be the wooden nails in the records. This is also an example of drainage during the construction of Shangdu in the Yuan Dynasty. In addition, in order to drain the stagnant water on the top of the imperial city wall, a 10 cm deep and 20 cm wide water trough was built on the wall skin of the city wall. Xanadu's experience in water control is extremely meaningful even today.

(This article is the result of the special funding of the third phase of the 985 Project of Renmin University of China)

(Author's unit: School of History, Renmin University of China)