Planning and Construction History of the Eight Columns, Anti-Mongol Stone Fortress in the Sichuan Theater at the end of the Southern Song Dynasty

In 1279, Yao Sui, a Yuan official, documented the eight mountain fortresses planned by Yu Jie, the Military Intendant of the Sichuan Theater from 1242 to 1253, in the posthumous biography of Li Dehui, including the Yundingcheng Fortress, the Yunshangcheng Fortress, the Dahuocheng Fortress, the Dehancheng Fortress, the Baidicheng Fortress, the Diaoyucheng Fortress, and the Kuzhuai Fort. Collectively known as the "Eight Columns," these fortresses formed the core of Yu's Sichuan Mountain Fortress System and played a pivotal role. During the Song-Mongol War, Yu devised a defensive strategy based on Song's river defense strategy and the geographical advantages in the Sichuan Basin, and practiced it into a regional defense system. He commanded local governors and generals to lead their troops and populace in constructing mountain fortresses and to relocated the governments into these new fortresses. Relying on the mountain fortress system, the Song armies in Sichuan successfully repelled the Mongol cavalry and defended the upper reaches of the Yangtze River for 37 years. The pivotal event of the 13th century was the death of Möngke Khan during the siege of the Diaoyucheng Fortress, which had a profound impact on Eurasia and made the "Eight Columns" became well-known in both the East and the West. Following the war, the majority of the "Eight Columns" were abandoned and enveloped in the earth. However, as systematic archaeological excavations advanced, well-preserved stone structures, including walls, stylobates, and ponds, gradually emerged from the ground. Based on historical documents, historical images, and on-site field surveys, by introducing the perspective of military history and combining in-depth reading of archaeological reports, this study analyzes the theater and mountain city levels to delve into Yu's initiation of the mountain fortress system, the significance of the "Eight Columns" within this system, and the planning and construction processes undertaken by officials and generals during Yu's tenure from 1242 to 1253. The study elucidates the interplay between military ideas and the wisdom of fortress planning and construction, highlights construction technologies employed, and explores the wartime implementation of the official fortification planning and construction regulations. Firstly, the theater-level research analyzes the influence of Yu's strategies on the system's structure and construction strategy, illustrating the "Eight Columns" role within the system. Yu's strategy of divisional defense and river defense resulted in a defensive pattern comprising one defense line, two defense zones, and one key pass in the Sichuan Theater: the Yangtze River defense line, the East Sichuan defense zone, the Chengdu Plain defense zone, and the Jianmen Pass. His logistical strategy, based on military transportation, led to the Jintun Strategy, which supported fortress construction in the northern no-man's land by transporting troops and supplies from the hinterland along rivers, contributing to a hierarchical system encompassing the Yangtze and its tributary subsystems. Fortresses with three functions emerged, and three site selection strategies were formed: frontier strongholds controlling transport, logistical centers for self-defense, and hubs occupying hilltops and flatlands. The "Eight Columns" not only defined the boundaries of the defense zones but also outlined logistical routes, providing the framework for subsequent system expansion and becoming a key target for the Mongol army. Furthermore, relying on the case studies of three columns, which represent the three types of the "Eight Columns", the Diaoyucheng Fortress and the Yundingcheng Fortress, the research at the level of fortress analyzes the process of their planning and construction, to explore the principles and the technologies, and to discuss how the defense strategies and tactics of different types of armies impacted on the site selection, spatial organization, and the fortification construction of the fortresses. The Diaoyucheng Fortress is a typical example of the river defense mountain fortress built by the naval forces reorganized by Yu. Yu was involved in its construction, and he chose the site and ordered Ran Pu and Ran Jin to build it with the armies of the Lirongsi. The Diaoyucheng Fortress was transformed from a pre-war granary fort at the hinterland to a wartime stronghold at the frontline. Yu’s logistical strategy and his tactics of naval battling at the field and battling for defense lead to a particular form, including the site on the mesa on peninsular, the dustpan layout, and the fort cluster. This form developed into the paradigm of the Diaoyucheng Fortress, which was disseminated to the new fortresses along the Yangtze River, Jialing River, and Qujiang River by the generals sent by Yu to build new fortresses. The Yundingcheng Fortress is a representative of the land defense mountain fortress built by the frontier garrisons, and it was constructed by the Lijongsi army that retreated southward from the Qinling defense line in the early stages of the war. This fortress underwent a process of transformation from a pre-war mountain temple to a wartime mountain fortress. The supply strategies of military-civilian cooperation and the defense strategy of occupying the mountain and the temple led to the twin-city structure and its multi-group layout. The rib arch structure unique to the Chengdu Plain was used to build the gates of the Yundingcheng Fortress. Focusing on the interaction between the planning and construction, as well as its relationship to military strategy in the construction process of the "Eight Columns", this study explores how strategies and tactics were manifested in the planning and construction of the "Eight Columns," and how the principle and techniques supported tactics and strategies. The planning ideology emphasizing on pragmatism and environment in the Song Dynasty, the well-developed management system of fortification planning and construction with flexibility in practice, and the flourishing local construction techniques provided the necessary conditions for this. These factors were crucial in enabling the Southern Song garrison in Sichuan to hold out for an extended period during the Song-Mongol War.