Chapter 61: Preparations Against Sudden Gates (Breakout Gates)
Set up a sudden gate (Tu Men) every hundred bu on the city wall. Construct a kiln stove at each sudden gate, and dig a pit four to five chi deep just inside the door. Build a tiled roof over the gate to prevent rainwater from entering.
Assign an official to be in charge of sealing the sudden gate. Prepare two cart wheels and bind them together with wood. Smear the wood with mud and place it inside the sudden gate. Adjust it according to the width of the gate so that it fits securely four to five chi inside the entrance.
Set up a bellows (Tuo) beside the gate, and fill the kiln stove with firewood and mugwort. If the enemy enters through the sudden gate, immediately drop the wooden wheels to seal the entrance, and pump the bellows to blow smoke into the stove, suffocating the enemy.
Note
This chapter details defense tactics for hidden breakout gates. It describes mud-covered wheel barricades, kilns and bellows burning mugwort to create choking smoke, trapping enemy troops that break through these secondary wall openings.
Sudden Gate / Breakout Gate (突门 – Tu Men):
A tactical architectural feature in ancient Chinese siegecraft. These were concealed or secondary gates built into the city walls, designed for defenders to launch surprise counterattacks (sorties) against besiegers. Because they were vulnerable points, they required specialized defensive mechanisms if breached by the enemy.
Chemical/Smoke Warfare:
This chapter provides one of the most vivid ancient records of using smoke as a weapon. By combining a kiln stove, abundant fuel (wood and mugwort), and a bellows (橐), the Mohists created an early form of a smoke generator to asphyxiate or blind invading troops in confined spaces.
Improvised Blast/Smoke Doors:
The use of two cart wheels bound with wood and coated in mud served as a highly effective, quick-deployment barricade. The mud coating was crucial as it acted as a fire retardant, preventing the enemy from easily burning down the wooden seal while the smoke filled the tunnel.
Tuo (橐):
A leather bellows used in ancient China for both metallurgy and, as seen here, military applications. Its inclusion highlights the Mohist school’s deep integration of industrial technology into defensive warfare.
Mugwort (艾 – Ai):
A widely available herb in ancient China, commonly used in moxibustion. Here, its use as a smoke-producing fuel demonstrates the practical, resourceful nature of Mohist defense preparations.
城百步一突门，突门各为窑灶，窦入门四五尺，为其门上瓦屋，毋令水潦能入门中。吏主塞突门，用车两轮，以木束之，涂其上，维置突门内，使度门广狭，令之入门中四五尺。置窑灶，门旁为橐，充灶伏柴艾，寇即入，下轮而塞之，鼓橐而熏之。
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