Treatise on Armament Technology, Volume 114

Military Resources: Defense, Covenant for Forts, Part 1

Iron plating is extremely thin and cannot withstand intense scorching. As the iron heats up, the wooden core of the gate catches fire; destroying it this way requires little effort from an attacker. Furthermore, if there is no overhanging gallery original: 懸樓 xuanlou, a wooden structure projecting from the wall to allow defenders to shoot downward. above the gate to strike the enemy from a distance, and no drainage troughs original: 漏槽 loucao, channels used to pour water or sand down to extinguish fires at the gate. to pour water down, the gate is defenseless.

I have calculated that the strength of a man throwing a bundle of straw can reach nearly ten paces. If a thousand men throw their bundles simultaneously, the straw will pile up into a hill. Once ignited, there is nothing that will not be melted or destroyed. If the gate is ruined, what does it matter how many men you have inside? It will be too late to respond to the crisis.

Therefore, there must be a barbican original: 甕城 wengcheng, literally "urn enclosure," a defensive wall surrounding a city gate.. Its height and thickness must be equal to those of the main fort, and both the inner and outer sides must be equipped with battlements original: 睥睨 pini, the low, crenelated walls atop a rampart for protection.. A side gate should be opened, also using iron-plated doors original: 鐵扇 tieshan, literally "iron fans," referring to the leaves of the gate.. [These designs] have since been consolidated.

Additionally, the barbican gate must also be equipped with drainage troughs for pouring water.