Cloud Ladder

The cloud ladder, known in Chinese as yunti, is an ancient Chinese siege weapon consisting of a long extendable ladder mounted on a wheeled chassis and often reinforced with a counterweight or hoist mechanism, used by besieging armies to scale the walls of fortified cities. The weapon is described in the Mozi, a Chinese philosophical text compiled by followers of the philosopher Mozi during the Warring States period of the fifth through third centuries BCE, whose chapters on siege defense are among the oldest surviving detailed descriptions of siege engineering anywhere in the world, presenting the cloud ladder alongside chapters describing countermeasures a defending garrison could use against it, including counter-ladders and fire. Later Chinese dynasties continued to refine wheeled and hinged ladder designs long after the Warring States period, and the cloud ladder's early, systematic treatment in the Mozi is frequently cited as evidence of the sophistication of Chinese siege engineering at a period roughly contemporary with the classical Greek world.