In 1745, the Shengjing military governor (jiangjun), Daldangga, wrote to the Qian-long emperor (r. 1736–95) to propose building a guard post at the mouth of the Yalu (K. Amnok) River. The suggested place was Mangniushao, a sandbank located where the confluence of two tributaries of the Yalu River, the Caohe and the Aihe, flowed into the mainstream of the Yalu. These tri…