Building Beacon Towers to Secure the Liaodong Frontier

During the Chongzhen reign, the skies over Liaodong were heavy with the threat of war. Gu Yanzhou, a live-in son-in-law from a military household in Ningyuan Guard, was full of mathematical knowledge and ingenious ideas, yet constantly looked down on. He foresaw the Later Jin cavalry’s unmatched advantage in field battles and, against the objections of all around him, rebuilt Ningyuan’s defenses around the concept of the “trace italienne.” Using precise terrain surveys, he devised an ingenious “triangular defense system” and used parabolic equations to calculate the dead zones in artillery coverage. In the shadow of the disastrous defeat at Sarhu, he quietly wove an “intelligence network across Liaodong,” training soldiers in basic surveying and intelligence analysis so they could predict enemy commanders’ movements from marching speeds and supply patterns. With a “city-defense simulation table” in hand, he used military operations research to optimize troop deployments. Wielding geometry as his blade and data as his armor, Gu Yanzhou launched a revolution in scientific defense amid the flames of war in late Ming Liaodong, turning the tide when all seemed lost.