The 105m high Ngu Binh Mountain has a symmetric figure. On both sides of the Even Mount (Bang Son) are 2 small mounts called Ta Bat Son (Left Mount) and Huu Bat Son (Right Mount). After observing that Bang Son resembled a screen, the Nguyễn emperor decided to build up Huế which became known as their Forbidden Purple City. Emperor Gia Long approved the design of geomancers which chose this mount as a front altar of the imposing and solid defending wall system, and renamed it Ngu Binh.