The Imperial City of Hue was surrounded by a wall 2 kilometers by 2 kilometers, and the walls were surrounded by a moat. The water from the moat was taken from the Huong River (Perfume River) that flows through Hue. This structure is called the citadel. In June 1802, Nguyen Phuc Anh took control of Vietnam and proclaimed himself Emperor Gia Long. His rule was recognized by China in 1804, the same year construction began on the new palace and citadel. Thousands of workers were forced to produce a wall and moat, 10 kilometers long. Initially the walls were earthen, but later these earthen walls were replaced by stone walls, two meters thick. The citadel was oriented to face the Huong River to the east.