The Imperial City (Vietnamese: Kinh thanh Hue) in Hue is a walled fortress and palace in the former capital of Vietnam. The grounds of the Imperial City were 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 Song Huong (Perfume River) that flows through Hue. This structure is called the citadel. Inside the citadel is the Imperial City, with a perimeter of almost 2.5 kilometers. Inside the Imperial City is the imperial enclosure called the Purple Forbidden City in Vietnamese, a term which follows that used by the Chinese for their own Forbidden City. The enclosure was reserved for the Nguyen imperial family.