The Imperial City in Huế 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 Huong River (Perfume River) that flows through Huế. This structure is called the citadel. Inside the citadel was the Imperial City, with a perimeter of almost 2.5 kilometers. Inside the Imperial City was the imperial enclosure called the Purple Forbidden City in Vietnamese.