In 1802, after defeating the Tay Son dynasty and reunifying Vietnam from the northern border to the southern tip, Nguyen Anh ascended the throne as Emperor Gia Long and chose Hue as the capital of the new Nguyen dynasty.
The Imperial Citadel of Hue was constructed according to a fusion of Eastern citadel architecture and French Vauban-style defensive engineering. The outer Citadel enclosed the Imperial City, which in turn surrounded the Forbidden Purple City — the emperor's private quarters. Construction spanned several decades and mobilized tens of thousands of workers.
Hue served as the political, cultural, and religious center of Vietnam for 143 years under the Nguyen dynasty. The architectural legacy of this era — royal tombs, sacrificial altars, and palaces — survives to this day and forms the basis for Hue's recognition as a UNESCO World Heritage Site.