Time as well as the dynastic rise and fall over history has greatly changed the appearance of this complex, especially after the 19th century when the capital was moved southward to Hue during the Nguyen Dynasty. Many royal constructions above the ground were gradually replaced by Western-style office buildings during the rule of the French.

Standing on the site, Wu still says he feels "familiar yet fresh", imagining the grandeur of that former Vietnamese royal palace. In his eyes, a system of architectural remains, foundations of palaces, and rich archaeological findings have told a lot about its past, including frequent communications with China.

Surely, even for a common visitor, it is difficult to stand in front of Doan Mon, the southern gate of the imperial citadel, without noticing the two Chinese characters revealing its name above its central doorway. The gate also has five doorways, just like the Forbidden City in Beijing.

This existing gate, one of the few intact structures within the citadel that is from the imperial period, dates back to the early Le So Dynasty (1428-1527), roughly around the same time when Beijing's Forbidden City arose.

"There are close links between the unearthed relics of the Thang Long ruins and those from three early Ming Chinese palatial cities," Wu says. "We sometimes need a new perspective and a global context to better understand the lineage and characteristics of Chinese palatial constructions.

"For example, as we see the exquisite constructional components of the Forbidden City in Beijing, we often wonder how they evolved into the current peak of techniques," he adds. "Thanks to the earlier relics spanning a much larger time spectrum, we may have crucial references on prototypes of the craftsmanship."