Round Heaven and Square Earth, July 2004.Round Heaven-Square Earth is a branch of the Yin-Yang theory. Siheyuan is its embodiment in architecture. This Siheyuan is located in Xianming Hutong.[Photo by Bai Hao/For chinadaily.com.cn]

"When unrolling a map of Beijing, you will find many places in the city named after tombs," he says.

"But it was difficult to trace the origins of the tombs.

"Unlike the Ming Dynasty (1368-1644), when emperors gave land to princes and nobles anywhere in the country, most of the Qing royals and officials lived in Beijing. That has left many tombs in the city."

The 1950s witnessed large-scale urbanization in Beijing after the city became the capital of New China and many such tombs were gone.