Walking in the Rain, July 2007.[Photo by Bai Hao/For chinadaily.com.cn]

"I found that it wasn't enough to focus only on tombs. I saw that many residences were demolished due to lucrative real estate development at the time and some changes were irreversible," he recalls.

"Some hutong areas were developed in the Yuan Dynasty (1271-1368), and are older than the Qing residences and tombs. They are the roots of today's Beijing.

"So I decided to widen my scope."

Old residences of Qing nobles, for example, comprise a major part of his research.

Though Beijing has no official statistics on how many Qing noble residences survive in the city, Bai estimates there are nearly 40 with only prince-level mansions accounted for, but four have been demolished since 1998.