Some brass components of timepieces have also been discovered.

Qing Dynasty emperors had a particular interest in European-style timepieces. The Palace Museum's mechanical clock from the 18th and 19th centuries-with parts mostly from the United Kingdom, France and Switzerland-was one of the best in the world.

Emperors were not satisfied with merely being collectors, and during Qianlong's reign the Forbidden City began making its own products.

Xu said: "Follow-up studies of the site need interdisciplinary expertise. For example, we can produce many new findings in the laboratory by analyzing the ceramic samples. Even the soil can significantly help us learn about the natural environment.

"Archaeology in the Forbidden City means much more than filling gaps in historical records that center on royal court politics. We can gradually form a full understanding of ancient society from details that are easily neglected."