First built in 1707 and covering over 350 hectares in its heyday, this former imperial resort of the Qing Dynasty (1644-1911) is often thought of as the zenith of Chinese gardening art.

It had been continuously expanded and renovated until 1860, when it was ransacked and set ablaze by the invading Anglo-French allied forces. Up to that point, images of Yuanmingyuan had only been recorded in paintings.

Yuanmingyuan gradually fell into ruin after it was ransacked－a collective psychological blow for the Chinese people－but written records on how this process took place are insufficient, Li pointed out.

According to Liu Yang, deputy director of the Beijing History, Geography and Folk Custom Society, who had collected the photos, some photographers visited the Yuanmingyuan ruins in the late 19th century, and their works became precious historical references showing that some sites survived in 1860 and continued to exist for some time afterward.

In 1861, 13 sites in Yuanmingyuan that partially remained were mentioned in an official Qing Dynasty report, as Liu cited.

"However, the sites were only named, and we could not specifically know how badly they were damaged in 1860," Liu said.

But these newly found photos provide direct clues of what actually took place after 1860. For example, in a group of photos taken in 1882 by Robert de Semalle, a French diplomat based in Beijing, many wooden constructions can be seen.

"Some of them were even in a good condition, as the photos show," Liu said.