Qianlong's secret garden for his old age

In the Forbidden City, a retired ruler made a refuge for himself which is now being lovingly restored

Even before he abdicated the throne, the Emperor Qianlong was already preparing for retirement. He had a two-acre private courtyard built and filled it with his favorite books, art and a wall mural that brought his garden inside even when he could not go out to enjoy it.

This was the emperor's personal retreat, Juanqinzhai, more known to antiquities experts as the Qianlong Garden. Its name, which alludes to "rest after a lifetime of work", reflected Qianlong's love of scholarship and the arts. He prided himself as an accomplished calligrapher and he is known for his huge collection of art and antiques.

Much of this has been lost, plundered by the turbulent times that China went through before it finally emerged, cleansed and ready for new beginnings. But there is enough left within the courtyard to make it very interesting to the experts.

Built in the 1770s, Juanqinzhai fell into disrepair after China's last emperor, Puyi, was expelled from the Forbidden City in 1924. For decades, it suffered the fate of being forgotten, a decrepit storage space.

The World Monuments Fund (WMF) from the US has played a key role in its restoration with not only funds but also expertise, according to Nancy Berliner, curator of Chinese art at the Peabody Essex Museum.

The $3-million project can be seen as a good example of international cooperation in cultural relics conservation, says Li Ji, deputy director of the Palace Museum. "The cooperation with the WMF was the first major collaboration between a US conservation group and the Palace Museum."

The WMF starting working with the Palace Museum in 2002 to restore the Qianlong Garden and helped train Chinese conservators as they faced the many complex challenges posed by the fragile historic interior and its unusual mix of materials and techniques.

One such was the wall mural that stretched over the ceiling of the room where a miniature stage was built for opera performances, one of Qianlong's loves. It is a detailed depiction of the palace gardens complete with lilacs and trailing purple wisteria. Craftsmen spent much time and money matching the unusual pigments used for the trompe l'oeil, and this was where the expertise from the WMF came in most useful.

This joint conservation exercise has proved so successful that the WMF, a New York-based non-profit organization, signed a broader agreement to restore all 24 buildings and the elaborate outdoor courtyards of the entire Qianlong Garden.

The expected date of completion will be in 2019, a year before the Forbidden City marks 600 years of existence.