Workers pull weeds at the Yuanying Guan ruins at Yuanmingyuan, or Old Summer Palace, in preparation for a project to preserve the standing pillars. 

The surviving remnants of columns and gates in Beijing's Yuanmingyuan - or Old Summer Palace - will be reinforced to prevent them from collapsing, park officials said on Wednesday.

The ruins have been preserved for nearly 160 years as a symbol of the nation's collective pain after they were destroyed by foreign military forces in the mid-19th century.

Foundations of the stone remnants in the ruins of Yuanying Guan (Immense Ocean Observatory) will be strengthened as part of the project, which will last until late September, according to the administrative office of Yuanmingyuan Ruins Park.

Yuanying Guan, which covers 1,465 square meters is a key site in the Xiyang Lou (Western Mansions) area of Yuanmingyuan. Its construction lasted from 1759 to 1783 during the reign of Emperor Qianlong in the Qing Dynasty (1644-1911).

Construction of Yuanmingyuan began in 1707 and continued for more than a century. Spectacularly beautiful at its peak, it is often referred to as "the garden of gardens", with its lush landscapes dotted with numerous temples, palaces and pavilions. Its 350-hectare area is about five times that of the Forbidden City in central Beijing.

Besides functioning as an imperial resort, it was also a place where four Qing emperors (Qianlong, Jiaqing, Daoguang and Xianfeng) often handled affairs of state until 1860, when it was wrecked by invading Anglo-French expeditionary forces during the Second Opium War (1856-60).

"Yuanmingyuan is the zenith of Chinese gardens," said Liu Xiaodong, director of planning department of the administrative office. "Xiyang Lou is a perfect combination of European architecture and Chinese skills - an example of cultural communication between the West and China."

Over time, rain, freezing and looting (villagers often took materials from the ruins to build their own houses during the 20th century's social upheavals) have made the few standing columns unstable.

"The bricks in the foundation of Yuanying Guan have disappeared, exposing the earth," Liu said. "Thick vegetation is another threat."

Some foundations have collapsed. Liu said that if this situation continues, the stone columns themselves, no longer adequately supported, will be in danger.

According to Qin Hai, an engineer at Tsinghua University's Architectural Design and Research Institute, the original foundation will be restored.

"Traditional skills will be used in renovation," he said.

The bricks, for instance, are made of earth, sand, sticky rice, and lime.

A new drainage system will be designed for the site to minimize the impact of rain, but the principle of minimum intervention will be followed for all cultural relics, he added.

Liu, the planning director, said further laboratory analysis is needed to decide whether to take additional measures to repair the upright columns in the next phase of work.

Yuanying Guan was a villa that belonged to one of Qianlong's favorite concubines.

According to historical records, it featured 1,206 pieces of colored glass, which are depicted in Western paintings.

As most wooden architecture in Yuanmingyuan was burned during the military vandalization in 1860, the surviving stone components of Yuanying Guan have become the most recognizable icons of Yuanmingyuan for Chinese people.

For a long time, the style of the ruins gave the general public an incorrect impression that Yuanmingyuan was a European-style garden. However, large-scale archaeological excavations all over Yuanmingyuan in recent years have gradually unveiled a panoramic facade from underground.

"Everyone sees Yuanying Guan in their school textbooks," Liu said. "It is also used as the logo of our park. Its cultural and historical significance is great, although it represents only a very small part of Yuanmingyuan.

"What we're doing is prevent potential hazards in the future. If the columns really collapsed, the loss would be irreversible."

The area will not be closed during the renovation, he said.