XI'AN, June 15 (Xinhua) -- An ancient Chinese city
wall with a history of more than 14 centuries is being eaten away by a kind of
mite in Xi'an, capital of northwestern Shaanxi Province, archaeologists have
Experts were surprised to find it had been the mites
undermining the wall at the Hanguang Entrance Remains Museum during their
one-year research for further protection.
"The discovery is the world's first of this kind. The
mites had damaged the wall seriously," said Li Yuhu, archaeologist of Shaanxi
The Hanguang Entrance is one of the 18 entrances in
the city wall in Xi'an, which served as the nation's capital for 13 dynasties in
history. The eight-meter-high entrance with three gates, one 5.5-meter-wide gate
in the middle and two 5.3-meter-wide gates in the east and west, is the best
preserved one, and was built at the beginning of the seventh century.
The wall had created a suitable environment for
bacteria which feeds mites, Li said.
The mites had lived and built their dens in the wall
for a thousand years, and had eaten it away from the inside, Li said.
Li and his colleagues have begun killing the mites
with insecticide, by transfusing and spraying the pollution-free chemical into
the wall once every 20 days. "The insecticide is widely used across the world
and has proven harmless to human being, vegetation and the environment," said
Because of its involatile nature, its effect could
last seven to 14 years, he said.
Meanwhile, experts have also developed a kind of
material to reinforce the wall against a number of other mite-related problems,
including bacteria, loosening and cracks, Li said.
The material, invented by Li in 1990, had proven to
be effective in the protection of the terracotta warriors and Banpo Ruins in the
province during the last decade, Li said.
A protection team set up last year has carried out a
one-year study on Li's protection method and tried to figure out a way to
improve the method exclusively for the wall, said Wang Su, head of the
protection bureau of the Hanguang Entrance Remains Museum.
The experts tested the method on the earth floor from
the Tang Dynasty (618-907) before using it on the real wall, which proved
effective, said Wang Danhu, an expert with the technological section of the
State Administration of Cultural Heritage.
The new material made the earth stronger and more
permeable, Wang said.
If successful, the method will have a broad future as
most of China's historic buildings were built using earth, which had been a
difficult problem for the world's archaeologists, An Jiayao, archaeologist of
Institute of Archaeology, Chinese Academy of Social Sciences.
Relics in Japan and the Republic of Korea also face
the same problem, An said.
"It is just the beginning. We know very little about
the mites and we want to further investigate them," Li Yuhu said.