Chinese archaeologists said underground passages in the ruins of an ancient Chinese capital near Xi'an might have been dug during complex power struggles in the Han Dynasty 2,200 years ago.

"The underground passages are the first ever discovered in the ruins of an ancient Chinese capital," said Liu Qingzhu, a researcher with the Chinese Institute of Archaeology in the Chinese Academy of Social Sciences (CASS).

"The tunnels were mostly discovered under the palaces where the royal women lived, including the emperor's mother, the empress and the emperor's concubines," Liu said.

Historical records show the emperors in the Western Han Dynasty (206 BC - 25 AD) relied partly on the families of the imperial females to consolidate their rule.

"The emperors had many concubines, some of whom were chosen for political reasons to consolidate royal power through their families," Liu said. "The political groups might have used the tunnels to meet secretly in various palaces in the capital."

"The underground passages are very intricate. Some had gatekeepers to control who went in and who went out," Liu said.

The ruins of nearly 20 underground passages have been discovered and some stretch for about 20 meters, according to Zhang Jianfeng, an archaeologist with the Chinese Institute of Archeology in the CASS.

Many other discoveries were made under the palaces.

"Some of the basements may have been used for residence, storage or preserving the upper floors from humidity or cold, but we need more evidence," Zhang said.

The Western Han Dynasty ruled for about 200 years from its capital in Xi'an.

The imperial capital covered an area of about 36 square kilometers. The main palace, Weiyang Palace, covered about five square kilometers. It was the largest palace in ancient China, much larger than the famous Forbidden City.

The Western Han Dynasty was one of the most prosperous periods in ancient Chinese history. Its capital Chang'an, today's Xi'an, in northwestern Shaanxi Province, once competed with Rome as the most important metropolis in the known world.

(Xinhua News Agency November 2, 2006)