Zhang Tian'en, an expert with the Shaanxi Provincial Archaeology Institute, told Xinhua on Saturday that the tomb was chronologically the closest to the mysterious mausoleum of Qinshihuang, and was probably built on the emperor's orders.

    "We are hoping that the excavation of his grandmother's tomb will help unravel the mystery about the first emperor's mausoleum, which still cannot be excavated. It will also contribute to research into Qin Dynasty burial culture," Zhang said.

    The tomb, located in the southern outskirts of Xi'an, provincial capital of Shaanxi, is the second largest ancient tomb excavated in China. Only the tomb of King Jinggong of the State of Qin (897-221 BC) is bigger, said Zhang.

    Located under the new campus of the Xi'an Business College, the tomb is about 30 kilometers southwest of Qinshihuang's famous mausoleum. Qinshihuang united seven warring states and founded the Qin Dynasty in 221 BC.

    550 meters long and 310 meters wide, the tomb covers an area of 17.3 hectares.

    Archaeologists unearthed two carriages designed to be driven by six horses, which could only be used by kings and queens in the State of Qin.

    The seals of court officials responsible for running errands on behalf of queens, queen mothers and princes, have also been found, said Wang Hui, an expert with Shaanxi Normal University.

    After further examination on the unearthed articles and comparisons with Qin mausoleums, the archaeologists concluded that the tomb belonged to Qinshihuang's grandmother, Queen Mother Xia.

    According to Ding Yan, an associate researcher with the Shaanxi Research Institute of Cultural Relics and Archaeology, the main tomb for the Queen Mother is 140 meters long, 113 meters wide and 15 meters deep, with the tomb chamber covering an area of more than 100 square meters.

    Ding said that since the tomb was raided and burned several times, only fragments of Qin coins, grey clay vases and red clay boilers have been unearthed, as well as shards of decorative and ritual jade objects, broken pottery and pieces of bronze.

    Sadly, Qingshihuang's grandmother's inner and outer coffins were also burned, Ding added.

    The tomb is still under excavation.

    Zhang Tian'en said that the Queen Mother lived until Qinshihuang was 20 years of age and in the seventh year of his reign. The royal lady is believed to have exerted considerable influence on the politics of the later years of the State of Qin and on Qinshihuang in particular.

    China's survey of the 2,200-year-old Qinshihuang mausoleum has lasted nearly 40 years. What has been discovered is believed to be just the tip of the iceberg.

    The site remains a mystery even if the terra cotta warrior underground army has long been unearthed and hailed as the world's eighth wonder.

    "The best choice is to leave the ancient tomb untouched because, given the complicated conditions inside, excavation errors could lead to its destruction," said Duan Qingbo, a top archaeologist with the Shaanxi Provincial Archaeology Institute.

    "Current techniques cannot ensure that the mausoleum will be properly protected after excavation."

    According to historical records, some 720,000 workers labored 38 years to build the mausoleum for the emperor, who ruled the Qin Dynasty, China's first unified dynasty, from 221-206 BC.

    Archaeologists, using remote sensing equipment, have located symmetrical staircases leading down into the tomb and wooden structures inside the tomb.

    They have also discovered that the tomb was built with an effective drainage system that has prevented ground water from seeping inside, according to Duan.

    Legends maintain that a huge underground palace was modeled on the emperor's realm with rivers flowing with mercury and the ceiling studded with pearls and diamonds representing the stars and sun.

    "Our survey shows that the mercury density in Qinshihuang's cemetery area is vastly higher than that in the surrounding area, and confirms that the mercury comes from the mausoleum," Duan said.

    The mausoleum was also said to have architectural designs that archaeologists believe have successfully kept out tomb robbers. Enditem