If you thought the 8,000 terra cotta warriors were the last archeological surprise this ancient capital of China had in store, think again. The more than 2-millennia-old tomb of China's first emperor Qinshihuang has thrown up yet another secret: a 30-meter-tall building. The building, buried in the main part of the 51-meter-high pyramid-like tomb, has four walls, each with nine steps or platforms, says Duan Qingbo, a researcher with the Shaanxi Institute of Archaeology. Duan is part of the expert group that has been studying the tomb and its adjoining areas for five years. But since the entire building is still buried, the researchers are finding it difficult to get its complete picture and purpose. They have to depend on remote sensing technology because no excavation at the site is allowed, Duan says. The building, however, might have been built as a "chamber for the emperor's soul", he says. The Terra Cotta Warriors were discovered accidentally by some farmers in 1974 when they were digging a well in the capital of Northwest China's Shaanxi Province. Excavation later revealed the first batch of 1,500 warriors and horses "guarding the soul" of Emperor Qinshihuang. He became China's first emperor in 221 BC after unifying the country.