A mask of pure gold is just one fifth of a millimeter thick. The craftsmanship of relics discovered at the Sanxingdui archaeological site in southwest China's Sichuan Province, even by modern standards, is highly advanced. The gilding technique was far ahead of its time, and no one knows how the ancient Shu people, over 3,000 years ago, could master it. An archaeological expert believes such exquisitely crafted masks represent senior shamans.