During the Pre-Qin Dynasty, a comet fell from the sky: wherever the comet landed, everything floated in the sky. When the First Emperor learned of this, he ordered three thousand soldiers to spend a year to collect him in Afang Palace. He also killed thousands of local people and falsely claimed that he was guilty of rebellion. After obtaining the gem, the First Emperor summoned thousands of craftsmen to build a wooden castle, which was made up of a thousand rooms. He then placed the gem in the castle. The castle immediately floated in the air and was tied to Xianyang with several iron chains. It was repaired several times. The First Emperor collapsed, and the Second Emperor succeeded to the throne. The world was in chaos. Liu Bang led his troops to attack Xianyang. The Second Emperor lied about the rebellion and led his ministers and concubines to escape from the city. After Qin died, the descendants of Qin Dynasty only left the city in the world. From then on, the city floated in the air and was isolated from the world. Over time, this matter was forgotten by the world, and few people knew about it.