There is a story about Tongwan City within the territory of Wushen Banner of Ordos City. Elianbobo, king of the Great Xia Kingdom, has a talented elder sister, who could make soldiers by scattering beans. She helped his younger brother build Tongwan City and paved an 800-li-long Zhuanbing Cave under the city that could lead to Yan'an. After that, she lived in Yan'an. Upon her departure, she told her younger brother: "if enemy attacked you, you can knock the bronzebell that hangs in front of the cave's mouth three times and Iwill send soldiers to you."
Helianbobo was suspicious and thought that his elder sister was playing tricks on him. Once day, he knocked the bell suddenly. Later, thousands of tens of thousands of horsesand soldiers came to the cave's mouth and covered the field on bothsides of the Wuding River. When seeing it, Helianbobo laughed and said: "Haha, I am playing! What are you doing here?"
Several years later, enemies surrounded Tongwan City. Helianbobo became flusteredandknocked the bell in a hurry. However, his elder sister didn't send any soldiers to him. Several days later, the city was takenover by the enemies and Helianbobo became a captive.