In the fourth year of the Chuigong era of Empress Wu Zetian's reign (688).
To curry favor with Wu Zetian, Wu Chengsi ordered someone to carve the eight characters “The Sacred Mother has come to rule; the imperial enterprise shall flourish forever” into a stone and paint them red. He then had Tang Tongtai pretend to have found it in the Luo River and present it to Wu Zetian. Delighted, she went in person to the southern outskirts to offer thanks to Heaven's protection and held a ceremony to worship the Luo River and receive the auspicious sign. She named the stone the Heavenly Mandate's Sacred Diagram, renamed the Luo River the River of Eternal Prosperity, and bestowed the title Marquis of Manifest Divinity upon its river god.
Afterward, Wu Zetian received her officials in the Hall of Light and adopted the title Sacred Mother Divine Empress. To mark the auspicious sign, she ordered the governors and prefects of every province, members of the imperial clan, and her maternal relatives to gather in the divine capital ten days before the ceremony and accompany her to receive the diagram.
At the time, rumors were rife among the people that Wu Zetian intended to usurp the throne, and that she had summoned members of the imperial clan under the pretext of receiving the diagram from the Luo River so she could massacre them.
The ceremony strengthened Wu Zetian's position, but also made her relationship with the imperial clan increasingly complicated. To weaken her influence, rumors of supernatural creatures began to spread among the people, and strange events occurred across the land. In order to “prove Heaven's mandate with auspicious signs” and ensure the success of her coronation, Wu Zetian secretly established the Mirror Mystery Bureau to investigate supernatural forces.
