Wu Zetian used her power to increase or to attempt to increase her power by manipulating Buddhist, Daoist, and Confucianist practice, sometimes in reference to the idea of the Mandate of Heaven. There are also allegations of witchcraft or sorcery. Wu began to manipulate the symbolic aspects of religious and imperial power long before she became huangdi, one case being the Sacrifice on Mount Tai, in 666. When Emperor Gaozong offered sacrifices to the deities of heaven and earth at Mount Tai, Empress Wu, in an unprecedented action, offered sacrifices after him, with Princess Dowager Yan, mother of Emperor Gaozong's brother Li Zhen, Prince of Yue, offering sacrifices after her. Wu Zetian's procession of ladies up Mount Tai conspicuously linked Wu with the most sacred traditional rites of the Chinese empire.