In the Eastern Han Dynasty (A.D. 25-220), a group of Taoist philosophers created Yin Taoism, firmly rooted in the importance of human sexual expression. This school of Taoists wrote volume after volume of sex manuals including "Su Nu Ching" (Manual of Lady Purity), "Yu Fang Mi Chueh" (Secret Codes of the Jade Room) the "Art of the Bedchamber" and "Yu Fang Chih Yao" (Important Guidelines of the Jade Room). To give their works authority and to exert influence on the emperors the Yin Taoists attributed the key points in their manuals to Huang Ti (the Yellow Emperor) and the ancient authority Peng Tsu who was said to have lived to 800 years of age.