 It was during his period at Takaosan-ji that he wrote some of his major treatises of philosophical interest to us, such as Benkenmitsu nikkyōron (Treatise on the Differences Between Esoteric and Exoteric Teachings) around 814, and the so-called Sanbu-sho (“Three Writings”) of Sokushinjōbutsugi (On the Meaning of “Attaining Buddhahood in this Very Embodied Existence”), Shōjijissōgi (On the Meanings of “Sound, Sign, and Reality”), and Unjigi (On the Meaning of the Syllable Hūṃ) in the 820s. And towards the end of his life he completed in 830 what has been considered to be his magnum opus, the Himitsu mandara jūjūshinron (Treatise on the Ten States of the Mind as a Secret Mandala) in ten volumes, and soon afterward, completed its summary version, the Hizō hōyaku (The Precious Key to the Secret Treasury) in three volumes. 