In 788 he built a small temple on the mountain and named it Hieisan-ji (Temple of Mount Hiei). (After Dengyō’s death, Emperor Saga renamed it Enryaku-ji in 823.) In 802, at age thirty-six, Dengyō was invited to Kyoto by the brothers and court nobles Wake no Hiroyo and Wake no Matsuna to lecture at their family temple, Takao-dera. There he expounded T’ien-t’ai’s three major works to eminent priests representing the seven major temples of Nara. This event catapulted Dengyō to prominence, winning him the support of Emperor Kammu, and greatly enhanced the prestige of the T’ien-t’ai doctrine.
In 804, accompanied by his disciple Gishin who acted as interpreter, Dengyō went to China. After making a pilgrimage to Mount T’ien-t’ai, the center of the T’ien-t’ai school, they stayed in the province of T’ai-chou, where the center was located. There Dengyō received the essentials of T’ien-t’ai Buddhism from Miao-lo’s disciple Tao-sui and then from Hsing-man, another disciple of Miao-lo. He also received the bodhisattva precepts, or those of perfect and immediate enlightenment, from Tao-sui, the Zen teachings from Hsiao-jan, and the anointment of Esoteric Buddhism from Shun-hsiao. In 805 he returned to Japan and the next year established the Tendai school. In those days, all Buddhist priests were ordained exclusively in the Hinayana precepts. Dengyō wished to ordain his disciples with Mahayana precepts and made continual efforts to obtain imperial permission for the building of a Mahayana ordination center on Mount Hiei in the face of determined opposition from the older schools of Nara. Permission was finally granted a week after Dengyō’s death in 822, and in 827 his successor Gishin completed the ordination center.
After his return to Japan, in addition to this project, Dengyō concentrated his efforts on refuting the doctrines of the older Buddhist schools. In particular, his ongoing debate with Tokuitsu, a priest of the Dharma Characteristics (Hossō) school, is well known. That debate began in the early Kōnin era (810–824). Tokuitsu asserted that the one vehicle teaching of the Lotus Sutra was a provisional teaching that Shakyamuni Buddha expounded in accordance with the people’s capacity, while the three vehicle teachings were true teachings, and that there are some people who are without the potential to attain Buddhahood. In opposition to this assertion, Dengyō maintained that all people have the Buddha nature, and that the one vehicle of Buddhahood expounded in the Lotus Sutra is the true teaching.
Among Dengyō’s major disciples were Gishin, Enchō, Kōjō, Jikaku, Chishō, and Ninchū. His works include The Outstanding Principles of the Lotus Sutra, A Clarification of the Precepts, An Essay on the Protection of the Nation, and The Regulations for Students of the Mountain School.
