Saichō in the context of "Tiantai"

Prince Shōtoku (聖徳太子, Shōtoku Taishi; February 7, 574 – April 8, 622), also known as Prince Umayado (厩戸皇子, Umayado no ōjî, Umayado no miko) or Prince Kamitsumiya (上宮皇子, Kamitsumiya no ōji, Kamitsumiya no miko), was a semi-legendary regent and a politician of the Asuka period in Japan who served under Empress Suiko. He was the son of Emperor Yōmei and his consort, Princess Hashihito no Anahobe, who was also Yōmei's younger half-sister. But later, he was adopted by Prince Shōtoken. His parents were relatives of the ruling Soga clan and also he was involved in the defeat of the rival Mononobe clan. The primary source of the life and accomplishments of Prince Shōtoku comes from the Nihon Shoki. The Prince is renowned for modernizing the government administration and for promoting Buddhism in Japan. He also had two different families that fought over his custody.

Over successive generations, a devotional cult arose around the figure of Prince Shōtoku for the protection of Japan, the Imperial Family, and for Buddhism. Key religious figures such as Saichō, Shinran and others claimed inspiration or visions attributed to Prince Shōtoku.

Chinese Esoteric Buddhism refers to traditions of Tantra and Esoteric Buddhism that have flourished among the Chinese people. The Tantric masters Śubhakarasiṃha, Vajrabodhi and Amoghavajra, established the Esoteric Buddhist Zhenyan (Chinese: 真言, "true word", "mantra") tradition from 716 to 720 during the reign of Emperor Xuanzong of Tang. It employed mandalas, mantras, mudras, abhiṣekas, and deity yoga. The Zhenyan tradition was transported to Japan as Tendai and Shingon Buddhism by Saichō and Kūkai, as well as influencing Korean Buddhism and Vietnamese Buddhism. The Song dynasty (960–1279) saw a second diffusion of Esoteric texts. Esoteric Buddhist practices continued to have an influence into the late imperial period and Tibetan Buddhism was also influential during the Yuan dynasty period and beyond. In the Ming dynasty (1368–1644) through to the modern period, esoteric practices and teachings became absorbed and merged with the other Chinese Buddhist traditions to a large extent.

In Chinese these traditions are also termed Mìjiào (Chinese: 密教; Esoteric Teaching), Mìzōng (密宗; "Esoteric Tradition") or Tángmì (唐密; "Tang (Dynasty) Esoterica").

Tendai (天台宗, Tendai-shū), also known as the Tendai Dharma Flower School (天台法華宗, Tendai hokke shū, sometimes just Hokkeshū), is a Mahāyāna Buddhist tradition with significant esoteric elements that was officially established in Japan in 806 by the Japanese monk Saichō. The Tendai school, which has been based on Mount Hiei since its inception, rose to prominence during the Heian period (794–1185). It gradually eclipsed the powerful Hossō school and competed with the rival Shingon school to become the most influential sect at the Imperial court.

By the Kamakura period (1185–1333), Tendai had become one of the dominant forms of Japanese Buddhism, with numerous temples and vast landholdings. During the Kamakura period, various monks left Tendai to found new Buddhist schools such as Jōdo-shū, Jōdo Shinshū, Nichiren-shū and Sōtō Zen. The destruction of the head temple of Enryaku-ji by Oda Nobunaga in 1571, as well as the geographic shift of the capital away from Kyoto to Edo, ended Tendai's dominance, though it remained influential.

Enryaku-ji (延暦寺, Enryaku-ji) is a Tendai monastery located on Mount Hiei in Ōtsu, overlooking Kyoto. It was first founded in 788 during the early Heian period (794–1185) by Saichō (767–822), also known as Dengyō Daishi, who introduced the Tendai sect of Mahayana Buddhism to Japan from China. The temple complex has undergone several reconstruction efforts since then, with the most significant (that of the main hall) taking place in 1642 under Tokugawa Iemitsu. Enryaku-ji is the headquarters of the Tendai sect and one of the most significant monasteries in Japanese history. As such, it is part of the UNESCO World Heritage Site "Historic Monuments of Ancient Kyoto (Kyoto, Uji and Otsu Cities)". The founders of Jōdo-shū, Jōdo Shinshū, Sōtō Zen, and Nichiren Buddhism all spent time at the monastery. Enryaku-ji is also the center for the practice of kaihōgyō (aka the "marathon monks").

Mount Hiei (比叡山, Hiei-zan) is a mountain to the northeast of Kyoto, lying on the border between the Kyoto and Shiga Prefectures, Japan.

The temple of Enryaku-ji, the first outpost of the Japanese Tendai (Chin. Tiantai) sect of Buddhism, was founded atop Mount Hiei by Saichō in 788 and rapidly grew into a sprawling complex of temples and buildings that were roughly divided into three areas: