[1] According to family tradition, Saichō's ancestors were descendants of emperors of Eastern Han China;[1] however, no positive evidence exists for this claim.

Gyōhyō in turn was a disciple of Dao-xuan (702–760, 道璿, Dōsen in Japanese), a prominent monk from China[5] of the Tiantai school who had brought the East Mountain Teaching of Chan Buddhism, Huayan teachings and the Bodhisattva Precepts of the Brahmajala Sutra to Japan in 736 and served as the "precept master" for ordination prior to the arrival of Jianzhen.

A few months later he abruptly retreated to Mount Hiei for an intensive study and practice of Buddhism, though the exact reason for his departure remains unknown.

Because Mount Hiei was coincidentally located to the northeast of Kyoto, a direction considered dangerous according to Chinese geomancy, Saichō's presence on the mountain was thought to protect the new capital and brought him to the attention of the court.

During this time, Saichō likely met another passenger, Kūkai, a fellow Buddhist monk who was sent to China on a similar mission though he was expected to stay much longer.

The Tiantai school originally only utilized "mixed" (zōmitsu (雑密)) ceremonial practices, but over time esoteric Buddhism took on a greater role.

This edict states that, following Saichō's request, the ordinands would be divided between two curricula: the shanagō course, centering on the study of the Mahavairocana Sūtra (this was the Mikkyō curriculum, shana being the abbreviation for Birushana, the Japanese transliteration of Vairocana), and the shikangō course, based on the study of the Mo-ho chih-kuan, the seminal work of the T'ien-t'ai patriarch Chih-i 智顗 (538–597) (this was the Tendai curriculum, shikan being the Japanese reading of Chih-i's central practice of chih-kuan [cessation and contemplation]) (Kenkairon engi, DZ 1, pp. 294–296).

It was as a subdivision of Saichō's new school that Mikkyō first received the official acknowledgment of the imperial court and became a proper subject of study in Japanese Buddhism.

[7] By 822, Saichō petitioned the court to allow the monks at Mount Hiei to ordain under the Bodhisattva Precepts rather than the traditional ordination system of the prātimokṣa, arguing that his community would be a purely Mahayana, not Hinayana one.

During the last month of his stay on Chinese soil, while awaiting the arrival of his ship at the port city of Ming-chou, Saichō traveled to Yüeh-chou to collect additional Buddhist texts.

At Lung-hsing ssu 龍興寺 Saichō chanced to meet the priest Shun-hsiao"[7], and likewise returned with esoteric (tantric) Buddhist texts.

Saichō 最澄 and Kūkai 空海 are renowned as the founders, respectively, of the Japanese Tendai and Shingon schools, both of which grew into influential institutions of continuing importance even today.

Saichō, for example, prepared the way for Kūkai—still largely unrecognized after his return from T'ang China—to perform the Mikkyō initiation ritual of abhiṣeka (kanjō 灌頂) for the high priests of the Nara Buddhist establishment and the dignitaries of the imperial" Heian court.

Many of them defected to the Hosso school; others departed in order to study Esoteric Buddhism with Kūkai or to support their ailing mothers.

[13]Moreover, Saichō began to realize that his own idea of "enmitsu itchi" was not exactly shared by the esoteric Shingon school, and especially its founder Kūkai (Kōbō Daishi).

Ryuichi Abe writes, [W]hat makes the relationship between Saichō and Kūkai decisive in Japanese Buddhist history is not so much their cooperation as the manner in which it came to an end.

Their alliance began to deteriorate when Saichō, after receiving abhiseka from Kūkai, hurried back to Mount Hiei, where the work of laying the foundation of the new Tendai school awaited him.

The break between Saichō and Kūkai left a long-lasting legacy in the Tendai and Shingon schools, whose complex relationship, constantly oscillating between affiliation and rivalry, shaped the contours of Buddhist history in the Heian period.

[7]During the last five or six years of his life, Saicho strove to secure the place of Tendai within Japanese Buddhism, and in the process composed almost all of his major works.

"[7]Saichō's late life criticisms were ignored by his own leading disciples, and the Tendai would continue to teach Mikkyō and Shikangō (śamatha-vipaśyanā).