Yi Xing

Yixing (, 683–727) was a Buddhist monk of the Tang dynasty, recognized for his accomplishments as an astronomer, a reformer of the calendar system, a specialist in the ''Yijing'' (易經), and a distinguished Buddhist figure with expertise in Esoteric Buddhism.Kotyk
Yixing一行 (673/683–727), Brill's Encyclopedia of Buddhism Volume II
BRILL 2019

In the realm of secular affairs, Yixing gained prominence for his reforms to the imperial calendar and his construction of a celestial globe featuring a liquid-driven escapement, the first in a long tradition of Chinese astronomical clockworks. Within Buddhist circles, he is particularly remembered for his contributions to the translation of the '' Mahāvairocana-sūtra'' and for authoring the authoritative commentary on that scripture, the ''Darijing shu'' 大日經疏 (T 1796). Due to his significant activities in both religious and secular spheres, a legendary portrayal of Yixing as a master astrologer and practitioner of astral magic developed during the late Tang period, leading to the attribution of several astrological works to him.

Life

Originally named Zhang Sui (張遂), Yixing (一行), was born in Changle, Weizhou (modern Nanle in Hebei) though other sources suggest his birthplace was Julu, present-day Pingxiang, Hebei. A great-grandson of the Tang dynasty statesman Zhang Gongjin (張公謹; 584–632), Yixing came from a distinguished family, possibly influencing his later connection to the Tang court. His early intelligence was recognized in the ''Jiu Tang shu'', which records his precocious mastery of classical texts, particularly in astronomy, calendrical science, and traditional Chinese philosophy. After the deaths of his parents at age 21, Yixing renounced secular life and was ordained as a Buddhist monk. He trained under several masters, including Hongjing and Facheng, and later under Puji at Mount Song, receiving transmission within the Northern Chan lineage. His deep cultivation of "single-practice samādhi" (一行三昧) led to his monastic name, and there is evidence suggesting he was also a disciple of Shenxiu. Throughout his early career, Yixing displayed exceptional devotion to the study of the Vinaya, and he composed a now-lost treatise on Vinaya essentials.

During the early eighth century, Yixing avoided political entanglement with powerful figures such as Wu Sansi, choosing instead a life of itinerancy, seeking Buddhist instruction throughout the southern regions. He studied the "Indian Vinaya" under Wuzhen at Mount Dangyang and received additional teachings from the monk Daoyi. In 717, Emperor Xuanzong personally summoned Yixing to the capital, where he became an esteemed religious advisor, frequently consulted on matters of governance and the welfare of the people. Yixing spent his final years primarily in Chang'an and Luoyang, focusing on religious activities. In 727, after a period of illness during which extensive merit-making ceremonies were performed for his recovery, Yixing died while traveling with the emperor. Xuanzong composed the inscription for his memorial stele, and posthumously conferred upon him the title Meditation Master Dahui (大慧禪師).

Yixing’s most significant contributions during his later life centered around his involvement in the translation and interpretation of Esoteric Buddhist texts. He collaborated with the Indian master Śubhakarasiṃha in translating the '' Mahāvairocana-sūtra'', working primarily as an editor and recorder rather than as a direct translator, suggesting limited proficiency in Sanskrit. The surviving Chinese translation condenses the much larger Sanskrit original. Yixing also compiled an influential commentary on the ''Mahāvairocana-sūtra'', preserving Śubhakarasiṃha’s oral teachings while incorporating his own notes and references to Chinese Buddhist sources. Two versions of this commentary survive, the ''Dari jing shu'' (大日經疏) and the ''Dari jing yishi'' (大日經義釋). The work reflects a synthesis of Esoteric Buddhist thought with elements of Huayan philosophy and cites seminal texts such as Nāgārjuna’s ''Madhyamaka-śāstra'' and the '' Da zhidu lun''.

In addition to his work with Śubhakarasiṃha, Yixing is also reported to have studied under Vajrabodhi, from whom he received the Vajraśekhara abhiṣeka initiation and whom he assisted in translation efforts. His literary contributions extend beyond Esoteric Buddhism; the ''Jiu Tang shu'' lists a lost work titled ''Shishi xilu'' (釋氏系錄), which appears to have covered a wide range of monastic regulations and practices. Yixing's legacy, while celebrated for his astronomical and calendrical reforms in secular histories, is equally significant in the Buddhist tradition for his pioneering role in the early transmission of Esoteric Buddhism to China.

Legends

Yixing’s prominence gave rise to many legendary narratives about him. Japanese sources recount that when Yixing’s mother was pregnant, a halo of white light appeared on her forehead, later transferring to the newborn Yixing. Stories portraying him as an extraordinary figure also circulated in Tang dynasty literature, indicating his influence beyond Buddhist circles. Notably, texts like the ''Kaitian chuanxin ji'', ''Minghuang zalu buyi'', and ''Youyang zazu'' record anecdotes of Yixing appearing as a spirit and bearing the Daoist title "Heavenly Master." Moreover, the ''Jiu Tang shu'' describes Yixing’s encounter with a Daoist named Yin Chong, from whom he borrowed the ''Taixuan jing''. Demonstrating rapid mastery of its profound teachings, Yixing impressed Yin Chong by producing new scholarly works. Such tales, while celebrating Yixing’s intellect, are likely hagiographical embellishments intended to bolster his reputation.

Another account details Yixing’s search for instruction in the ''Yijing''’s number theory, eventually leading him to Guoqing Temple on Mount Tiantai. According to legend, he was foretold by a monk within the temple and miraculously admitted when the waters outside reversed their flow, symbolizing his destined arrival. Although framed within Buddhist texts like the ''Song Gaoseng zhuan'', this story is more connected to mathematical traditions than Buddhist practice. In the late Tang, as foreign astrology gained prominence and astral magic merged into both Buddhism and Daoism, Yixing’s image evolved further. He became associated with esoteric rites involving stellar deities, such as summoning the gods of the 28 lunar stations, as recorded in the ''Qiyao xingchen bie xingfa''. These accounts, blending elements of Mantrayāna and astrology, reflect a mythologized view of Yixing shaped by the cultural and religious currents of the time.

Astronomical work

Astrogeodetic survey

In the early 8th century, the Tang court put Yi Xing in charge of an astrogeodetic survey.Hsu, 98. This survey had many purposes. It was established in order to obtain new astronomical data that would aid in the prediction of solar eclipses. The survey was also initiated so that flaws in the calendar system could be corrected and a new, updated calendar installed in its place.

The survey was also essential in determining the arc measurement, i.e., the length of meridian arc-although Yi Xing, who did not know the Earth was spherical, did not conceptualize his measurements in these terms. This would resolve the confusion created by the earlier practice of using the difference between shadow lengths of the sun observed at the same time at two places to determine the ground distance between them.

Yi Xing had thirteen test sites established throughout the empire, extending from Jiaozhou in Vietnam — at latitude 17°N — to the region immediately south of Lake Baikal — latitude 50°N.Hsu, 99. There were three observations done for each site, one for the height of polaris, one for the shadow lengths of summer, and one for the shadow lengths of winter. The latitudes were determined from this data, while the Tang calculation for the length of one degree of meridian was fairly accurate compared to modern calculations. Yi Xing understood the variations in the length of a degree of meridian, and criticized earlier scholars who permanently fixed an estimate for shadow lengths for the duration of the entire year.

The escapement and celestial globe

Yi Xing was famed for his genius, known to have calculated the number of possible positions on a go board game (though without a symbol for zero as he had difficulties expressing the number). He, along with his associate, the mechanical engineer and politician Liang Lingzan, is best known for applying the earliest-known escapement mechanism to a water-powered celestial globe.Needham, Volume 3, 351. However, Yi Xing's mechanical achievements were built upon the knowledge and efforts of previous Chinese mechanical engineers, such as the statesman and master of gear systems Zhang Heng (78–139) of the Han dynasty, the mechanical engineer Ma Jun (200–265) of the Three Kingdoms, and the Daoist Li Lan (c. 450) of the Southern and Northern Dynasties period.

It was the earlier Chinese inventor Zhang Heng during the Han dynasty who was the first to apply hydraulic power (i.e. a waterwheel and water clock) in mechanically-driving and rotating his equatorial armillary sphere. The arrangement followed the model of a water-wheel using the drip of a clepsydra (see water clock), which ultimately exerted force on a lug to rotate toothed-gears on a polar-axis shaft.Needham, Volume 4, 532. With this, the slow computational movement rotated the armillary sphere according to the recorded movements of the planets and stars. Yi Xing also owed much to the scholarly followers of Ma Jun, who had employed horizontal jack-wheels and other mechanical toys worked by waterwheels. The Daoist Li Lan was an expert at working with water clocks, creating steelyard balances for weighing water that was used in the tank of the clepsydra, providing more inspiration for Yi Xing. Like the earlier water-power employed by Zhang Heng and the later escapement mechanism in the astronomical clock tower engineered and erected by Su Song (1020–1101), Yi Xing's celestial globe employed water-power in order for it to rotate and function properly.Needham, Volume 4, 470.Joseph Needham, ''Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2: Mechanical Engineering'' (Taipei: Caves Books, Ltd. 1986) pp. 470–475.

The British biochemist, historian, and sinologist Joseph Needham states (Wade–Giles spelling):

In regards to mercury instead of water (as noted in the quote above), the first to apply liquid mercury for motive power of an armillary sphere was Zhang Sixun in 979 AD (because mercury would not freeze during winter).Needham, Volume 3, 350.Needham, Volume 4, 471. During his age, the Song dynasty (960–1279) era historical text of the ''Song Shi'' mentions Yi Xing and the reason why his armillary sphere did not survive the ages after the Tang (Wade–Giles spelling):

Earlier Tang era historical texts of the 9th century have this to say of Yi Xing's work in astronomical instruments in the 8th century (Wade–Giles spelling):

Buddhist scholarship

Yi Xing wrote a commentary on the '' Mahavairocana Tantra''. This work had a strong influence on the Japanese monk Kūkai and was key in his establishment of Shingon Buddhism.Rethinking Japan p.330

In his honor

At the Tiantai-Buddhist Guoqing Temple of Mount Tiantai in Zhejiang Province, there is a Chinese pagoda erected directly outside the temple known as the Memorial Pagoda of Monk Yi Xing. His tomb is also located on Mount Tiantai.

See also

* List of Chinese people
* List of inventors
* List of mechanical engineers
*Verge escapement
* Villard de Honnecourt

Notes

References

*
*Bowman, John S. (2000). ''Columbia Chronologies of Asian History and Culture''. New York: Columbia University Press.
*Fry, Tony (2001). ''The Architectural Theory Review: Archineering in Chinatime''. Sydney: University of Sydney Press.
*Ju, Zan
"Yixing"
'' Encyclopedia of China'' (Religion Edition), 1st ed.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 3''. Taipei: Caves Books, Ltd.
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 4, Part 2''. Taipei: Caves Books, Ltd.
*Boscaro, Adriana (2003) ''Rethinking Japan: Social Sciences, Ideology and Thought''. Routledge. 0-904404-79-x p. 330

External links

Yi Xing at Chinaculture.org

{{DEFAULTSORT:Yi, Xing
683 births
727 deaths
8th-century Buddhists
8th-century Buddhist monks
8th-century Chinese astronomers
8th-century Chinese philosophers
8th-century Chinese writers
8th-century engineers
8th-century inventors
category:8th-century mathematicians
Astronomical instrument makers
Chinese Buddhists
Chinese inventors
Chinese mechanical engineers
Chinese scholars of Buddhism
Chinese science writers
Chinese scientific instrument makers
Engineers from Henan
Hydraulic engineers
Mathematicians from Henan
Mathematicians from Imperial China
Philosophers from Henan
Tang dynasty Buddhist monks
Tang dynasty philosophers
Technical writers
Writers from Puyang