Cai Lun

Cai Lun (蔡倫), courtesy name Jingzhong, was a eunuch official at the court of the Eastern Han dynasty (25–220 CE) in China. Chinese tradition has long honoured him as the inventor of paper. Modern historians describe his role more precisely: paper already existed before him, but he developed and presented an improved method that used new, cheaper raw materials and produced paper good enough for writing. His report to the throne in 105 CE is the first official record of papermaking in Chinese history.

Almost everything we know about him comes from a short biography of about three hundred Chinese characters in the Book of the Later Han, compiled in the fifth century from earlier Han records. It tells of his career, his skill as a craftsman-administrator, his involvement in palace politics and his dramatic death.

Although he lived nearly two thousand years ago, Cai Lun is still a well-known figure in China and beyond. He was worshipped as a patron god by papermakers, and modern lists of the most influential people in history often include him.

In early China, most writing was done on bamboo or wooden slips: thin strips, each holding a single column of characters, tied together with cords into rolls. Government records, letters, laws and books were all written this way. Slips were cheap to make but bulky and heavy. Wealthy people could write on silk, which was light and smooth but very expensive.

The Book of the Later Han puts the problem neatly: “Since ancient times, writings were mostly on bundled bamboo slips; those on silk were called zhi. Silk was costly and slips were heavy, so neither was convenient.” Interestingly, the word zhi, which today means paper, first referred to writing material made of silk.

Writing on slips shaped the whole culture of the scribe. A clerk kept a brush for writing and a small knife for scraping away mistakes from the wood or bamboo, which is why junior officials were sometimes called “knife-and-brush clerks”. A single long text needed hundreds or thousands of slips, and when the cords rotted the slips could fall out of order, causing confusion that later scholars still struggle to sort out. Sending a long report to the capital meant carrying a heavy load.

The Han empire was a huge bureaucratic state, with officials sending reports, registers and orders across thousands of kilometres. A light, cheap writing material that could be made in large quantities would change how information was stored and moved. This is the need that paper met.

According to his biography, Cai Lun “used tree bark, hemp ends, worn-out cloth and fishing nets to make paper”. All of these contain plant fibres. Hemp and ramie were used for cloth and ropes; the bark was probably the inner bark of trees such as the paper mulberry, whose long, strong fibres later became the classic material of East Asian paper.

The general process, known from later Chinese descriptions and from experiments with Han-period techniques, went like this. The raw materials were cut up, soaked in water, and boiled, probably with plant ash or lime, which helps break them down. Then they were pounded with mallets or in a mortar until the fibres separated into a pulp. The pulp was stirred into a vat of water. A worker dipped a screen stretched on a frame into the vat, or poured pulp onto it, and lifted it out so that the water drained through, leaving a thin, even mat of fibres. The sheet was pressed and dried in the sun or on a wall.

The key idea is that paper is not woven. Unlike cloth, it is made of countless tiny fibres that lock together as they dry. Recycled rags and nets were especially valuable because their fibres had already been processed, and using bark opened up a nearly unlimited supply.

Cai Lun came from Guiyang Commandery in the south, traditionally identified with modern Leiyang in Hunan. Nothing is known of his family; he was probably from a humble background. He entered palace service as a eunuch at the end of the Yongping era (58–75 CE) under Emperor Ming, and in the Jianchu era (76–84) under Emperor Zhang became a Junior Attendant of the Yellow Gates (xiao huangmen).

When the ten-year-old Emperor He came to the throne in 88 CE, Cai Lun was promoted to Regular Palace Attendant (zhongchang shi), the highest post reserved for eunuchs, and took part in confidential deliberations. His biography praises him as talented and learned, devoted and careful, often daring to criticize the emperor’s mistakes. On his days off he shut his door to visitors and went out to the fields.

He was also appointed Director of the Imperial Workshops (shangfang ling), which produced weapons, instruments and luxury goods for the palace. In 97 CE he supervised the making of swords and other implements that, the history says, were so finely made they became models for later generations. It was probably in this setting, with skilled artisans and materials at his disposal, that the improved papermaking method was developed. In 105 CE (the first year of Yuanxing) he presented it to Emperor He, who praised his ability, and from then on, the history says, it was used everywhere.

Emperor He died early in 106. Real power passed to his widow, Empress Dowager Deng Sui, who governed as regent. She rewarded Cai Lun: in 114 he was made Marquis of Longting with the revenue of 300 households, and later became Grand Coachman of the Changle Palace, the dowager’s household. In 117 she placed him in charge of a project in which scholars at the Eastern Pavilion (Dongguan) library collated and corrected the texts of the Confucian classics and histories.

The Eastern Han court was a dangerous place. Emperors often came to the throne as children, and power was fought over by the families of empresses (the consort clans) and by palace eunuchs. Cai Lun rose through this world and was also stained by it.

Years earlier, under Emperor Zhang, Empress Dou had schemed to remove a rival, Consort Song, whose son was the heir apparent. According to the Book of the Later Han, Cai Lun, acting on Empress Dou’s hints, took part in falsely accusing Consort Song, who then took her own life, and her son was demoted. That son’s son later became Emperor An.

When Empress Dowager Deng died in 121 CE and Emperor An took personal control of the government, he ordered Cai Lun to present himself to the Commandant of Justice. Ashamed to face humiliation, Cai Lun bathed, put on his formal robes and cap, and drank poison. His marquisate was abolished. His tomb is traditionally located at Longting in Yang County, Shaanxi Province, the site of his former fief.

For centuries Cai Lun was simply credited with inventing paper. Twentieth-century archaeology changed that picture. Fragments of paper-like material have been found in tombs and military sites from the Western Han dynasty (206 BCE–9 CE), more than a century before his report.

The most famous find comes from Fangmatan, near Tianshui in Gansu Province, where excavators in 1986 found a fragment of paper with a map drawn on it in a tomb of the early Western Han, around the early second century BCE. It is often described as the oldest surviving piece of paper. Other finds include material from Baqiao near Xi’an (found in 1957) and thousands of fragments from the Han postal station at Xuanquan near Dunhuang, some of them with written characters. Paper with legible writing has been dated to the late first century BCE.

Most of this early paper was made from hemp and was often coarse and uneven. It was used for wrapping, padding and occasionally for writing. Some scholars have questioned whether all these finds are true paper made from pulp, or whether some are felted fibres or mis-dated. The historian of science Pan Jixing was a leading advocate of the view that paper existed well before Cai Lun; others have been more cautious. But the overall conclusion is widely accepted: paper was not invented in a single moment by one person.

In China, paper gradually replaced bamboo slips and silk over the following centuries. By the third century it was a common writing material, and, according to later records, in 404 the warlord Huan Xuan ordered that official documents use paper instead of slips. Paper made possible the growth of written culture: official archives, copies of Buddhist scriptures, calligraphy and painting, and eventually woodblock printing in the Tang dynasty.

Papermaking reached Korea by around the fourth century and Japan by the early seventh; the Japanese chronicle Nihon shoki records that the Goguryeo monk Damjing brought techniques of paper and ink in 610. Along the Silk Roads, paper appears in Central Asia, and by the mid-eighth century it was being made in Samarkand. A famous story says that Chinese prisoners captured at the Battle of Talas in 751 taught the Arabs papermaking, but many historians doubt this, since paper was known in the region earlier.

From Samarkand the craft spread to Baghdad, where a paper mill is recorded around 794–795, then to Syria, Egypt and North Africa. The Islamic world used paper on a vast scale for administration, scholarship and the Qur’an. Paper reached Europe through Muslim Spain, where the town of Xàtiva was a centre of production by the twelfth century, and then Italy, where Fabriano mills in the thirteenth century introduced improvements such as watermarks. Without cheap paper, the European printing revolution of the fifteenth century would hardly have been possible.

Paper was later counted among China’s “Four Great Inventions”, together with printing, the compass and gunpowder, a modern grouping that has become a symbol of Chinese contributions to world technology. Cai Lun is its human face. In imperial China, papermakers honoured him as the patron deity of their craft, offering sacrifices at shrines and temples, and paper guilds bore his name.

Leiyang, his traditional birthplace, and Yang County in Shaanxi, the site of his fief and tomb, both preserve memorials to him. He appears on Chinese stamps and in school textbooks. In the West, he became better known through popular books; Michael H. Hart’s The 100, a ranking of the most influential people in history, placed him seventh.

His story also carries a lesson about how history remembers invention. The name of a single official, recorded because he reported to the emperor, came to stand for the work of countless anonymous craftspeople before and after him. Later papermakers such as Zuo Bo, at the end of the Han, were famous for refining paper further.

Historians of technology also use Cai Lun’s story to show that inventions rarely spread simply because they are better. Paper coexisted with bamboo slips for about three centuries in China, because slips were durable, familiar and cheap in bamboo-growing regions, and old habits of record-keeping were slow to change. Adoption depended on supply, cost, trust in the new material and the decisions of the state.

Historians now distinguish several questions. Did Cai Lun invent paper? No: the archaeological record shows paper-like material in the Western Han. Did he invent paper for writing? Also not strictly, since some Western Han fragments carry writing. What, then, was new? Most scholars point to two things: the introduction of tree bark as a raw material alongside recycled hemp, rags and nets, and the organization of a reliable production process in the imperial workshops that produced paper of consistent quality suitable for official use. The phrase in his biography, “Cai Lun conceived the idea” (倫乃造意), can be read either as original invention or as the design of a new method.

Some scholars also emphasize Cai Lun’s role as a manager rather than a craftsman. As Director of the Imperial Workshops he commanded artisans, and his report may have presented to the throne a process developed collectively. In a bureaucratic culture, credit naturally flowed to the official who submitted the memorial. The later name “Marquis Cai’s paper”, which uses a title he received only in 114, shows how quickly the invention became attached to his person.

A further debate concerns the identification and dating of early finds. Critics of some early claims, such as the Baqiao material, have argued that it may be unprocessed fibre rather than true paper, or that its dating depends on uncertain tomb contexts. Supporters point to fibre analysis showing pulped, randomly oriented fibres, the defining feature of paper. The scholarly consensus accepts that paper existed before 105 CE but remains cautious about specific dates.

Texts. The principal source is the biography in chapter 78 of the Book of the Later Han (Hou Hanshu), compiled by Fan Ye in the fifth century from earlier histories, including the Eastern Han court’s own Records of the Eastern Pavilion (Dongguan Hanji), which survives only in fragments. Because Fan Ye wrote about three centuries after the events, and the biography sits within a chapter on eunuchs, a group Confucian historians generally viewed with suspicion, historians read it both for facts and for moral framing. Some important later chronicles, such as the eleventh-century Comprehensive Mirror (Zizhi tongjian), do not mention his papermaking at all.

Archaeology. Paper fragments from Han tombs, watchtowers and postal stations in the dry northwest, especially Gansu and Inner Mongolia, provide direct physical evidence. Their dating depends on context: associated wooden slips with dates, coins, or tomb furnishings. Documents on dated wooden slips found alongside paper at Xuanquan have been especially important.

Laboratory analysis. Microscopy and fibre analysis identify plant species (hemp, ramie, paper mulberry) and show whether fibres were beaten and dispersed in water, as in true paper, or merely matted. Such studies, pioneered in the twentieth century and continued with modern techniques, allow historians to compare pre-Cai paper with later Han paper and test whether the material changed around his time.

Standard reference works include Tsien Tsuen-hsuin’s volume on paper and printing in Joseph Needham’s Science and Civilisation in China (1985), and, for the westward spread, Jonathan Bloom’s Paper Before Print (2001), which critically examines the Talas story and the role of the Islamic world.