Paper is invented in China

Paper is a thin sheet of plant fibres that have been beaten in water until they come apart, caught on a screen, and left to dry into a felted mat. It was invented in China under the Han dynasty. Tradition gives the credit to Cai Lun, a eunuch official at the Eastern Han court in Luoyang, who in 105 CE presented Emperor He with a way of making paper from tree bark, the ends of hemp, old rags and fishing nets. The official history of the dynasty says that from then on paper was used everywhere and was called 'the paper of Marquis Cai'. But archaeologists have found paper in tombs and frontier forts that is two or three centuries older, so 105 is the date of an official report, not of the first sheet.

Before paper, the Chinese wrote on narrow strips of bamboo or wood tied together with cord, or on silk; the history explains that silk was too costly and bamboo too heavy. The oldest papers found so far are coarse, thick sheets of hemp. A scrap with black lines, perhaps a map, lay in a tomb at Fangmatan in Gansu that dates from 179 to 141 BCE; pieces lay under bronze mirrors in a tomb at Baqiao near the old capital Chang'an; others turned up at frontier posts on the northwestern border, at Jinguan on the Juyan line and at the Xuanquan post station near Dunhuang, where hundreds of fragments were found, some with writing. Several of these dates are disputed. Early paper was used for wrapping as much as for writing: in 12 BCE poison for a palace murder came wrapped in a thin red sheet.

Cai Lun's real step seems to have been new raw material. As head of the imperial workshops he used fresh fibre such as the inner bark of the paper mulberry, which could be had in any quantity, alongside second-hand rags and nets. The method he reported is still the method of handmade paper: soak and cook the fibres, pound them to a pulp, dip a screen mould into a vat of pulp and water, lift out a wet sheet, press the pile and dry the sheets on a warm wall. He was made Marquis of Longting in 114. In 121, called to account by the new emperor for his part in an old palace intrigue, he took his own life; he was buried at Longting in Shaanxi, where his tomb and temple still stand, and papermakers in China and Japan worshipped him as their patron saint.

By the fourth century paper had replaced bamboo and wood for books in China, and it travelled with Buddhism, trade and diplomacy. It reached Korea by the third century; Japanese tradition says the Korean monk Damjing brought the craft to Japan in 610. Merchants on the Silk Road wrote letters on paper long before Islam. An Arab writer of the eleventh century said that Chinese prisoners taken at the Battle of Talas in 751 taught papermaking at Samarkand, a story historians now treat as a later tradition, since paper was already known in Central Asia. Under Caliph Harun al-Rashid paper spread to Baghdad, where a paper mill is said to have worked by about 794, and then to Syria and Egypt, where it ended four thousand years of papyrus. Muslim Spain made paper at Xàtiva by the twelfth century, and from about 1276 Fabriano in Italy became Europe's great paper town, adding watermarks by 1282.

Paper changed what could be written down and who could afford it. It carried the Han state's paperwork, Buddhist scriptures and Confucian classics, and later made printing possible: the Diamond Sutra of 868 and the paper money of the Song were printed on it. In Baghdad it fed an explosion of books, from translations of Greek science to The Thousand and One Nights, and in Europe Gutenberg's press could not have worked without paper mills to feed it. Even the word ream, for a bundle of 500 sheets, comes from Arabic. Two thousand years on, paper is still the cheapest way to keep a thought.