The Silk Road: Trade, Paper, Baghdad and the Mongols

Zhang Qian goes west

A globe turns, and a line of camels sets off from Chang’an, today’s Xi’an, towards the setting sun. Between about 138 and 126 BC the envoy Zhang Qian travelled west for the Han emperor Wu to look for allies against the Xiongnu. He was captured, lived for years among nomads, and came home with news of Central Asian kingdoms and the famous Ferghana horses. Trade routes soon grew. The name Silk Road was coined only in 1877 by the German geographer Ferdinand von Richthofen. It was a web of paths, some 6,400 kilometres from Chang’an to the Mediterranean, and almost nobody travelled all of it.

What the caravans carried

Packs are unloaded and glow with colour: bolts of silk, sacks of spice, glass bowls, bundles of paper and strong horses on ropes. Goods changed hands again and again in oasis towns, so each merchant covered only a short stretch. But the routes carried more than goods. Buddhism travelled from India into China, and Islam, Christianity and Manichaeism moved along the same roads, together with number systems, songs and recipes. Historians think diseases travelled too. We know this from coins, textiles and manuscripts found in desert towns such as Dunhuang, where a sealed cave held tens of thousands of documents.

A house for knowledge

The picture moves to a round city on the Tigris. Baghdad was founded in 762, and in the 9th century the Abbasid caliphs supported scholars in the House of Wisdom, who worked to translate Greek, Persian and Indian books into Arabic. Historians still debate exactly how it was organised, whether as a library, an academy or both. One scholar, Muhammad al-Khwarizmi, wrote a book around 820 on solving equations by balancing them. Its word al-jabr gave us the word algebra, and his own name gave us the word algorithm. Knowledge from many lands met on those shelves and was later handed on to Europe.

How we see

Light now streams through a single small hole into a dark room and draws an upside-down picture on the wall. Ibn al-Haytham, who worked in Cairo, wrote his Book of Optics between about 1011 and 1021. He argued, against older ideas, that we see because light enters the eye rather than leaving it, and he tested claims with experiments. Many historians call him an early pioneer of the experimental method, though others point out that earlier scholars also tested ideas. His book was translated into Latin and read by European scientists centuries later. It shows that the roads of trade were also roads of ideas.

Paper goes west

A sheet of paper is lifted from a vat and dries in the sun. By tradition the court official Cai Lun presented paper to the Chinese emperor in AD 105, although archaeologists have found older paper fragments in China. Paper reached Samarkand by the 8th century, and Baghdad had a paper mill around 793. A popular story says the secret spread after the Battle of Talas in 751, when Chinese prisoners taught their Arab captors. Historians treat that tale as a tradition with little firm proof. What is certain is that paper was cheaper than parchment, so books, letters and records multiplied, and it reached Spain and Christian Europe by the 12th century.

The Mongol bridge

Riders gallop across the whole map, and the borders melt into one colour. Genghis Khan united the Mongol tribes in 1206, and his successors built the largest contiguous land empire in history, about 24 million square kilometres at its height. The conquests killed enormous numbers of people and destroyed cities, and that cannot be set aside. Yet once the lands were under one rule, travel and trade grew safer, a time sometimes called the Pax Mongolica. Around 1271 the Venetian Marco Polo set off for Asia and returned in 1295. His book describes China, though some scholars doubt he saw everything he wrote about, and the question is still debated.

The Silk Road