Before there could be a book market, there had to be something cheap to write on. Papyrus came mainly from Egypt, and parchment, made from animal skins, was costly: a single large book could need the skins of a whole flock. Paper changed the economics of writing, and the Islamic world was the first region outside East Asia where it became an everyday material.

The coming of paper

Paper was invented in China, and by the eighth century it was being made in Central Asia. A popular story says that Chinese prisoners captured at the Battle of Talas in 751 taught papermaking to Muslims in Samarkand. Historians now doubt the Talas story, since paper was already known in Central Asia before the battle. By the 790s paper was being made in Baghdad, and over the following centuries papermaking spread to Syria, Egypt, North Africa and Spain. Abbasid officials came to prefer paper for government records, partly because, according to medieval writers, writing on paper was hard to erase without leaving a trace, making forgery harder than on parchment, which could be scraped clean.

Cheap paper fed a book culture. Baghdad had a market of warraqin, stationers and booksellers who copied books to order, sold them and kept shops where scholars met to talk. The bookseller Ibn al-Nadim finished his Fihrist, a catalogue listing thousands of titles on every subject, in 987. Paper reached Christian Europe through Muslim Spain and Sicily; Xàtiva, near Valencia, had a paper industry by the twelfth century.

Trade across three continents

The Abbasid world sat across the routes linking the Mediterranean, the Indian Ocean and Central Asia. Ships sailed from Basra and Siraf on the Persian Gulf to India and China, timing their voyages to the monsoon winds, which blow one way in summer and the other in winter. The hajj, the pilgrimage to Mecca, brought people together from across the Muslim world every year, spreading goods, news and ideas. Merchants built tools for moving money without carrying coins. The sakk was a written order to pay, and the suftaja, a kind of bill of exchange, let a merchant deposit money in one city and collect it in another.

A rich window onto this world is the Cairo Geniza, a storeroom in a synagogue in Fustat, old Cairo, where for centuries Jews placed worn papers that might bear the name of God and so could not be thrown away. The Geniza preserved hundreds of thousands of fragments, including merchants' letters, contracts and accounts, many from the eleventh and twelfth centuries, showing Jewish traders working with Muslim partners from Spain to India.

The other side of the ledger

Trade also moved people against their will. Slavery was widespread, as it was across the medieval world. Enslaved people were brought from Africa, Central Asia and Eastern Europe; some served in households, some as soldiers, and some labored in brutal conditions. In southern Iraq, enslaved East Africans known as the Zanj were forced to strip salt crusts from marshland to make it farmable. The Zanj rebellion of 869 to 883 was one of the largest slave revolts in history, holding territory for more than a decade before Abbasid armies crushed it. Islamic law praised freeing slaves as a pious act and set rules for their treatment, but it did not abolish slavery, and no society of the time did. A history that admires Baghdad's libraries should not forget whose labor built its prosperity.

Cities and institutions

Cities grew around a mosque, a market and a governor's palace. The waqf, the charitable endowment met in the hospital level, also paid for fountains, schools and inns for travelers. From the eleventh century, colleges called madrasas spread, teaching law and the religious sciences; the vizier Nizam al-Mulk founded a famous network of them, the Nizamiyyas, beginning in Baghdad in 1067. English words such as tariff, magazine, sugar and cotton came through Arabic, a sign of how much Europe later absorbed from these markets.

The historian Andrew Watson argued that an agricultural revolution spread new crops west, such as rice, sugar cane, cotton and citrus fruits, along with new irrigation methods. Others think Watson overstated how new and how widespread these changes were. The debate is a good example of a large, attractive claim being tested crop by crop and region by region.

Worked example: a merchant's letter

Picture a letter of the kind found in the Geniza, written around 1100 by a Jewish merchant in Aden to his partner in Fustat. He reports that pepper prices in India are high, that a ship has been lost with part of their cargo, that he has sent a bill of exchange instead of cash for safety, and that he hopes the partner's son is recovering from illness. What can a historian learn? That trade relied on trust between partners separated by months of travel; that credit instruments reduced risk; that losses were common; and that business and family life were tangled together. Letters like this, often written in Arabic using Hebrew letters, also show ordinary people, not just famous scholars, sharing one written culture across lines of religion.