What Else Travelled: Crops, Techniques, Cities

Crops move, and populations follow

• Champa rice came from what is now central Vietnam into Song China. It ripened fast and tolerated drought, so farmers could take two harvests a year on the same land. Chinese population roughly doubled across the Song period, and the surplus fed cities, artisans and an examination-educated elite.
• Bananas travelled the other way, from Southeast Asia across the Indian Ocean into Africa. They grow where grain does not, so they let Bantu-speaking farmers settle wet forest zones that had been thinly populated.
• Sugar moved from South Asia into the Mediterranean with Muslim agriculture, together with citrus and cotton — the plantation package that would later cross the Atlantic.

Techniques and knowledge move with the cargo

The magnetic compass and the sternpost rudder came out of China; the lateen sail and the astrolabe came through the Indian Ocean and the Islamic world. Combined on European ships, they made the voyages of the next unit possible — the technology of 1450 was assembled from borrowings, not invented in one place.

Paper moved from China through the Abbasid world to Europe, and cheap paper is what made large libraries and bureaucracies affordable. In Baghdad and later Córdoba, Greek and Indian mathematics, medicine and astronomy were translated, extended and passed on — including the numeral system Europe would call Arabic.

Cities rise and fall with the routes

Trade cities are infrastructure: Kashgar and Samarkand on the Silk Roads, Hangzhou at the end of the Grand Canal, Calicut and Melaka on the Indian Ocean, Timbuktu at the desert edge, Novgorod in the north. When a route shifted or a state collapsed the city shrank with it — Baghdad never recovered its former position after the Mongol sack of 1258.