In the eighth century the Tang capital, Chang'an, may have been the largest city in the world, with perhaps a million people in and around its walls. Its grid of walled wards held Buddhist temples, Daoist monasteries, a church of the Church of the East, Zoroastrian fire temples and markets where Sogdian, Persian and Turkic merchants traded. The Tang (618 to 907) and Song (960 to 1279) are often seen as high points of imperial China: one for its open, cosmopolitan confidence, the other for its commerce and invention.

The Tang world

The Tang inherited a reunified empire from the short-lived Sui, who had also built the Grand Canal linking the Yellow and Yangzi rivers. Early Tang rulers allotted land to farming households, taxed them evenly, and fielded armies that pushed Chinese power deep into Central Asia. Buddhism flourished, supported by emperors and aristocrats alike.

One ruler stands out. Wu Zetian was the only woman to rule China as emperor in her own name, from 690 to 705, after years of power behind the throne as consort and then empress dowager. Later Confucian historians portrayed her as a ruthless usurper. Modern historians note that she also promoted officials through the examinations and governed competently, and that her critics judged her partly for being a woman.

An Lushan and a census puzzle

In 755 a frontier general named An Lushan rebelled. The war lasted until 763 and wrecked the north. Tang censuses show registered population falling from about 53 million before the rebellion to about 17 million after. That looks like one of history's worst catastrophes, and it is sometimes quoted that way. Yet historians doubt the drop reflects deaths alone, because many people simply fell off the tax registers as the government lost control of whole regions. The war was terrible, but the census mostly measured the state's weakness. The dynasty survived another 150 years as regional governors grew powerful, and it collapsed in 907.

The Song economic revolution

The Song reunified most of China in 960 and presided over remarkable growth. New farming made much of it possible: around 1012 the court distributed Champa rice, a fast-ripening variety from what is now Vietnam that allowed two harvests a year in the warm south. Population passed 100 million. In cities such as Kaifeng and Hangzhou, shops and restaurants lined the streets and stayed open into the night, rather than trading in markets closed behind ward walls.

Commerce outgrew coins. Merchants in Sichuan began using paper deposit certificates, and in the 1020s the government there took over the system, issuing the world's first government paper money, in Sichuan. Later Song and Yuan governments printed money widely, and learned the hard lesson of inflation when they printed too much.

Printing, gunpowder and the compass

Woodblock printing spread under the Tang; the oldest surviving dated printed book is a Buddhist sutra from 868. Under the Song, printing made classics, examination guides and medical texts widely available, and a craftsman named Bi Sheng experimented with movable clay type, a story told in PRNT 101.

Gunpowder came from an unlikely source. Alchemists seeking elixirs of long life mixed saltpeter, sulfur and charcoal and found that the result burned violently. The earliest known written formulas appear in a military manual compiled in 1044. Song armies used fire arrows, bombs and fire lances, tubes that spat flame, which were ancestors of the gun. The magnetic compass, long used for siting houses and tombs, was described in use for navigation at sea by the early twelfth century.

Reform and its critics

Song prosperity sat beside military weakness, and the dynasty paid large sums to northern states such as the Khitan Liao. From 1069 the chief minister Wang Anshi pushed his New Policies to strengthen the state and relieve farmers. The best known, the green sprouts program, offered state loans to farmers at planting time, repaid after harvest with interest lower than moneylenders charged. Opponents led by the historian Sima Guang argued that officials forced loans on people who did not want them and treated the program as a source of revenue. The fight split the bureaucracy for decades.

In the end the north fell. In 1127 the Jurchen Jin dynasty captured Kaifeng and carried the retired emperor and the reigning one north as prisoners, and the Song court fled south to rule from Hangzhou as the Southern Song.

Worked example: a farmer and the green sprouts loan

Picture a farming family in spring, when last year's grain has run out and the new crop is months away. A local moneylender charges very high interest, perhaps doubling the debt by harvest. Under Wang Anshi's plan the county offers a loan at a fixed rate, about 20 percent for the season. On paper the family gains. Now add the details the critics described. The magistrate is judged on how much his county lends and collects, so he presses loans on families who do not need them. Clerks demand fees. If the harvest fails, the state, unlike a neighbor, does not forgive. Both sides in the Song debate were partly right, and the same questions arise whenever a government designs credit for the poor today: who sets the targets, who bears the risk, and how can the people meant to benefit make their complaints heard?