Chinese Empire

The Construction of the Grand Canal: The Sui Emperor’s Project That Changed China

The Grand Canal (大運河, Dàyùnhé) of China is the longest artificial waterway in the world and the largest civil engineering project undertaken before the modern era. It runs from Beijing in the north to Hangzhou in the south, a north-south distance of about 1,770 kilometres, and links five major river systems: the Hai River, the Yellow River, the Huai River, the Yangzi River, and the Qiantang River. The Grand Canal in its present form was assembled over more than a thousand years, but its crucial first stage was the Sui-dynasty project, ordered by the Sui Emperor Yang (r. 604–618) in the early seventh century, that linked the Huai and Yellow river basins for the first time. The wider context of Chinese engineering is surveyed in our overview, and the canal is treated as part of the engineering marvels of imperial China. The irrigation system at Dujiangyan, the other great Chinese water engineering project, is treated in our article on Dujiangyan.

The Background: Local Canals in the Pre-Sui Period

The Grand Canal grew out of a long tradition of canal building in the lower Yangzi and Huai regions, beginning in the Spring and Autumn period (770–476 BCE) and the Warring States period (475–221 BCE). The earliest known Chinese canal is the Hangou Canal (邗溝) in Jiangsu, dug in 486 BCE by the state of Wu. The state of Wei, in modern Henan, dug the Honggou Canal (鴻溝) in 361 BCE, connecting the Yellow River with the Huai via a tributary system. Other states also dug local canals for irrigation and transport.

These local canals were extended and connected in the Qin and Han periods, but they were never unified into a single north-south system. The situation changed in the Six Dynasties period (220–589 CE), when the political centre of China shifted south to the Yangzi valley and the southern rice bowl grew in economic importance. The Eastern Jin and the Southern Dynasties, ruling from Jiankang (modern Nanjing), relied on the south for grain and tax revenue, and the canal system of the Huai and lower Yangzi regions was developed rapidly. By the sixth century, the Northern Qi and Northern Zhou dynasties of the north had begun to extend these waterways northward across the Yellow River.

The Sui Emperor Yang’s Project

The Sui dynasty (581–618 CE) reunited China in 589 by conquering the Chen in the south. The Sui capital was at Daxingcheng (later Chang’an, see our article on Tang Chang’an) in the northwest, but the new dynasty needed to move grain and tax revenue from the productive south to the political centre, and this required a long, continuous waterway.

The project was begun in 605 CE by the Sui Emperor Yang (Yang Guang, r. 604–618), the son of the dynasty’s founder, who was determined to complete the canal as a show of imperial power. The first stage, completed in 610 CE, connected the Huai River with the Yangzi River at Yangzhou, and the Yangzi with the Qiantang River at Hangzhou, in the south; and connected the Huai with the Yellow River at Shanyang (modern Huai’an in Jiangsu), in the north. The second stage extended the canal further north to Luoyang, the eastern Sui capital, via summit-level canals in Henan.

The work was carried out by conscripted labour on a vast scale. The official histories record that the Sui mobilised more than a million men for the southern section, and similar numbers for the northern section. The labourers were conscripted from the peasantry, often for years at a time, and mortality is believed to have been enormous. The Sui also used soldiers and prisoners of war, and the work was a major contributor to the social unrest that would eventually topple the dynasty in 618.

The engineering challenges were formidable. The route had to cross several natural watersheds, requiring summit-level canals supplied by elaborate feeder channels. The Yellow River carried enormous loads of silt and was perched above the surrounding plain in its lower course; the canal had to be routed so that it could draw water from the river without being clogged by silt, and the river itself had to be stabilised by levees. The Sui solution was to build a long, low canal that used the natural slope of the terrain to maintain a flow, regulated by a series of flash locks — temporary dams opened to allow a boat to pass, and closed again. Flash locks were simple and cheap but slow. They were eventually replaced, in the Song dynasty, by the more sophisticated pound lock — a pair of lock gates enclosing a chamber, which raised or lowered boats between two water levels without loss of water. The pound lock was transmitted to Europe in the late Middle Ages, where it became the basis of the European canal-building tradition.

The Tang, Song, and Yuan Periods

The Sui fell in 618 CE, and the Tang dynasty (618–907) inherited the canal system. The Tang made the canal one of the principal grain arteries of the empire and rebuilt the locks and feeder channels. The An Lushan Rebellion of 755–763 temporarily disrupted the canal, and the late Tang emperors increasingly relied on Luoyang rather than Chang’an for the political centre.

The Song dynasty (960–1279) inherited the Sui-Tang canal system and developed it further. The Northern Song capital at Bianjing (modern Kaifeng) was located directly on the canal, and the canal became the principal means of supplying the city with grain from the south. The Song developed the pound lock to a sophisticated form. The Southern Song lost the northern part of the canal to the Jurchen Jin dynasty in 1127, and the canal fell out of use as a north-south artery.

The Yuan dynasty (1271–1368) reunified China under Mongol rule and inherited both the former Jin capital in the north and the Southern Song capital at Hangzhou in the south. The new Yuan capital was at Dadu (大都, “Great Capital”), on the site of modern Beijing. To connect the southern grain bowl with the new capital, the Mongols undertook the final major extension of the Grand Canal. The Yuan project, completed in 1292 under the emperor Kublai Khan and his successor Temür Khan, extended the canal from the old Tang endpoint at Hangzhou in the south to Dadu in the north. The work was carried out under the supervision of the Mongol engineer Guo Shoujing. The result was the Beijing-Hangzhou Grand Canal (京杭大運河), the system that survives today. Canal-side towns of Jining, Linyi, Cangzhou, and Tianjin grew up along its route.

The Ming and Qing Grand Canal

The Ming dynasty (1368–1644) inherited the Yuan canal and made it the principal grain artery of the empire. The Yongle Emperor moved the Ming capital to Beijing in 1421, and the Grand Canal became the principal means by which the southern grain was moved to the northern capital. The Ming rebuilt the Southern Canal (南運河) in the lower Yangzi region and opened new sections through the Shandong hills. The caoyun (漕運, “canal transport”) system of grain shipments carried about 4 million shi (about 250,000 tons) of grain per year from the south to the north at the peak of the Ming system in the sixteenth century. The Forbidden City in Beijing was the principal destination of these shipments.

The Qing dynasty (1644–1912) inherited the Ming system and made few changes to the basic route. The canal remained a major grain artery throughout the Qing period, and the canal-side towns of Hangzhou, Suzhou, Yangzhou, Huai’an, and Tianjin were among the most prosperous in the empire. The canal began to decline in the late nineteenth century, as railways and coastal shipping offered faster alternatives. The last imperial grain shipment travelled the canal in 1901. The Grand Canal of China was inscribed as a UNESCO World Heritage Site in 2014.