The Grand Canal (大运河, dàyùnhé) is, at 1800km, the longest canal on earth. The first sections were dug about 400 BC, probably for military purposes, but the historic task of linking the Yellow and the Yangzi rivers was not achieved until the early seventh century AD under the Sui emperor Yang Di, when as many as six million men may have been pressed into service for its construction.
The original function of the canal was specifically to join the fertile rice-producing areas of the Yangzi with the more heavily populated but barren lands of the north, and to alleviate the effects of regular crop failures and famine. Following its completion, however, the canal became a vital element in the expansion of trade under the Tang and Song, benefiting the south as much as the north. Slowly the centre of political power drifted south – by 800 AD the Yangzi basin was taking over from the Yellow River as the chief source of the empire’s finances, a transformation cemented when the Song dynasty established its capital at Hangzhou and the Ming emperors subsequently based themselves in Nanjing. For centuries afterwards, the canal was constantly maintained and the banks regularly built up. A Western traveller, Robert Morrison, journeying in 1816 from Tianjin all the way down to the Yangzi, described the sophisticated and frequent locks and noted that in places the banks were so high and the country around so low that from the boat it was possible to look down on roofs and treetops.
Not until early in the twentieth century did the canal seriously start falling into disuse. Contributing factors included the frequent flooding of the Yellow River, the growth of coastal shipping and the coming of the rail lines. Unused, much of the canal rapidly silted up. But since the 1950s its value has once more been recognized, and renovation undertaken. The stretch south of the Yangzi, running from Zhenjiang through Changzhou, Wuxi and Suzhou, is now navigable year-round, at least by flat-bottomed barges, since passenger services have been killed off by new highways and high-speed trains. North of the Yangzi, the canal is seasonably navigable virtually up to Jiangsu’s northern border with Shandong, and major works are going on to allow bulk carriers access to the coal-producing city of Xuzhou. Beyond here, towards the Yellow River, sadly the canal remains impassable.