The original Grand Canal (Da Yunhe), like the Great Wall, was not one but a series of interlocking projects from different eras. The earliest parts were dug in 486 BC in the north to facilitate troop movements, and the entire route opened to navigation in 1293 AD, last for 1779 years. During the Sui Dynasty (582 - 618 AD), the ruthless Emperor Yang Di conscripted a massive workforce to link his new capital of Luoyang to the older capital of Changan (today's Xi'an). Then he extended the project down to Hangzhou in less than a decade, making it possible for junks to go along the Yangtze, up the Canal, and on to ports along the Yellow River - a trip that might take up to a year.
The Grand Canal starts Beijing, flows through Hebei, Shandong, Jiangsu and ends in Hangzhou, Zhejiang, totally 1794 kilometers in length. It links up four major rivers: - the Huang (Yellow), Yangtze, Huai and Qiantang, which all run east-west. It thus gives China a major north-south transport route, and links the compass points. This feat, the construction of the longest man-made waterway in the world, was accomplished by a million men with spades, some estimate closer to five million. By even the crudest mathematics, the cost in lives must have been enormous. 
The emperor was not so much interested in unification as subjugation; grain from the rich fields of the south was appropriated to feed the hungry armies in the northern capitals. In the Tang Dynasty 100,000 tons of grains were transported annually to the north; long chains of imperial barges loaded with tax grain plied the waterways.
In the 13th century, Kublai Khan used the work of his predecessors for much the same purpose and he did a bit of remodeling to bring the northern terminus up to Beijing, his capital. Marco Polo noted what boats were pulled along by horses, which walked along the banks of the canal pulling the boats with long harnesses and in this way large quantities of corn and rice were shipped northwards.
'This magnificent work (the canal) is deserving of admiration; and not so much from the manner in which it is conducted through the country, or its vast extent, as from its utility and the benefit it produces to the cities which lie in its course'. Apart from bringing prosperity to the towns along its course, the canal was also a means by which the sybaritic emperors would move from point A to point B; at one point, in Emperor Qianglong's reign, it was suggested that the grain fleets be removed from the canal so as to allow the imperial pleasure-cruisers a freer passage.
The section which flows through Suzhou is about 81.8 km. Its proper cuts to the west and south of Suzhou, within a 10 km range of the old city. Most tourists from home and abroad like to cruise on the canal to enjoy the night scene of Suzhou.