Located to the west of the grand canal from Beijing to Hangzhou, Baodao bridge is 316.8m long. It was built in 816-819 B.C. in Tang dynasty.
Initially at Tang dynasty, the purpose of building Bao dai bridge was to complete the water transportation project-the Grand Canal from Beijing to Hangzhou. During ancient times, staple production mainly relied on south due to the plentiful precipitation and fertile land here. Salaries (grains) for officials, military funds for troops and necessities for civilians were all transported from southern farmlands to northern cities, including the capital city in present day Beijing.
While water transportation was extremely convenient and easy for the most part of the Grand Canal, it met blockage at Suzhou port. During winter, northwest wind blew harshly, hindering the progression of cargo ships. People had to employ ship tractors to struggle providing power for ships. However, with this method, a straight plane for walking is a must. At the conjunction of Dan Tai Lake and the Grand Canal, there appears a large gap, three to four hundred meters in width, cutting the straight route for ship tractors to walk. Building a long arch bridge was the optimal plan and it had a double benefit of discharging flood.
The construction of the complete transporting system gave birth to the prosperity in Suzhou. Commerce grew exponentially, turning Suzhou into the largest economy of Yangtze river delta together with Hangzhou. Businessmen from across the country gathered around Canal banks to organize commercial activities, especially to spread the silk industry all around the world.
Bao dai Bridge is entitled as the longest stone arch bridge in the world. Altogether 53 stone arches comprise the backbone of the whole bridge, which are designed to enhance the intensity of stone materials. At the basis of a stone arch bridge, ancient designers introduced another concept called rigid piers to add strength to the bridge. Part of the piers were deliberately thicker and wider. When flood strikes the bridge, these piers can stand still and hold the bridge up. This concept is now widely employed in modern bridge construction. While some piers are thick, others are thin enough to make the water-discharging area up to 85% of the whole under-bridge area. These creative practices are a perfect embodiment of ancient wisdom of our ancestors.
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