The towpath thus served as a passageway for trackers who were needed to pull the heavily laden boats along. While the canal boats were usually propelled by sails or by sculling, sometimes it was necessary to tow them when strong seasonal winds made sailing difficult.
The gradual incline of a set of steps makes it possible for two adjacent canals to be connected.
As this model clearly reveals, the Bazi Bridge is actually a combination of two bridges juxtaposed so that it connects multiple lanes while facilitating canal traffic.
Some portions of the towpath were built immediately adjacent to land; indeed, at some locations trackers actually moved on land before reaching another stone pathway, but in others the towpath was very much like a bridge as stone beams supported by stone piers rose a meter or so above the water. In terms of materials used and techniques of construction, tow-paths differed little from common stone beam bridges that crossed streams. Each of the piers supporting the towpath is composed of a stack of granite blocks approximately 1.5 meters thick. Each span between them is made up of three or more rough-cut stone beams that exceed 2 meters in length and have a width of 3 meters. At intervals along the towpath, a section is elevated to permit the passage of small boats plying the intricate canal network of this region.
An outstanding and complex stone beam bridge with many components is the Bazi (Character Eight) Bridge in the southeastern section of Shaoxing, Zhejiang, a city that had in 1903 some 229 fine bridges along its 29 canals. The oldest extant urban bridge in China, the Bazi was constructed in 1256 during the later Song dynasty. Located to meet the needs of foot and water traffic at the junction of three canals and three lanes, the structure is actually made up of two juxtaposed bridges that are reminiscent of the Chinese character ba representing the number eight. The principal span clears 4.5 meters, rises some 5 meters, and has a width of 3.2 meters. Four-meter-long stone columns are slightly cambered to support the main span. The columns are themselves supported by a double layer of quarried stone 1.8 meters thick atop a foundation of stone boulders, which together constitute the support for the abutments. Including the balustrades and approach steps, the bridge is assembled from countless quarried slabs forming a structure of incalculable weight and substantial versatility that fits compactly into a tight residential environment. Overall the stepped approaches are gentle and have been modified to facilitate the movement of carts and bicycles.
With the tide in, the mudflats beneath the Luoyang Bridge in Quanzhou are submerged. The prow-like triangular cut-waters point upstream.
This is a remnant of a long nineteenth-century stone beam towpath along the Xiaoshan-Shaoxing Canal that extended water transport beyond the Hangzhou terminus of the Grand Canal. When there was little wind to fill the sails of boats, trackers on the towpaths used ropes to pull the heavily laden boats.
Handling large timbers and heavy stone columns set limits to what bridge builders could accomplish with available materials. In the middle two centuries of the Song dynasty (960–1279), extraordinary megalithic stone bridges built with granite piers and granite beams began to be built along the embayed shoreline of Fujian in southeastern China. The broad tidal inlets at the mouths of short turbulent rivers provided substantial challenges to spanning them with structures of any type, let alone utilizing megaliths. The methods employed in building massive stone bridges in Fujian remain a relative mystery, but there is no doubt that more than ordinary skills were required to maneuver stone slabs that reached 20 meters in length and 200 metric tons in weight. It is an amazing feat that stone beam bridges totaling 15 kilometers in length were constructed in a relatively brief thirty-year period alone throughout Fujian to help integrate an expanding transportation network. While there may once have been a bridge nearly three times longer, the Anping (Peace) Bridge, built between 1138 and 1151, is today heralded as “no bridge under the sun is as long as this one.” The bridge, which today is 2070 meters long, 10 percent shorter than it once was, was constructed using 6–7 granite slabs, each of which is 8–10 meters long, laid atop 331 stone piers. Another remarkable megalithic bridge still standing is the Luoyang Bridge, begun about 1053 and completed in six years. Today, only some 800 meters of the bridge’s original 1100-meter length and 31 of 47 piers remain. Some of the 11-meter-long granite slabs forming the deck weigh as much as 150 metric tons and were positioned using the ebb and flow of the tides. Bridge builders utilized an ingenious method of securing components of the stone foundations by employing living oysters as an organic mastic within crevices in the stone in order to strengthen the structure.
Built between 1138 and 1151 during the Song dynasty, the megalithic Anping (Peace) Bridge is even today more than 2 kilometers long. Over 330 piers of stacked carved granite lift heavy stone slabs of varying dimensions, some of which were infilled over time with smaller sections of stone because of the shifting that occurred in the structure.
Floating Bridges
King Wen, who laid the foundation for the Zhou dynasty some 3,000 years ago, is said to have made one of the earliest technological improvements over simple wooden beam bridges by lashing together boats to form a floating or pontoon bridge across the Wei He River. Employing side-by-side boats that then held up wooden planks, essentially beams laid transversely across the boats, floating bridges of this type became quite common in China as a means to span wide and deep, even swiftly moving streams. In general, pontoon bridges cope well with fluctuations in water level, variations in stream velocity, and the common need to accommodate navigation by other boats. At relatively low cost, pontoon bridges provided a relatively quick solution to a need in facilitating land transport. While small boats provide the support for most floating bridges, in China bamboo rafts, barrels, animal skins, wagon wheels, even calabashes have been used to support logs and planks. Pontoon bridges are usually formed a section at a time until the opposite bank is reached. In addition to cables and chains linking the boats together, “stones turtles”—woven containers of stone rubble—were sometimes dropped to the stream’s floor as anchors to moor groups of boats. Floating bridges demanded careful monitoring in response to river flow and traffic so that cables and anchorages could be adjusted to keep approaches relatively level.
In many parts of the world, floating bridges are viewed only as temporary structures, but in China many have endured for centuries. In one fashion or another, floating bridges made of linked wooden boats have stretched across the Gan River in Ganzhou, Jiangxi, since the Song dynasty. However, today only the Dongjin Bridge, with a length of 400 meters across 100 small wooden boats, remains. While most floating bridges provided only a mere walkway for pedestrians or simple wheeled carts, others in the twentieth century were capable of bearing vehicular traffic such as cars, trucks, and buses across two lanes. During warfare especially, pontoons were capable of being assembled quickly, serving a purpose, and then removed before they could be used by one’s enemies.
China’s most important rivers, the Huang He or Yellow River and the Chang Jiang or Yangzi River, both have several millennia-long histories of being spanned by precursor pontoon bridges, even as constructed bridges did not span them until the middle of the twentieth century. The Huang He saw its first floating bridge in 541 BCE and the Chang Jiang in CE 35, with dozens more built in the centuries following that utilized improvements in anchorages and connections. In Yongji county in southern Shanxi, the restoration of the Puji Floating Bridge during the Tang dynasty in 724 brought with it an especially noteworthy innovation—the use of heavy cast iron anchorages in the shape of large
