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 recumbent oxen that were secured with other weighty shoreline anchorages by a series of iron chains that replaced bamboo cables. Excavated only in 1989, these iron oxen were approximately 3.3 meters long, 1.5 meters high, and about 15 tons in weight, and were joined as well by life-size iron figures of men.
Each of the eight pairs of small shallow-draft boats is lashed together and connected with a stable pathway to form a pontoon bridge nearly 100 meters long in Pucheng county, Fujian. The intervening space between some of them is traversed merely by a series of parallel timbers that can be moved easily if a boat needs to pass.
Although rarely photographed, pontoon bridges of this type were created utilizing bamboo poles lashed together and then floated on the water. To ease passage on foot, a long mat made of thin slats of woven bamboo was laid across the floating slender bamboo poles.
In some ways, pontoon bridges are reminiscent of what takes shape in a Chinese tale of love regarding the Milky Way, which Chinese traditionally saw as a luminous “silver stream” in the heavens. On the seventh day of the seventh month each year, Niu Lang and Zhi Nu, a cowherd and a weaving girl, were allowed to meet when all the magpies on earth flew to heaven and formed a bridge over the galactic stream for them to cross and meet.
In this photograph taken in the 1930s somewhere in southern China, there is only one gap in the adjacent boats that can be opened for river traffic to pass through.
Cantilevered Beam Bridges
Simple wooden and stone beams have limits to the distances they can span, rarely reaching 10 meters. Each quarried stone or cut timber, the most common materials traditionally employed in cantilevered bridges, has an unspecified strength depending on the species and type. Even when they appear homogeneous, each usually contains invisible pockets of weakness. Downward pressures brought on by an increased live load can lead