Zhaozhou Bridge combines a large stone arch with smaller arches in its shoulders. These openings reduce the bridge's weight and provide additional room for water when levels rise.
Built during the Sui dynasty in Zhao County, Hebei, the bridge's stone connections and distribution of forces make it an important example of ancient Chinese bridge technology.
History
Starting from 581 CE, the Sui dynasty reasserted imperial control over the competing powers that had ruled various regions of China since the decline of the Han dynasty in the third century. Thus immense public works projects were carried out, including the rebuilding of two grand imperial capitals, the excavation of the 2400-kilometer-long Grand Canal, and major improvements to the fortifications that predated the Great Wall. Economically, the long-distance transport of goods and men was a critical component to the interests and sustainability of the ruling house. The movement of goods by land south and southwest from the North China Plain to the Central Plains around Kaifeng and Luoyang followed a path that crossed the Xiao River near Luanzhou (later Zhaozhou and now Zhao County) in today's Hebei province.
Flowing west to east through a plain that was relatively low-lying on both sides, the Xiao River was an important artery for transporting goods, but an impediment to continuous overland movement and the economic integration of China's regions.
It was under these circumstances that Li Chun, who directed masons and other craftsmen, built the Anji (Safe Passage) Bridge, also called Dashi (Great Stone) Bridge. Although Chinese history credits Li Chun with the design and building of the Anji Bridge, no contemporaneous materials recorded the process, however later chronicles do make notes of it in brief.
The Anji Bridge is among the most remarkable achievements of Chinese bridge building for exhibiting a segmental arch design of wholly stone construction. This innovation, which occurred between the end of the sixth century and beginning of the seventh century, repudiated conventional wisdom that a semicircular arch was necessary to transfer the weight of a bridge downwards to where the arch tangentially meets the pier. The double pair of openings piercing both ends of the arch spandrel, which as well as accentuating its lithe curvature, lightens the weight of the bridge and facilitates the diversion of flood waters by allowing them to pass through the auxiliary arches rather than pound against the spandrels. The Zhaozhou Bridge is celebrated as China's oldest standing bridge and the oldest open spandrel stone bridge in the world.
The Anji Bridge influenced the design of later Chinese bridge structures, such as the similar Yongtong Bridge near Zhao County in Hebei. The Yongtong Bridge is a 26 m (85 ft) long stone segmental-arch bridge built in 1130 by the Song structural engineer Pou Qianer.
The intriguing design of the Anji Bridge has given rise to many legends. According to one legend, the bridge was built by a master architect of the mid-1st millennium BC named Lu Ban in a single night. In another story the bridge was put to the test by two immortals who crossed it at the same time, and Lu Ban saved it by wading into the water and supporting the structure.
Although Ming dynasty (1368–1644) authors compared the bridge to "a new moon rising above the clouds" and "a long rainbow hanging on a mountain waterfall", it later fell into obscurity. In the 1930s, professor Liang Sicheng of Tsinghua University rediscovered the bridge on a field exploration of ancient architecture in Hebei province. He made detailed measurements and published a report and drawing, restoring its reputation and giving it new recognition. By the time Liang visited the bridge, all of the original stone carving surfaces were gone. In a few cases, they were given replacements dating to the Ming dynasty.