Zhaozhou Bridge

The Anji Bridge (simplified Chinese: 安济桥; traditional Chinese: 安濟橋; pinyin: Ānjì Qiáo; literally "Safe crossing bridge") is the world's oldest open-spandrel stone segmental arch bridge. Credited to the design of a craftsman named Li Chun, the bridge was constructed in the years 595-605 during the Sui Dynasty (581–618). Located in the southern part of Hebei Province, it is the oldest standing bridge in China.

Name and location

The bridge is also commonly known as the Zhaozhou Bridge (simplified Chinese: 赵州桥; traditional Chinese: 趙州橋; pinyin: Zhàozhōu Qiáo), after Zhao County, which was formerly known as Zhaozhou (趙州). Another name for the bridge is the Great Stone Bridge (simplified Chinese: 大石桥; traditional Chinese: 大石橋; pinyin: Dàshí Qiáo). It crosses the Xiao River (洨河) in Zhao County, approximately 40 kilometres (25 mi) southeast of the provincial capital Shijiazhuang.


The Anji bridge is about 50 m long with a central span of 37.37 m. It stands 7.3 m tall and has a width of 9 m. The arch covers a circular segment less than half of a semicircle (84°) and with a radius of 27.27 m, has a rise-to-span ratio of approximately 0.197 (7.3 to 37 m). This is considerably smaller than the rise-to-span ratio of 0.5 of a semicircular arch bridge and slightly smaller than the rise-to-span ratio of 0.207 of a quarter circle. The arch length to span ratio is 1.1, less than the arch-to-span ratio of 1.57 of a semicircle arch bridge by 43%, thus the saving in material is about 40%, making the bridge lighter in weight. The elevation of the arch is about 45°, which subjects the abutments of the bridge to downward force and sideways force.

The central arch is made of 28 thin, curved limestone slabs which are joined with iron dovetails. This allows the arch to adjust to shifts in its supports, and prevents the bridge from collapsing even when a segment of the arch breaks. The bridge has two small side arches on either side of the main arch. These side arches serve two important functions: First, they reduce the total weight of the bridge by about 15.3% or approximately 700 tons, which is vital because of the low rise-to-span ratio and the large forces on the abutments it creates. Second, when the bridge is submerged during a flood, they allow water to pass through, thereby reducing the forces on the structure of the bridge.

Li Chun's innovative spandrel-arch construction, while economising in materials, was also of considerable aesthetic merit. An inscription left on the bridge by Tang Dynasty officials seventy years after its construction reads:

Later history and reputation

In the next 1400 years, the bridge survived at least eight wars, ten major floods and numerous earthquakes, the most recent being the 7.2-magnitude Xingtai Earthquake in 1966. Yet, the support structure remains intact and the bridge is still in use. Only the ornamental railings have been replaced every few hundred years.

The Anji bridge influenced the design of later Chinese bridge structures, such as the similar Yongtong Bridge near Zhaoxian 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 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. When Professor Liang Sicheng of Tsinghua University rediscovered the bridge on a field exploration of ancient architecture in Hebei province, made detailed measurements, and published a report and drawing, it became world famous.

Anji bridge was dedicated as an International Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1991. In 1996, the Chinese authorities nominated it for inclusion in the World Heritage List as having "a very important place in the world bridge building history".