Zhaozhou Bridge: The World's Oldest Open-Spandrel Stone Arch

The Zhaozhou Bridge, also called the Anji Bridge, is a stone arch bridge over the Xiao River in Zhao County, Hebei Province, northern China. Built around 595–605 during the Sui dynasty and credited to the craftsman Li Chun, it is the oldest standing open-spandrel segmental arch bridge in the world. Its shallow, light design was centuries ahead of its time and has allowed it to survive floods, earthquakes and wars for more than 1,400 years.

Background

The Sui dynasty reunified China in 589 and invested heavily in infrastructure, from the new capital Daxing to the Grand Canal. Zhaozhou lay on an important road running north and south across the North China Plain, and the Xiao River, which could flood violently in the rainy season, was an obstacle to travellers and officials.

The exact date of construction is not recorded in surviving official histories. It is usually placed in the Kaihuang and Daye reign periods, roughly 595 to 605, on the basis of inscriptions and later local records.

Design and engineering

Most early stone arch bridges, in China and in the Roman world, used semicircular arches. These are strong but tall, which means steep approaches and many piers for long spans. Li Chun instead used a single segmental arch, a flattened section of a circle, with a clear span of about 37 m and a rise of only about 7 m. The ratio of span to rise is roughly 5 to 1, so the roadway is low and easy to climb.

Above the main arch, at each end, he placed two small open arches in the spandrels. These had several benefits:

• They reduced the weight of the bridge, and so the load on the foundations.
• They saved stone.
• In floods, water could pass through the side arches, lowering the pressure on the structure.

The main arch is not one vault but 28 parallel arch rings set side by side and tied together with iron bars and stone keys. This allowed damaged rings to be repaired individually. The bridge is about 64 m long and about 9 m wide, and its foundations rest directly on compacted natural soil with relatively shallow footings.

Key people

• Li Chun: the builder named in a Tang-dynasty inscription by the official Zhang Jiazhen, which praised his skill. Nothing more is known about him.
• Liang Sicheng (1901–1972): the pioneering architectural historian whose team surveyed the bridge in 1933 and made it widely known to scholars inside and outside China.

Survival and restoration

The bridge has outlived many hazards. According to local records it survived numerous floods, at least eight wars and many earthquakes, including the strong Xingtai earthquakes of 1966, centred not far away in southern Hebei. Some of the outer arch rings on the western side collapsed in the Ming dynasty and were repaired, and further rings fell in the Qing period.

A major restoration between 1955 and 1958 rebuilt damaged rings and replaced many facing stones and balustrade panels. Some original carved panels, decorated with dragons and other animals, were recovered from the riverbed and are now displayed nearby. Critics note that the restoration altered parts of the original fabric, but the overall form remains authentic.

Myths and facts

A well-known folk tale says the bridge was built in a single night by Lu Ban, the legendary patron of Chinese carpenters and masons. In the story, immortals riding over it to test its strength left marks of hooves and cart wheels, which local people still point out on the stones. These are legends; historical sources credit the bridge to Li Chun.

The bridge is also sometimes described simply as the oldest stone bridge in the world. That is not correct: Roman stone arch bridges such as the Pons Fabricius in Rome (62 BC) are centuries older. Its record is more specific, as the oldest surviving bridge of the open-spandrel segmental arch type.

Legacy

The Zhaozhou Bridge inspired other Chinese bridges, such as the smaller Yongtong Bridge nearby in Zhao County, and it became a symbol of Chinese engineering skill. In 1961 it was listed among China’s first group of major historical and cultural sites protected at the national level. In the wider history of bridge building it predates by centuries European landmarks such as Prague’s Charles Bridge, begun in 1357, and the first cast-iron bridge at Coalbrookdale, completed in 1779.

Timeline

• 589: The Sui dynasty reunifies China.
• c. 595–605: Li Chun builds the bridge over the Xiao River at Zhaozhou.
• Tang dynasty: Zhang Jiazhen writes an inscription praising Li Chun’s work.
• Ming and Qing dynasties: Several outer arch rings collapse and are repaired.
• 1933: Liang Sicheng’s team surveys and photographs the bridge.
• 1955–1958: A major restoration rebuilds damaged sections.
• 1961: The bridge is listed as a nationally protected monument.
• 1966: It survives the Xingtai earthquakes.

Why it matters

The Zhaozhou Bridge shows that Sui-dynasty builders had mastered a light, efficient arch design many centuries before it became widespread elsewhere. Still standing after fourteen centuries, it is one of the world’s great surviving works of early engineering.