Five li south of Zhao County in Hebei Province, there is a large river called the Xiao River. Spanning this river is an open-spandrel, semicircular stone arch bridge with an arch height of seven meters, a width of nine meters, and a clear span of thirty-seven meters—making it the world's earliest surviving and best-preserved ancient stone arch bridge.
About this stone arch bridge, a beautiful legend has been passed down.
Every spring and autumn, heavy rains would fall in Zhao County. The rainwater converged into rivers and, together with mountain springs, formed massive flood peaks. Residents living along both sides of the Xiao River, as well as travelers passing through the area, were greatly inconvenienced by this. The famous master craftsman Lu Ban learned of this situation. So, he traveled from afar and, using his exquisite skills, quickly built a bridge, which became known as the Zhaozhou Bridge. The local people soon heard the news and eagerly came to see it. Everyone praised the bridge for its excellent construction, and more and more people flocked to witness the spectacle. Before long, Zhang Guolao, one of the Eight Immortals, learned of this. Wanting to play a joke on Lu Ban, he called upon Chai Rong, and together they arrived at the Zhaozhou Bridge. Zhang Guolao placed the Sun and the Moon in his bundle and rode on his donkey, while Chai Rong pushed a wheelbarrow loaded with the Five Sacred Mountains. They found Lu Ban and asked if they could cross the bridge together. Confident in his craftsmanship, Lu Ban replied casually, "This stone bridge is extremely sturdy. Even if more people than just the two of you crossed, it would be no problem! If you want to cross, go right ahead!" To Lu Ban's surprise, as soon as Zhang Guolao and Chai Rong stepped onto the bridge, it began to collapse under their weight. Unwilling to see the stone bridge he had built destroyed, Lu Ban immediately jumped under the bridge and supported the eastern side with his hands. In this way, the two immortals, Zhang Guolao and Chai Rong, successfully crossed the bridge with the Sun, Moon, and the Five Sacred Mountains.
In this legend, the Zhaozhou Bridge is said to have been built by Lu Ban, the founding master of craftsmen, perhaps because the bridge was constructed with such extraordinary skill and precision! In reality, the brilliant artisan who built the Zhaozhou Bridge was Li Chun of the Sui Dynasty.
After the Sui Dynasty unified northern and southern China, the society and economy experienced rapid development. At that time, Zhao County served as a key transportation hub connecting the north and south, with routes leading south to Luoyang and north to Zhuozhou, where travelers and horse-drawn carriages flowed continuously. However, the Xiao River outside the city often overflowed during summer and autumn, blocking this vital thoroughfare and causing considerable inconvenience to people's travel. To address this situation, local officials decided to build a stone bridge over the Xiao River. The responsibility for designing and constructing the bridge fell to Li Chun.
After receiving this task, Li Chun led the craftsmen to the banks of the Xiao River, where they surveyed the geological conditions on both sides. Drawing on his years of accumulated practical experience, he selected a relatively straight section of the riverbank as the bridge's location. The strata there had been formed by river alluvium: the surface layer consisted of coarse sand, beneath which were layers of fine gravel, coarse gravel, fine sand, and clay—all fully capable of bearing the pressure exerted by the bridge.
After selecting the optimal location for the bridge, Li Chun faced the issue of sourcing stone materials. Through investigation, he discovered that the bluish-gray sandstone from nearby counties around Zhao County was hard and durable, fully meeting the requirements for bridge construction, so he decided to use local materials. Subsequently, he began designing the bridge, during which he achieved multiple technological innovations.
Before Li Chun, people building longer bridges typically used a multi-arch design. This approach was adopted because the spans between the arches were shorter, the slopes were gentler, and construction was easier. However, multi-arch bridges were not perfect and had their own drawbacks. For example, the piers, after prolonged immersion in water, were prone to erosion and constant water flow impact, which shortened the bridge's lifespan; the many piers also hindered flood discharge and boat navigation. During his design process, Li Chun recognized these shortcomings of multi-arch bridges, so he created a single-arch, long-span design without erecting piers in the river, achieving a stone arch span of thirty-seven meters. This was a groundbreaking feat in the history of Chinese bridge engineering.
Before Li Chun, people built stone bridges using solid-shoulder arches. However, Li Chun changed the solid-shoulder arch to an open-shoulder arch, adding two small arches at each end of the main arch. Compared to the previous solid-shoulder arch, this open-shoulder design had many advantages: first, it saved materials. Second, it reduced the bridge's weight and increased its stability. Third, when floods came, the four small arches could also help discharge water, greatly improving the bridge's flood discharge capacity. Fourth, it made the stone bridge look more beautiful. The four small arches were symmetrically placed on both sides of the main arch, giving the entire bridge a more elegant and light appearance, reflecting artistic beauty. Fifth, it could reduce the pressure on the main arch, greatly enhancing the bridge's load-bearing capacity.
The Zhaozhou Bridge was built in 605 AD, over a thousand years ago. Throughout its long history, it has endured numerous wars, floods, and earthquakes, yet it still stands today over the Xiao River, truly a marvel in the history of Chinese architecture.