Built during the Sui dynasty by the architect Li Chun, the Anji (Zhaozhou) Bridge brings together two innovations in stone-arch engineering — and does so centuries before Europe.

The first innovation is the shape of the arch. Until then, stone arches were generally semicircular; this raises the arch steeply as the span grows, making the crossing steep. Li Chun instead built a segmental arch — one using only an arc of the circle, and so flattened. He crossed the 37-metre span with a rise of only about 7 metres; the bridge is low and graceful, at a gradient carts can climb easily. The price of the flattened arch is a much greater lateral thrust at the supports, which the bridge meets with massive stone abutments.

The second innovation is the open spandrels. Li Chun set two small arches on each side, above the haunches of the main arch. This "open-spandrel" design does three things at once: it reduces the bridge's own weight, saves stone, and lets floodwater pass through rather than push against the bridge. The Anji Bridge has thus stood for 1,400 years and, as the earliest known major example of both the segmental arch and the open-spandrel design, establishes basic principles of bridge architecture in advance.