Yongtong Bridge, Stone arch bridge in Zhao County, China

Yongtong Bridge is a single-hole open-spandrel stone arch bridge over the Qingshui River outside Zhao County's west gate. It is 32 m long and 6.3 m wide, with a 26 m span and a nearly flat deck. The main arch is built from 21 parallel rings of stone, and four small arches sit on each spandrel.

The construction date is debated: a Jin-dynasty origin in the Mingchang period (1190–1196) was long cited, but stone components and inscriptions excavated beneath the bridge in 1986 point to a start in the early Yongtai years of the Tang (765). The bridge was listed as a Ming-era rebuilding in 1956 and became one of China's first three national protected ancient bridges in 1961.

Locals call it the Small Stone Bridge because it is later and smaller than the nearby Anji Bridge, the Great Stone Bridge. A Zhao County saying sums up the pair: "At the Great Stone Bridge look at the achievement; at the Small Stone Bridge look at the flowers and plants" — a reference to the relief carvings on its parapet panels and on the stones of its small arches.

Visitors can walk across the bridge and examine its stonework up close from various angles. Daytime visits offer the best visibility for viewing the carved details and overall structure.

Yongtong Bridge has the flattest arch profile of any ancient bridge in the world, with a rise-to-span ratio of 0.23: its arch spans 25.9 m but rises only 3 m. A local saying contrasts the two Zhao County bridges: "At the Big Stone Bridge look at the work, at the Small Stone Bridge look at the flowers" — referring to the relief carvings on its parapets and small-arch spandrel stones.