The Anji (Zhaozhou) Bridge, designed by the craftsman Li Chun and built under the Sui between about 595 and 605, is the world's oldest standing open-spandrel segmental stone-arch bridge. Its single shallow arch of 28 limestone voussoirs spans some 37 metres, while two open spandrels at each end cut weight and let floodwater pass. The low, flat profile carried roads across rivers without the steep ramps of a tall semicircular arch. The American Society of Civil Engineers named it an International Historic Civil Engineering Landmark in 1991.
The shallow segmental arch let bridges cross wide rivers cheaply and with gentle gradients, a structural idea fundamental to the road and canal crossings that knit Chinese cities together.
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