Zhaozhou Bridge (Anji Bridge), Hebei, China

The single flattened stone arch of the Anji Bridge in Zhao County, reflected almost into a full circle in the river below. It was designed by the craftsman Li Chun and built during the Sui dynasty, around 595 to 605. Look at the shoulders of the arch: instead of solid fill, there are two small arches on each side. Those open spandrels lighten the load on the main span of about 37 meters and give floodwater extra room to pass through. It is the oldest open-spandrel stone arch bridge in the world, and its shallow segmental curve keeps the roadway low and easy to climb, a design that has outlasted floods, wars and earthquakes for some fourteen centuries.