7. Weiqiao bridge relics from the Western Han Dynasty (206 BC-AD 24) to the Eastern Han Dynasty (AD 25-220), Xi'an, Shaanxi province

Evidence of seven bridges was found on what was once the course of the Weihe River. Strangely, five of them are located within a short distance of 400 meters. The longest one was 880 meters long, and believed to be the world's longest bridge built with wooden beams and columns. These were also the first bridges from Chang'an (today's Xi'an) westward via the Silk Road.

Numerous vestiges of repair were observed, ranging for several successive dynasties. Discovery of 17th-century coins in the riverbed proves the Weihe River did not change its current course earlier than that period of time.

"The discovery fills the academic void on ancient bridges of Chang'an, the capital of so many dynasties in China," says Liu Rui, a deputy researcher with the Institute of Archaeology under the Chinese Academy of Social Sciences. "It was where many historic incidents occurred, and the discovery will also help us better understand how the local natural environment changed in ancient times."