Xianren Bridge is a natural arch created by flowing water that has the world's longest recorded span.[1] Carved of limestone karst, the formation bridges Buliu River in the northern Guangxi Zhuang Autonomous Region, China. Because of its remote location, accessible only by a three-hour rafting trip, it was not discovered until 2009[2] and remains relatively obscure. An expedition in October 2010 by the Natural Arch and Bridge Society first measured the bridge's span and found it to be 121.9m±4.6mm (399.9feet±15.1feetm) in length.[3] [4]