What is the world's largest natural arch?

The world's largest known natural arch is Xianren Bridge, also called Fairy Bridge, in Guangxi, China. The limestone arch spans the Buliu River in a remote karst landscape shaped by water erosion.

The Natural Arch and Bridge Society measured its span at about 400 feet (121.9 meters) in 2010, placing it well ahead of other famous natural arches. The formation is a natural bridge because a river helped carve the opening beneath the remaining limestone roof.

Xianren Bridge remained little known internationally because it is difficult to reach. The surrounding area is remote, and visitors traditionally needed a lengthy rafting journey on the Buliu River before reaching the formation. It was reportedly identified by outside explorers only in the early 21st century, with its major measurement expedition taking place in October 2010.

A common mix-up is Landscape Arch in Utah, which is famous for its remarkable length and thin rock span. Landscape Arch measures about 290 feet, however, so it ranks below Xianren Bridge. Delicate Arch and Australia's London Arch are also iconic formations, but neither has the world's longest recorded natural-arch span.