A moon bridge is a highly-rounded arched pedestrian bridge associated with gardens especially in China and Japan, where the design originated. In many areas, moon bridges are purely decorative, but at one time this type of bridge was originally designed to allow pedestrians to cross canals while allowing the passage of barges beneath. When constructed using the climbing ascent and descent, it has the further advantage of not using space from the adjoining fields for approaches to the bridge. The visual effect of this bridge makes it a popular design for gardens, particularly those with water or small paths.
info source: wikipedia
Moon bridge in The Japanese garden at Huntington Gardens in San Marino, California.- By https://www.flickr.com/photos/randysonofrobert/ – https://www.flickr.com/photos/randysonofrobert/464791157/, CC BY 2.0, Link