Crop circles are patterns created by flattened crops such as wheat or barley. They have been observed since the late 17th century, but became prominent in the late 20th century in England. The phenomenon remains controversial, with debates over whether they are hoaxes or have paranormal explanations. Scientific analysis has found unusual effects on plants inside circles, such as elongated nodes and cell wall changes. While some are intentionally man-made, the origins of many unexplained circles remain uncertain.