A crop circle is a sizable pattern created by the flattening of a crop such as wheat, barley, rye, maize, or rapeseed. Crop circles are also referred to as crop formations, because they are not always circular in shape. The documented cases have substantially increased from the 1970s to current times. In 1991 two hoaxers confessed and claimed authorship of circles throughout England. Twenty-six countries reported approximately ten thousand crop circles in the last third of the 20th century. Ninety percent of those were located in southern England. Many of the formations appearing in that area are positioned near ancient monuments, such as Stonehenge. According to one study, nearly half of all circles found in the UK in 2003 were located within a 15km (9.3 miles) radius of Avebury. Archeological remains can cause cropmarks in the fields, in the shapes of circles and squares, but they don't appear overnight and they are always in the same places every year. In 1686, British scientist Robert Plot reported crop circles in his The Natural History of Stafford-Shire, and said they could be caused by airflows from the sky.
Contributions by Darkfred, JiFish, and Stvjns.