Photograph by Sandra Campardo, AP Photo/Keystone
Crop circles first drew attention in the mid-1970s, when they were photographed from the air in fields in Wiltshire County, England, known for being the center of the phenomenon. In the photo above, people investigate a crop circle in a cornfield in Corcelles-pres-de-Payerne, Switzerland, on July 7, 2007.
Photograph by Robert Harding, Getty Images
These gigantic works of art are produced by humans, who pull planks attached to ropes. Despite all of the evidence, many people still think crop circles are the work of something paranormal.
Photograph by Ho New, Reuters
In 2002, a flower-shaped crop circle materialized overnight in a wheat field in London's Kew Gardens (seen here on September 19, 2002), forcing the garden staff to postpone the harvest.
Photograph by Ron Russell, Photolibrary
Made mainly from flattened cereal crops such as wheat and barley, the earliest examples of crop circles were fairly simple in design.
Photograph by English Heritage, Photolibrary/RCHME
Each year, more than one hundred formations appear in the fields of southern England. Over the last 25 years, the formations have evolved into huge designs with multiple circles and shapes.
Photograph by Tim Wimborne, Reuters
Crop circles have become popular tourist attractions. Tens of thousands of people visit the U.K. each year just to look at them.