Crop circle

Crop circles were occurrences where shapes would be made from flattened crops. They were generally thought to be a sign of alien activities.

Maxwell Edison was investigating a crop circle in Stockbridge before being caught up in an adventure with the Eighth Doctor. (DWM: End Game)

A crop circle was seen in Kent. It was noticeable for being made of square-sided shapes and being filled with ice. (PDA: The Algebra of Ice)

In 2011, Amy Pond and Rory Williams made a crop circle with their car in an attempt to attract the attention of the Eleventh Doctor. (DW: Let's Kill Hitler)