In a Bosnian wood, the discovery of a strange giant sphere has sparked debate after a researcher claimed that it could be evidence of an ancient civilization.

Archaeologist Semir Osmanagich estimates that the sphere— which resembles a giant cannon ball protruding from an embankment—could have a diameter of anywhere from 7 to nearly 10 feet.

The coloring of the sphere suggests a high iron content, Osmanagich says, meaning it could weigh more than 30 tons.