In several southeastern Illinois counties there exists collections of large boulders that, often, seem out of place with the surrounding landscape. Scientists have determined that these pre-date the fall of the Roman Empire. Who built these? How and why were they built? We are not certain, and Carrier Mills history teacher Mark Motsinger has been studying these mysterious stone walls and is in the process of writing a book about these structures. Here is Mark talking with WSIU's Kevin Boucher about these.