Aerial photographs made with hand-held cameras and taken from small aircraft revealed soil discolorations on two sites in Illinois. The light and dark parallel lines were interpreted as evidence of prehistoric agricultural fields. Evidence of houses in the center of these fields was also noted. Ground reconnaissance, controlled surface collecting, and cross-trenching tended to confirm this interpretation. These data were compared with archaeological evidence from Macon Plateau in Georgia and historic records for the Great Lakes region. It is proposed that Mississippian agriculture was based upon a field system and a technique of ridge-furrow cultivation that made it possible to utilize low-lying river bottom land.