A kind of site in the northwest North American Plains which was comprised of stone alignments set in radiating spokes, often with central and peripheral cairns. Medicine wheels served a number of purposes and some are as old as 5500 BP. In southern Montana is a medicine wheel which is a prehistoric relic constructed of rough stones laid side by side, forming a circle 70 feet (20 m) in diameter with 28 spokes leading from the center hub, which is about 12 feet (3.5 m) in diameter.