In defining the commonalities among different stone medicine wheels, the
Royal Alberta Museum cites the definition given by John Brumley, an archaeologist from
Medicine Hat, that a medicine wheel "consists of at least two of the following three traits: (1) a central stone
cairn, (2) one or more
concentric stone circles, and/or (3) two or more stone lines radiating outward from a central point." From the air, a medicine wheel often looks like a wagon wheel lying on its side. The wheels can be large, reaching diameters of 75 feet. The most common variation between different wheels are the spokes. There is no set number of spokes for a medicine wheel to have although there are usually 28, the same number of days in a lunar cycle. The spokes within each wheel are rarely evenly spaced, or even all the same length. Some medicine wheels will have one particular spoke that is significantly longer than the rest. The spokes may start from the center cairn and go out only to the outer ring, others go past the outer ring, and some spokes start at the outer ring and go out from there. Sometimes there is a passageway, or a doorway, in the circles. The outer ring of stones will be broken, and there will be a stone path leading in to the center of the wheel. Some have additional circles around the outside of the wheel, sometimes attached to spokes or the outer ring, and sometimes floating free of the main structure. While alignment with the cardinal directions is common, some medicine wheels are also aligned with astronomical phenomena involving the Sun, Moon, some stars, and some planets in relation to the Earth's horizon at that location. The wheels are generally considered to be sacred sites, connected in various ways to the builders' particular culture, lore and ceremonial ways. Other North American Indigenous peoples have made somewhat-similar
petroforms, turtle-shaped stone piles with the legs, head, and tail pointing out the directions and aligned with astronomical events. == Cultural value, attribution and meaning ==