In Greek art of the Archaic period, centaurs are depicted in three different forms. Some centaurs are depicted with a human torso attached to the body of a horse at the withers, where the horse's neck would be; this form, designated "Class A" by Professor Paul Baur, later became standard. "Class B" centaurs are depicted with a human body and legs joined at the waist to the hindquarters of a horse; in some cases centaurs of both Class A and Class B appear together.