These days, modern sumo hasn’t changed much since the original Edo period, and to watch a sumo match today is to watch centuries of Japanese history in motion. Rules, Rituals & The Ring. Sumo bouts are held in a ring called a dohyo. A modern dohyo is a circular area, 4.55 meters wide, made of rice-straw bales and mounted on a square clay platform. The tops of the bales are covered in a thick layer of sand, which forms the wrestling surface.