Sumo Wrestling Terms - Sumo wrestling is a popular sport that dates back many thousands of years. Sumo wrestling is not only the oldest of Japan's various martial arts, it also evolved into the most distinct and ritualistic. It is still heavily centered around the Shinto religion. When the sport was first introduced 1500 years ago it was performed mostly to ensure good harvests. Sumo matches take place in a ring called a dohyo. The dohyo is made of a mixture of clay and sand spread over the top. It is between 34 and 60 cm high. The circle in which the match takes place is 4.55 meters in diameter and bounded by rice-straw bales called tawara, which are buried in the clay. At the center are two white lines, the shikiri-sen, which the rikishi must position themselves behind at the start of the bout. Around the ring is finely brushed sand called the snake's eye, which can be used to determine if a wrestler has just touched his foot, or other part of his body, outside the ring.