A dohyō (, ) is the space in which a sumo wrestling bout occurs. A typical dohyō is a circle made of partially buried rice-straw bales 4.55 meters in diameter. In official professional tournaments (honbasho), it is mounted on a square platform of clay 66 cm high and 6.7m wide on each side. Configuration and construction In professional sumo, a new dohyō is built prior to each tournament by the yobidashi (ring attendants), who are responsible for this activity. The process of building the dohyō and its 66 cm high platform takes three days and is done with traditional tools. The clay used is taken from the banks of the Arakawa River in Saitama Prefecture. However, due to growing urbanization, clay from Ibaraki Prefecture has started to be used. The surface is covered by sand. The dohyō is removed after each tournament and in the case of Nagoya, pieces are taken home by the fans as souvenirs. The yobidashi also build the dohyō for training stables and sumo touring events. The diameter of the ring is 15 shaku (4.55 meters), which increased from 13 shaku (3.94 meters) in 1931. The rice-straw bales (tawara (俵)) which form the ring are one third standard size and are partially buried in the clay of the dohyō. Four of the tawara are placed slightly outside the line of the circle at the four cardinal directions, these are called privileged bales (tokudawara). Originally, this was to allow rain to run off the surface, when sumo tournaments were held outdoors in the open. Today, a wrestler under pressure at the edge of the ring will often try to move himself round to one of these points to gain leverage in order to push back more effectively against the opponent who is trying to force him out. At the center are two white lines, the , behind which the wrestlers must position themselves at the start of the bout. First introduced in the spring tournament of 1928, they are painted 90 cm long, 6 cm wide and 70 cm apart. The shikiri-sen are touched up by yobidashi at the end of each day with white enamel paint. The painted lines are notably slicker than the surrounding dirt, but rarely cause a wrestler to slip due to their narrowness. Around the ring is finely brushed sand called the ja-no-me (蛇の目, snake's eye), which can be used to determine