Professional sumo (ōzumō?) roots trace back to the Edo period in Japan as a form of sporting entertainment. The original wrestlers were probably samurai, often rōnin, who needed to find an alternative form of income. Current professional sumo tournaments began in the Tomioka Hachiman Shrine in 1684, and then were held in the Ekō-in in the Edo period. Western Japan also had its own sumo venues and tournaments in this period, with the most prominent center being in Osaka. Osaka sumo continued to the end of the Taishō period in 1926, when it merged with Tokyo sumo to form one organization. For a short period after this, four tournaments were held a year, two tournaments in locations in western Japan such as Nagoya, Osaka, and Fukuoka, and two in the Ryōgoku Kokugikan in Tokyo. From 1933 onward, tournaments were held almost exclusively in the Ryōgoku Kokugikan, until the American occupation forces appropriated it and the tournaments moved to Meiji Shrine until the 1950s. Then, an alternate location, the Kuramae Kokugikan near Ryōgoku, was built for sumo. Also in this period, the Sumo Association began expanding to venues in western Japan again, reaching a total of six tournaments a year by 1958, with half of them in Kuramae. In 1984, the Ryōgoku Kokugikan was rebuilt and sumo tournaments in Tokyo have been held there ever since.