Sumo is the official national sport of Japan, as recognized by the country's government. It is built around the simple concept of two nigh-naked men battling within a small roped ring, but actually has a far deeper meaning, which encompasses both Shinto beliefs and Japan's most subtle cultural nuances. Historical records have the sport dating back at least 1500 years, with popular myths linking the sport to events even further back than that. Professionalized in the 18th century, sumo continues to thrive in the present-day, staging six tournaments a year with the average weight of competitors around 140 kilograms (308 lbs).