Judo, translated "the gentle way," has its roots in the ancient art called jujutsu. Modern judo as we know it today was organized by Kano Jigoro. He established the Kodokan school of judo in 1882 and formulated a training system based on modern athletic principles. He also modified the rules to permit both throwing and grappling on the mat. During a match, regulation uniforms known as judo-gi are worn by judo wrestlers. The floor space where the match takes place is exactly14.55 meters square, with a 9.1 meters square center area on which the wrestlers compete. There are three categories of techniques used by the judo wrestlers; nage-waza (throwing), katame-waza (grappling), and atemi-waza (attacking vital points). There is a ranking system in judo that reflect the wrestler's ability. The highest rank is the 10th-dan, and the lowest is the shodan. Below shodan are the kyu, 1-kyu being the highest and 5-kyu being the lowest. Matches are organized both by weight class and a single all-weight class. Judo has become an internationally popular sport, practiced by over five million people. In 1951, the International Judo Federation was established, with over 120 nations represented today. The first World Judo Championship Tournament was held in 1956 in Tokyo. Judo became an Olympic sport in 1964.