Roller skating, gliding on a hard, smooth, durable surface on skates with rollers or wheels, in recent years has become a popular adult sport. Skates mounted on wooden rollers date from the 1860s, and soon wooden wheels replaced the rollers. The ball-bearing skate wheel was invented in the 1880s. The origin of roller skates is obscure (perhaps they were first used in Holland), but the sport became popular among children throughout the world. When figure skating and dance movements were adopted from ice skating, roller skating gained a large adult following. Numerous roller-skating rinks were built in the United States in the 20th cent., and several roller-skating tournaments are now held annually. Following World War II, the roller derby, a spectator sport involving team competition on banked indoor tracks, gained prominence. Since the 1980s in-line skates, which have their wheels, or rollers, arranged in a single line and afford the skater more stability, have largely superseded the older skates.