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Sport involving attack and defense with the fists. In the modern sport, boxers wear padded gloves and fight bouts of up to 12 three-minute rounds in a roped-off square known as the ring. In ancient Greece fighters used leather thongs on their hands and forearms, while in Rome gladiators used metal-studded leather hand coverings (cesti) and usually fought to the death. Not until implementation of the London Prize Ring rules in 1839 were kicking, gouging, butting, biting, and blows below the belt eliminated from the boxer's standard repertoire. In 1867 the Queensberry rules called for the wearing of gloves, though bare-knuckle boxing continued into the late 1880s. The last of the great bare-knuckle fighters was John L. Sullivan. From Sullivan on, the U.S. became the premier boxing venue, partly because immigrants supplied a constantly renewed pool of boxers. Boxing has been included among the Olympic Games since 1904. Today there are 17 primary weight classes in professional boxing: strawweight, to 105 lbs (48 kg); junior flyweight, to 108 lbs (49 kg); flyweight, to 112 lbs (51 kg); junior bantamweight, to 115 lbs (52 kg); bantamweight, to 118 lbs (53.5 kg); junior featherweight, to 122 lbs (55 kg); featherweight, to 126 lbs (57 kg); junior lightweight, to 130 lbs (59 kg); lightweight, to 135 lbs (61 kg); junior welterweight, 140 lbs (63.5 kg); welterweight, to 147 lbs (67 kg); junior middleweight, 154 lbs (70 kg); middleweight, to 160 lbs (72.5 kg); super middleweight, 168 lbs (76 kg); light heavyweight, to 175 lbs (79 kg); cruiserweight, 190 lbs (86 kg); and heavyweight, over 190 lbs. A bout can be won either by knocking out or felling one's opponent for a count of 10 (a KO) or by delivering the most solid blows and thus amassing the most points. The referee can also stop the fight when one boxer is being badly beaten (a technical knockout, or TKO) or he can disqualify a fighter for rules violations and award the fight to his opponent.