The lei tai is an elevated fighting arena, without railings, where often fatal weapons and bare-knuckle martial arts tournaments were once held. "Sanctioned" matches were presided over by a referee on the platform and judges on the sides. Participants would lose if they surrendered, were incapacitated, or were thrown or otherwise forced from the stage. The winner would remain on the stage unless ousted by a stronger opponent. If there were no more challengers, they would become the champion. Private duels on the stage had no rules and were sometimes fought to the death. The lei tai first appeared in ancient China, and in its present form during the Song dynasty. However, ancient variations of it can be traced back to at least the Qin dynasty. Today it is used in Sanshou and Kuoshu competitions throughout the world.