The Role of the Sanhedrin according to the Mishnah

A tribe, a false prophet, or the high priest may not be tried except by the court of seventy-one. They may not send forth the people to wage a battle of free choice save by the decision of the court of one and seventy. They may not add to the city [of Jerusalem] or the courts of the Temple except by the decision of the court of seventy-one. They may not set up Sanhedrins for the several tribes except by the decision of the court of one and seventy. And they may not proclaim [any city to be] an apostate city [see Deuteronomy 13:13–19] except by the decision of one and seventy. No city on the frontier may be proclaimed an apostate city, nor three together, but only one or two.