Sanhedrin 18 - Size of a Town Fit to Have a Sanhedrin
The town fit for a Sanhedrin must have at least 120 residents: 23 replacements, in case the acting members should all die and need to be replaced, three rows of 23 scholars, ten unoccupied men in the synagogue, two court stenographers, two court officers, two litigants, two witnesses, two people who can discredit the witnesses, and two who can discredit those who discredited the witnesses. Add to this charity collectors, doctor, butcher, and a teacher of children.
The High Priest may judge and be judged. But that is obvious!? You might think that if the High Priest kills inadvertently, he does not go into exile, since accidental killers return from their exile upon the death of the High Priest, and he himself cannot thus benefit. Therefore, the rule says that he is judged nevertheless.
Art: Grigori Grigorevich Chernetsov - Parade on the Field of Mars