Halakhah for Sanhedrin 32:3

To appoint judges and officers: To appoint (see Sefer HaMitzvot LaRambam, Mitzvot Ase 176) judges and officers that coerce [others] to do the commandments of the Torah, bring those that are veering from the path of the truth back to it against their will, order that which is fitting to do, prevent disgusting things and enforce the fences against the transgressor - so that the commandments and the preventions of the Torah not require the belief (acceptance) of each and every person. And it is from the conditions of this commandment that these judges should be one level above the other. That is that we set up twenty-three judges in each and every city that is fit for this number, all gathered together in one place from the gates of the city - and that is called a small sanhedrin. And in Jerusalem, we set up a large court of seventy judges, and we stand up one [judge] over these seventy and he is called the head of the academy - and he is the one that the Sages also called, nassi - and they would all be gathered in their place that is designated for them. And in a place that is small of number, such that it is not fit for a small sanhedrin, they should stand up three [that] should judge the small thing and they bring the difficult thing to the [court] that is above them. And likewise do they appoint supervisors among the people that circulate in the city, the markets and the streets [and] observe the matters of people in commercial buying and selling - so that there not be wrongdoing, even with a small thing. And the commandment that comes about this is that which He, may He blessed, stated (Deuteronomy 16:18), "Judges and officers shall you place for yourself in all of your gates." And the language of Sifrei Devarim 144 (and see Sanhedrin 16b), "From where [do we know] that we appoint a court for all of Israel? [Hence] we learn to say, 'Judges and officers.' And from where [do we know] that we appoint one [judge] on top of them all? [Hence] we learn to say, 'shall you place for yourself.' And from where [do we know] that we appoint a court for each and every tribe? [Hence] we learn to say, 'in all of your gates.' Rabban Shimon ben Gamliel said, '"For your tribes and they shall judge" - [that] is a commandment on each and every tribe to judge its tribe; "and they shall judge the people" - against their will.'" And this commandment to appoint seventy elders has already been repeated, and that is His, may He be blessed, stating to Moshe, peace be upon him, "Gather for Me seventy men" (Numbers 11:16). And they, may their memory be blessed, said (Sifrei Bamidbar 92), "Every place that it is stated, 'for Me,' behold it is an observance forever; and so [is it], 'And they shall be priests for Me, etc.' (Exodus 28:41)" - meaning to say, that it is a permanent commandment and not just temporary, but rather all of the days of the earth.