bet din but not a rav

In my Sunday Rambam chabura, we’re up to hilchot Sanhedrin. I’ve been
suggesting trying to deconstruct the halachot to understand the underlying
theories (of HKBH and chazal-eg predilection to not convict the innocent
and why). When the Rambam (Hilchot Sanhedrin 1:10) lists the role of the
120 people required in a town to have a Sanhedrin, I noted there is a bet
din but not a rav. It appeared to me that historically(certainly Talmudic
times) the leadership focus was on the be din and sometime/somewhere it
reversed. If so, any idea when and (to me more importantly) why?
KT
Joe; Rich

Actually, he says it's a requiement of the Sanhedrin, not the town.

You cannot convene a Sanhedrin in a town that didn't have 120 -- I presume
120 Jewish adult men. But that doesn't mean that towns were obligated
to have courts.

And going back to shas is problematic, because back then there were
both real semichah and the authority to levy kenasos and to mete out
the standard misos beis din.

Thinking out loud:
Maybe today's obligation to have courts can be statisfied with just a
rabbi who hopefully knows what he is doing, as long as he can always
find two hedyotos as the other dayanim if a case comes up.

Tir'u baTov!
-Micha