The common punishments meted out by the Jewish court are malkot (lashes) and occasionally mitat beit din (capital punishment) for severe crimes. Incarceration in prison, the most common form of punishment today, was unknown to the Sages. Nevertheless, there was a type of prison known as a kippa (vaulted chamber) that the Mishnayot on today’s daf discuss.
The Mishna teaches that if someone murdered his fellow and there were no witnesses (as the Gemara explains, there were witnesses but their testimony was rejected for technical reasons), the court will place the accused in a kippa and feed him bread and water. Similarly, the Mishna teaches, someone who repeatedly commits crimes and is punished is also placed in a kippa where he is fed barley until his stomach bursts. The Gemara explains that we are talking about someone who repeatedly committed crimes for which the punishment is karet – a death sentence left to God. As Rabbi Yirmeya explains in the name of Reish Lakish, since his activities show that he has given up on his life, the court assists him in bringing his life to an end. The Gemara further explains that in both of these cases he is first fed bread and water and then he is fed barley, a diet that will hasten his death.
Rav Yehuda explains that a kippa is a small and narrow prison. According to Reish Lakish, the source for this punishment is found in (34:22) where we find that the end of an evildoer is an unpleasant death.
The discussion among the rishonim is whether the institution of kippa is an oral tradition from Moshe and works on a biblical level or if it is a rabbinic regulation that was established in order to give the Jewish courts a method of dealing with anti-social behaviors that cannot be prosecuted under the strict laws of the Torah. Such an approach is particularly appropriate in cases of setting a murderer free, where the concerns for society may obligate the courts to act.