After the Torah was given, Moses served as the sole judge of the Jewish people until a judicial hierarchy was established at the suggestion of Jethro, Moses’ father-in-law. One judge was assigned to every hundred men. This judge could appeal, if necessary, to a higher court (a judge over a thousand). Only the most difficult disputes were brought to Moses for adjudication.
While this system was an improvement, it was only the first step in the development of the halachic judicial system. Eventually, the Jewish courts were constructed of three levels:
The Great Sanhedrin was composed of 71 sages and served as both a judicial court and a legislative body.
Little Sanhedrins, each composed of 23 judges, handled capital cases.
The Batei Din (plural for Bet Din, House of Judgement), however, were the most common courts. They dealt with both civil law and religious law. A bet din is composed of three judges and is the only halachic judicial system that still functions today.
The Jewish legal system was an improvement over the common ancient system that consisted of single judges, because it recognizes human fallibility. As Rabbi Ishmael ben Yosi noted (Ethics of the Fathers 4:8): “Do not judge on your own, for there is none qualified to judge alone, only the One [God]. And do not say, ‘You must accept my view,’ for this is their [the majority's] right, not yours.”
Human beings are far too easily swayed: by the tears in a litigant's eyes, by the clothing of the accuser or the title of the defendant, or, God forbid, by outright bribery. Therefore, under the bet din system, even in minor cases, a majority decision is necessary.