Jewish life throughout the world, including the Roman Empire continued to be bound together by several elements which distinguished the Jewish People. They were bound together by their devotion to their faith and to the Torah. None could forget the struggle that was fought by the Hasmonean family and their allies, the Hasidim, to preserve their religious heritage from dilution and contamination by syncretism with Paganism as had been advocated by the Hellenistic priests which led to the Maccabean rebellion.
They considered themselves members of the Jewish nation, Am Yisrael, in Hebrew. The Hebrew language, the sacred language of the Holy Scriptures was the heritage of all Jewish communities. It was called Leshon Ha-Kodesh, the "Holy Language" or “The Language of Holiness." It was cherished and was the basis of fundamental Jewish learning. The Jewish People had complete autonomy; that is, they were governed internally by Jewish Law. So the Jewish legal system, including the Torah and its oral tradition, operated in all centers of Jewish life throughout the world.
The Mishnah, which is the basic constitution of Jewish Law, states in the Tractate Makkot, I:10, that the authority of the Sanhedrin extends to all Jewish communities in the Land of Israel as well as in all the lands of the Jewish diaspora.
The Jewish People always had an operating legal system; that is, a living legal tradition. As we know from the Talmud, every Jewish community had a court of law, and the law was Jewish Law, based on the Torah and its oral traditions. We are further informed that the legal tradition was formalized and decisions were made and administered by the Anshei Knesset Ha-Gedola, the Men of the Great Assembly.
Shimon Ha-Tzaddik is mentioined as being one of the last members of the Great Assembly. He is also quoted as having said:
"The World stands on three foundations: On Torah, on Service (or Labor)
and on Acts of Charity."
The Great Assembly was evidently replaced by the legal system known by the Greek term Sanhedrin. The term Synhedrion in Greek meant a court or a judicial council. The same term was adopted as the designation of the Jewish judicial system so that the Roman authorities --whose language in the eastern provinces was Greek-- would know that Jewish autonomy was governed by the Jewish legal system.
The Pirkei Avot, which is our primary source for these developments, although the data presented are minimal, tells us that the period of the Great Assembly was followed by the period of the Zugot, the "Pairs." This probably represents what later becomes clear when we see that the Chief Judge of the Great Sanhedrin, called the Nasi, is always paired with his colleague who is second to the Nasi, and is known as the Av Beit-Din. Nasi can be translated as "President" or "Patriarch," and means Chief Justice.
Av Beit-Din, which translates as "Father of the Court," can only be understood as Second to the Chief Justice.