The rabbinic account of the founding of Yavneh is a story about a request made during a siege. Yohanan ben Zakkai, opposing the war party inside Jerusalem, had himself carried out of the city in a coffin, was brought before Vespasian, greeted him as emperor, and when word arrived that he had been proclaimed, was granted a favour. He asked for Yavneh and its sages. The story appears in several versions with different details and is told long after the events, so it works as a charter for what followed rather than as reportage, and later rabbis argued about whether he should have asked for Jerusalem instead. What is clear is that a court and a school operated at Yavneh after 70 and that they acted with authority. The measures attributed to them, the takkanot, take practices that had belonged to the Temple and relocate them: the ram's horn may be sounded on a sabbath in the town where the court sits, the palm branch is taken all seven days everywhere, the priestly blessing is said in the synagogue.
Under Gamaliel II the court claimed the right to fix the calendar, which is the practical core of religious authority, and the standard order of the daily prayer was settled there. The court also settled matters that a modern reader would not expect a religious body to touch, including the legal status of a woman whose husband had disappeared, which mattered enormously after a war that had left many such cases. That combination, ritual, calendar and civil law in one body, is what made Yavneh the model for the rabbinic academies that followed it.