Since the epoch of the Great Sanhedrin, there has been no central authority recognised throughout Jewry. The Jewish organisation has long been congregational. Since the fourth century there has been no body with any jurisdiction over the mass of Jews. At that date the Calendar was fixed by astronomical calculations. The Patriarch, in Babylon, thereby voluntarily abandoned the hold he had previously had over the scattered Jews, for it was no longer the fiat of the Patriarch that settled the dates of the Festivals. While there was something like a central authority, the Canon of Scripture had been fixed by Synods, but there is no record of any attempt to promulgate articles of faith. During the revolt against Hadrian an Assembly of Rabbis was held at Lydda. It was then decided that a Jew must yield his life rather than accept safety from the Roman power, if such conformity involved one of the three offences: idolatry, murder, and unchastity (including, incest and adultery). But while this decision throws a favourable light on the Rabbinic theory of life, it can in no sense be called a fixation of a creed. There were numerous synods in the Middle Ages, but they invariably dealt with practical morals or with the problems which arose from time to time in regard to the relations between Jews and their Christian neighbours. It is true that we occasionally read of excommunications for heresy. But in the case, for instance, of Spinoza, the Amsterdam Synagogue was much more anxious to dissociate itself from the heresies of Spinoza than to compel Spinoza to conform to the beliefs of the Synagogue. And though this power of excommunication might have been employed by the mediaeval Rabbis to enforce the acceptance of a creed, in point of fact no such step was ever taken.