The Time Jews Couldn’t Agree on the Date of Passover

As dissent over an arcane Hebrew calendar concept erupted in the year 921, Jews faced a potential great sin

Elon Gilad
Elon Gilad
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Medieval passover
Seder table in a medieval HaggadahCredit: British Library
Elon Gilad
Elon Gilad

From near and far they had come. Hundreds of representatives of the Jewish communities from throughout the Land of Israel, Egypt, Syria and even as far as Italy, chanting “We beseech Thee, O LORD, save now! We beseech Thee, O LORD, make us now to prosper!” over and over again as they waved willow branches and marched in a procession from Jerusalem’s Priest Gate (we aren’t sure which gate this ancient name refers to) to the nearby Mount of Olives.

It was October 1, 921, Hoshana Rabbah – the seventh day of Sukkot. The crowd assembled around a large stone, believed to be the footstool of God himself, as the head of Tiberias Rabbinic Academy took took his position on it and prepared to talk.

Rabbi Aaron Ben Meir began to deliver his annual sermon, as he had done in the years before. He denounced the hated Karaite sect, thanked the major donors to the academy, announced appointments of new haverim, official representatives of the Geonite in the communities, and announced the length of the months of the coming year.

But this year was different. Aaron Ben Meir announced that the months of Heshvan and Kislev would be short months, 29 days long, while he knew perfectly well that the rabbis at the academies in Baghdad had already announced to their followers that those very same months would have 30 days. This is how the Great Calendar Controversy of 921-2 began.

Once the holiday was over, and the representatives returned to their communities with the news, the realization of what happened set in. Jews were not going to celebrate their holidays on the same days that year.

The Jews of the East, mostly in Babylonia and Persia, who followed the rulings of the Babylonian academies in Baghdad were, for example, going to celebrate Passover on April 14th, while the Jews of the West, in Egypt, Palestine, Syria, Asia Minor and Italy would celebrate the holiday, two days later on April 16th.

Worse, the communities had become intermingled, and in many cities such as Jerusalem and Cairo, there lived Jews belonging to both communities. In these cities some Jews were going to celebrate their holidays on one day, while for others it was just a regular weekday, and then vice versa. This was going to be an embarrassing disaster.

To avoid this a flurry of letters started to circulate throughout the Jewish world, from the communities to the academies, from the academies to the communities, as well as back and forth between the academies. Some of them were preserved in the Cairo Genizah, and from them we know that at the heart of the dispute that stirred Jewry that year was the definition of an arcane Hebrew calendar concept – the Molad Zaken.

Crossing the Red Sea per Exodus 14:21-15:21, from the Rylands Haggadah, illuminated in Spain circa 1325-1350Credit: illuminators of the 14th century

High noon in Babylonia

For the rabbis, both in Iraq and in Palestine, the Molad Zaken took place when the new moon of the month of Tishrei appeared after midday. When this happened – for reasons unknown – the New Year was postponed to the next possible day.

The difference lay in was the definition of “midday” – the cut-off of a Molad Zaken.

The rabbis of Babylonia defined a Molad Zaken as taking place when the new moon appeared on or after the 18th hour of the day (starting the count at sunset the night before), while those of Palestine defined as taking place when the new moon appeared on or after the 642nd part after the 18th hour (an hour consisting of 1080 parts).

This was only a small difference and would usually make absolutely no difference whatsoever.

But the new moon of Tishrei 923 CE was projected to appear on the 237th part after the 18th hour, exactly between the two cut-offs. This meant that the rabbis of Babylonia were going to postpone the New Year by two days to Monday, as the New Year cannot take place on a Sunday, while the rabbis of Palestine were going to leave the holiday on Saturday.

Put otherwise, due to the complicated rules of the Hebrew calendar, the Babylonians needed to add two days to the calendar of the previous year, while the rabbis of Palestine did not. Ultimately this meant that starting with the Passover of 922 C.E., the Jews following the rabbis of Baghdad were going to be celebrating their holidays two years after those who followed the rabbis of Palestine.

Aaron Ben Meir wrote his counterparts in Baghdad beseeching them to order their followers to adhere to his pronouncement, stressing that the calendar had always been under the control of the rabbis of Tiberias. “You know that the early prophets and the sages refrained from intercalating outside the Land (of Israel), and proof of this is Jacob our father” (Translation from Sacha Stern, The Jewish Calendar Controversy of 921/2 CE, Brill, 2019, p. 231). He warned that they were endangering Judaism: “And you, my brothers, hearken, listen, and do not be haughty. Take care of your souls, and of Israel who are dispersed among the nations and who stand on the edge of a sword” (Ibid., p. 245).

In their responses, the rabbis of Baghdad admitted that in the past they followed the rabbis of Tiberias with regards to the calendar, but said that this was no longer necessary: “And to be sure, our rabbis in Babylonia in the earlier generations used to send (letters) and seek from our rabbis of the land of Israel the setting of the months of every year, because they were not expert in the secret of intercalation like them; therefore, they used to write to them.

"But already many years ago, a few sages from Babylonia went up to the land of Israel, and analyzed with the sages of the land of Israel the secret of intercalation, and they scrutinized and researched (it) in the Council, (until) they understood it very well. And now already for many years, they set the months in Babylonia on their own, and also the sages of the land of Israel calculate and set the months on their own, and now, in all these years their calculation has been the same, there has been no difference between them, but rather the calculation is firm and correct, and the festivals are sanctified according to one law and one teaching, because all the calculations were given together by one shepherd. And we have never seen a disruption like this one, or a breach like this” (Ibid., p. 367).

Moses with the tablets (right) and Aaron the High Priest: above is King David playing the harp in a medieval HaggadahCredit: British Library

Inadvertently sinful

Over and over again the rabbis of Baghdad explained to Aaron Ben Meir that he was wrong and that he was causing his followers to “desecrate the festivals of the Lord, and eat leaven on Passover” (Ibid., p. 315). He reminded them that “From our origins until today, favorable mention of you has not left our mouth, and our prayer for you and your honorable elders has been constant, on the Mount of Olives, facing the sanctuary of the Lord, the place of the footstool of God” (Ibid., p. 227).

But neither side budged and indeed it came to pass that the Jews celebrated their holidays on different dates, until, two years later, at the beginning of 924 C.E., the calendars once again converged on their own. Judaism survived.

The problem was to recur in 927 C.E., but we have no indication that a dispute took place. In fact we do not know what happened that year. Did the Babylonians yield to the authority of the rabbis of Palestine? Or was it the other way around? We just don’t know. The next time the new moon of Tishrei appeared between the two cut-offs was nearly 200 years later in 1108 C.E., at this point the academies had suffered such decline that their authority was practically irrelevant.

When the Seljuk Turks took over Palestine in 1071, the rabbis of Palestine went into exile, at first to Tyre and later to Damascus, where their already waning authority fell further until their Geonite ceased to exist. The academies in Baghdad did not fare much better. They gradually lost their relevance over the years as new more prominent rabbinic centers appeared in the West. Donations dried up and sometime during the 11th century the academies were dissolved.

But it was the Jewish Law codified in these Babylonian academies that prevailed in the Jewish world, gradually all communities that had once followed the laws as codified by the rabbis of Palestine either ceased to exist or fell in line with the rest of the Jewish world. Apparently, no one followed the Palestinian rule of the Molad Zaken in 1071 nor any time since.



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