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The Rambam in Hilchot Kiddush Hachodesh 4:5 (Thanks @DonielF) states that Sanhedrin was allowed to declare a leap year not just based on "seasonal alignment' (I.e. 16 Nissan should be after the spring equinox.)

They could declare a leap year if the roads / bridges were washed away during the rainy season and if it would be too difficult to get to Yerushalayim for the pilgrimage. There were other reasons as well.

Was there a limit to how many consecutive years that Sanhedrin could declare a leap year? Were there any documented cases when Sanhedrin declared a leap year for 2 or more consecutive years?

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  • If you have an internet connection you have all of Rambam's works in front of you. Searchable too. – Double AA♦ Mar 29 at 16:50
  • @DoubleAA Thanks. I'm restricted from accessing most "religious sites" at the moment. – DanF Mar 29 at 16:52
  • Obviously you can’t have this in our calendar, where they’re spaced out every 2-3 years, but an intriguing question for pre-Hillel times. +1 – DonielF Mar 29 at 17:17
  • The Halacha you’re looking for is Kiddush HaChodesh 4:5, from Sanhedrin 11b, by the way. – DonielF Mar 29 at 17:19
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    @DanF It’s my understanding of Shevili d’Rakia that the eighth year technically is unnecessary. The issue is the following year would be way too early, so we counterbalance it by making that year a leap year even though it doesn’t need to be. (Ditto for the nineteenth year.) I know that seasonal drift is an issue, but it doesn’t seem to have added up to anything too problematic just yet. – DonielF Mar 29 at 18:51
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Depends who you ask. The Gemara, Sanhedrin 12a, says:

אין מעברין את השנה לא משנה לחברתה ולא שלש שנים זו אחר זו אמר רבי שמעון מעשה ברבי עקיבא שהיה חבוש בבית האסורים ועיבר שלש שנים זו אחר זו אמרו לו משם ראיה ב"ד ישבו וקבעו אחת אחת בזמנה

The court may not intercalate the year from one year to another, and it does not intercalate three successive years, one directly after the other. Rabbi Shimon says: There was an incident involving Rabbi Akiva at the time when he was incarcerated in prison, and he intercalated three years, one after the other. The Sages said to Rabbi Shimon: Is there any proof from there? Rabbi Akiva merely made the calculations, but a special court sat and established each one at its time.

Rashi there (first explanation) says that the question is actually about whether you can have three consecutive leap years, with the Tanna Kamma saying no and R' Shimon saying yes. According to that explanation, the maximum would be 3 according to R' Shimon and 2 according to the Chachomim.

But Tosafos there finds that explanation difficult, since two consecutive leap years would also put the Yomim Tovim out of season, and so they prefer Rashi's second explanation, that the question is how many future leap years they can plan ahead for at one time. In that case, it sounds like there could never be even 2 in succession.

Rabbeinu Chananel there seems to understand somewhere in between: everyone agrees you can have 3 consecutive leap years, and the argument is just whether those can be predetermined or whether they have to declare each one in its time. He gives a scenario in which you could have three consecutive leap years: suppose that in the 14th year of the machzor (which is supposed to be a leap year) there was a famine, the 15th was Shmita, and the 16th is the year after Shmita (and the Gemara there earlier says that you're not supposed to declare a leap year in such cases). Since there still need to be 7 leap years in every 19, that means they'd need to make years 17-18-19 all leap.

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  • Very interesting. I may have to view the Gemarah to get a better sense of things. For now, one question - "Since there still need to be 7 leap years in every 19" - This confuses me, as I understood that the whole concept of the 19 year cycle was established only after Hillel 2. If Sanhedrin declared leap years at spur of the moment, why would they need a "cycle"? – DanF Mar 29 at 20:37
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    @DanF The formal 19-year cycle was set up in Hillel's times, true. But (1) it was known earlier too (see Rambam, Hilchos Kiddush Hachodesh 5:2), and (2) practically speaking, that cycle best approximates the differences between the solar and lunar cycles, so I guess Rabbeinu Chananel assumes that they followed it back then too. – Meir Mar 29 at 20:45

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