Iggeret Rav Sherira Gaon: the letter from which we know who followed whom

In 987 the community of Kairouan sent to Babylonia a question that today would be called historical: how was the Mishnah composed, how the Talmud, and in what order did the generations of sages run. Rav Sherira, Gaon of Pumbedita, answered—and answered not in generalities but link by link and year by year.

From this letter we know what the Talmud itself does not supply: the sequence of the Tannaim and Amoraim, who headed the academies and when, when composition ceased and why. Sherira's years run by the Seleucid count and can therefore be converted—a rarity, for there is nothing else by which to date the ancient sages. Ravina's death in 499/500 and the completion of the Talmud come from this letter too.

A further value is its account of how oral teaching became written: Sherira insists that the Mishnah and the Talmud were long transmitted by heart and written down later, and explains how the transmission worked.

The letter survives in two recensions, the "French" and the "Spanish", and they diverge at precisely this point; which stands nearer the original is argued still. Our timeline in its present form could not exist without this letter: nearly the whole chronology of the sages rests on it.