Rav Tzemach bar Paltoi רב צמח בר פלטוי

Rav Tzemach, son of Rav Paltoi Gaon, headed Pumbedita from 4632 (872) until his death in 4650 (890). His father had sat in the same seat thirty years earlier—not the only such case in the chain of the academies' heads, but not a common one.

His chief work grew out of an ordinary question. A community needed the obscure Aramaic words of the Talmud explained, and instead of a letter Rav Tzemach made a book: some three hundred words in alphabetical order, and with them the names of people and places that occur in the Babylonian Talmud. This is the first talmudic dictionary, and the whole genre descends from it, down to the Arukh of Rabbi Nathan of Rome two centuries later.

The book itself has not survived: we know it from the citations of those who held it. The reason it was needed can be seen without it: the Aramaic the Amoraim spoke had become, by the ninth century, a foreign tongue to the communities, and the Talmud began to need translating out of itself. Much of the Geonim's work is the building of that bridge.

His responsa survive too: on the estate of a man who died in Kairouan whose heirs lived in Spain, and on a woman who had lost her ketubah. Letters like these show how far the reach of the Babylonian academy went.