Ulla עולא
travelled between the land of Israel and Babylonia, carrying learning across
Ketubot 111a says that Ulla was in the habit of going up to the land of Israel from time to time — and that he died outside it after all; his body was brought back and buried in the Land.
Such men are called nechutei in Talmudic scholarship — "those who go down": they travelled from the land of Israel to Babylonia and brought the teaching of the schools there. The word itself does not appear in this passage, but the role is described exactly.
The importance of that work shows in the structure of the Babylonian Talmud, which is full of formulas of the type "when so-and-so came, he said: thus they say in the West." Without constant communication between the schools, Babylonian and Palestinian learning would have parted for good.
His too is the famous line quoted in his name by Rabbi Chiya bar Ami in Berakhot 8a: since the day the Temple was destroyed, the Holy One has nothing in His world but the four cubits of halakhah. It is quoted constantly, and almost always without saying whose words they are.
On the timeline
Sources
Chazal: Mishnah, Talmud, midrash, Zohar
- Ketubot 111a — the ascents to the land of Israel, and death outside it
- Berakhot 8a — “the four cubits of halakhah” — in Ulla's name
Basis: Talmud and midrash.