Arbaah Turim ארבעה טורים

Rabbi Yaakov, son of the Rosh, wrote in Spain a book that changed the organisation of Jewish law itself. Unlike the Rambam he included only what applies in exile — no laws of Temple or offerings — and divided the material into four turim, «rows», like the rows of stones on the high priest's breastplate.

Orach Chaim: the order of the day, prayer, Sabbath and festivals. Yoreh Deah: kashrut, mourning, interest, and all that «teaches knowledge». Even haEzer: marriage, divorce, family law. Choshen Mishpat: property, courts, damages, commerce.

Its second innovation matters as much: the Tur cites the differing schools — Rambam, Rosh, Rif, Ashkenazi and Sephardi authorities — and says who holds what before ruling. On the Tur, Rabbi Yosef Karo wrote the vast Beit Yosef, out of which the Shulchan Aruch grew with the same fourfold division.