Isaac ben Moses of Vienna, also called Isaac Or Zarua or the Riaz, was among the greatest rabbis of the Middle Ages. He was probably born in Bohemia and lived between 1200 and 1270. He attained his fame in Vienna and his major work, the halachic guide known as the Or Zarua, was very popular among Ashkenazic Jewry. He was a member of the Chassidei Ashkenaz and studied under many scholars, including the Ra'avyah, Rabbi Yehudah HaChasid, the Sar mi'Kutzi and Rabbi Elazar Rokeach. He was among the teachers of Rabbi Meir of Rothenburg. Life In his Or Zarua, the only primary source of information on his life, he mentions two Bohemian scholars as his teachers, Jacob ha-Laban and Isaac ben Jacob ha-Laban. Led by a thirst for Talmudic knowledge, he undertook in his youth extensive journeys to the prominent yeshivot of Germany and France. According to Gross he went to Ratisbon first; but S.N. Bernstein conjectures that previously he stopped for a long time at Vienna, and became closely identified with the city, as he is usually quoted as "Isaac of Vienna." From among the many scholars at Ratisbon he selected for his guide the mystic Yehuda ben Samuel HaChasid. About 1217 he went to Paris, where the great Talmudist Judah ben Isaac Messer Leon became his chief teacher. He also visited for a short time the yeshiva of Jacob ben Meir in Provins. Then he returned to Germany, and studied under the mystic Eleazar ben Judah at Worms, and, at Speyer, under Simchah ben Samuel of Speyer, his intimate friend, and Eliezer ben Joel ha-Levi, author of Abi ha-'Ezri and Abi'asaf. At Würzburg, where Rabbi Meir of Rothenburg was his pupil (c. 1230), he became rosh yeshiva. Later on, Isaac returned to Ratisbon, and then settled for some time in Vienna, where he held the position of Av Beth Din and rosh yeshiva. Finally, he went to Saxony and Bohemia. Isaac lived a long but unsteady and troubled life. He saw the law compelling Jews to wear the yellow badge put into force in France, and he deplored the pogrom in Frankfurt-am-Main (1241) and the extortions practised upon them by the nobles of Austria. His son-in-law was Samuel ben Shabbethai of Leipzig; his son Chaim Eliezer, called Or Zarua, like him a scholar, carried on a comprehensive halachic correspondence, a part of which (251 responsa) was printed under