spiritual leaders of the worldwide Jewish community in the early Middle Ages, in contrast to the Resh Galuta (Exilarch) who wielded secular authority over the Jews in Islamic lands. The three centuries in the course of which the Babylonian Talmud was developed in the academies founded by Rav and Samuel were followed by five centuries during which it was zealously preserved, studied, expounded in the schools, and, through their influence, recognized by the whole diaspora. Sura and Pumbedita were considered the only important seats of learning: their heads and sages were the undisputed authorities, whose decisions were sought from all sides and were accepted wherever Jewish communal life existed. Geographic area Jewish sources regularly use the term "Babylonia" when referring to the location of the Talmudic academies in the northern half of Lower Mesopotamia during their activity from the second half of the 6th century to the first half of the 11th century (roughly the time of the Geonim). This region was known to contemporaries as the Sasanian province of Asōristān until the Muslim conquest in 637, after which it becomes known in Arabic as Sawad or al-'Irāq al-'Arabi ("Arabian Irāq"). The term "Babylonia" from Jewish sources has always been an anachronism, as the area they refer to is in no way identical with the by far more ancient empires of Babylonia. The Jewish sources only concentrate on the area between the main two academies, Pumbedita (modern Fallujah; west of Baghdad) in the north, and Sura in the south. Both academies, as well as Nehardea and Mahuza, are situated between, or in the immediate vicinity of, the rivers Tigris and Euphrates. History Background The history of the Jews in Iraq is largely unknown for the four centuries covering the period from Ezra (c. 5th century BCE) to Hillel the Elder (traditionally c. 110 BCE-10 CE); and the history of the succeeding two centuries, from Hillel to Judah the Prince (fl. 2nd century CE), furnishes only a few scanty items on the state of learning among the Babylonian Jews. In the chief source of information about the Babylonian schools, Sherira Gaon referred to those dark centuries in his famous letter: "No doubt, here in Babylonia public instruction was given in the Torah; but besides the exilarchs there were no recognized heads of schools until the death of Rabbi [Judah]." The principal seat of Babylonian Judaism was Nehardea, where there were some