rabbinical schools opened a new era for diaspora Judaism, and the ensuing discussions in their classes furnished the earliest stratum and style of the scholarly material deposited in the Babylonian Talmud. The coexistence for many decades of these two colleges of equal rank, even after the school at Nehardea was moved to Pumbedita (now Fallujah), produced for the first time in Babylonia the phenomenon of dual leadership that, with some slight interruptions, became a permanent fixture and a weighty factor in the development of the Jewish faith today. The key work of these semi-competing academies was the compilation of the Babylonian Talmud (the discussions from these two cities), completed by Rav Ashi and Ravina, two successive leaders of the Babylonian Jewish community, around the year 520, though rougher copies had already been circulated to the Jews of the Byzantine Empire. Editorial work by the Savoraim or Rabbanan Savoraei (post-Talmudic rabbis), continued on this text's grammar for the next 250 years; much of the text did not reach its "perfected" form until around 600–700 AD. The Mishnah, which had been completed in the early 3rd century AD, and the Babylonian Gemara (the discussions at and around these academies) together form the Talmud Bavli (the "Babylonian Talmud"). The Babylonian Jews became the keepers of the Bible. Jewish culture flourished in Babylonia during the Sasanian Empire (331–638) and catalyzed the rise of Rabbinic Judaism and central texts. Jewish scholars compiled the Babylonian Talmud starting in 474 as the spiritual codex of Judaism, transferring Judaism into a spiritual and moral movement. The Talmud, a central commentary on the Mishnah, was perceived as a "portable homeland" for the Jews in diaspora. The three centuries in the course of which the Babylonian Talmud was developed in the academies founded by Rab and Samuel were followed by five centuries during which it was intensely preserved, studied, expounded in the schools, and, through their influence, discipline and work, recognized by the whole diaspora. Sura, Nehardea, and Pumbedita were considered the seats of diaspora learning; and the heads of these authorities were referred to later on as Geonim and were considered the highest authorities on religious matters in the Jewish world. Their decisions were sought from all sides and were accepted wherever diaspora Jewish communal life existed. They even successfully competed against the learning coming from the Land of Israel itself. In the words of the haggadist, "God created