when reluctance to write down rulings became obsolete, letters of a legal nature might be written only in cases where laws might likewise be reduced to writing. While the rule prevailed that no laws should be written, no communications of legal content were made by means of letters. Questions were usually communicated orally, or proposed to the academy by a teacher, who transmitted the answer and decision by word of mouth. The rarity of letters on legal problems in the Tannaitic era (the period the Mishnah covers) may be seen from a passage in the Tosefta, which states that Rabbi Gamliel secretly dispatched a messenger with an answer to a question; for if he desired to keep his decision secret, he would probably have sent a letter had such replies been customary at that time. Mishnaic era In the Tannaitic period (100 BCE to 200 CE) statements, publications, contributions concerning the calendar, and notifications were the only documents regularly committed to writing. On the other hand, it can not positively be asserted that no ruling at all had been given in writing before the completion of the Mishnah: certain exceptions were doubtless made. In the Talmud Immediately after the completion of the Mishnah, when the prohibition or reluctance against writing halakhot had in great part disappeared, the responsa literature began to appear, traces being preserved in the Talmud. Often questions were settled by a single letter, as was later the case with the Geonim, who exchanged a series of responsa. The replies were signed by pupils and colleagues, so that, strictly speaking, the responsa were issued by a board. With the beginning of the third century of the common era, responsa begin to frequently appear in letters from Babylonia to Israel. By the end of the third century the correspondence between Israel and Babylonia had become more active, and the responsa from the one to the other had become far more numerous. These rulings from rabbis in Israel seem to have been regarded as authoritative and demanding obedience; and the threat was made to Rabbi Judah ben Ezekiel, head of the Academy of Pumbedita, that a letter would be brought from "the West" (i.e., Israel) to annul his decision. The same experience befell and Mar Ukba and another, unnamed, judge. Geonim During the Geonic period (650–1250 CE), the Babylonian schools were the chief centers of Jewish learning; the Geonim, the