Following the conversion, Judaism developed genuine institutional roots within the Khaganate. The Geonim of the Babylonian academies (Sura and Pumbedita) corresponded with Khazar Jewish communities, answering questions of halakha. The Cairo Geniza — the great storehouse of medieval Jewish documents discovered in Cairo in 1896 — contains letters referencing Jewish communities in and around Khazar territory. The Kyiv Letter (~930 AD), the oldest known document written in Hebrew script on Slavic soil, is a fundraising letter from the Jewish community of Kyiv with signatories bearing both Turkic/Khazar names and Slavic names — direct evidence of Jewish communities at the interface of Khazar and Slavic worlds. The Khazar court employed Jewish scholars and administrators. The Schechter Letter (another Cairo Geniza document) describes Khazar Jewish history from an internal perspective. While the depth of popular conversion beyond the ruling class is debated, the institutional presence of halakhic Judaism — rabbis, synagogues, Torah courts, community charity structures — in Khazar territory is well-attested in the sources.