doing fairly good work at Azov in 1274.

Jewish scholars frequented celebrated seats of learning in foreign
lands. Before the end of the twelfth century traces of them are to be
found in France, Italy, and Spain. That in the eleventh century Judah
Halevi of Toledo and Nathan of Rome should have been familiar with
Russian words cannot but be attributed to their contact with Russian
Jews. However, in the case of these two scholars, it may possibly be
ascribed to their great erudition or extensive travels. But the many
Slavonic expressions occurring in the commentaries of Rashi (1040-1105),
and employed by Joseph Caro (ab. 1140), Benjamin of Tudela (ab. 1160),
and Isaac of Vienna (ab. 1250), lend color to Harkavy's contention, that
Russian was once the vernacular of the Russian Jews, and they also argue
in favor of our contention, that these natives of the "land of
Canaan"--as the country of the Slavs was then called in Hebrew--came
into personal touch with the "lights and leaders" of other Jewish
communities. Indeed, Rabbi Moses of Kiev is mentioned as one of the
pupils of Jacob Tam, the Tosafist of France (d. 1170), and Asheri, or
Rosh, of Spain is reported to have had among his pupils Rabbi Asher and
Master (Bahur) Jonathan from Russia. From these peripatetic scholars
perhaps came the martyrs of 1270, referred to in the _Memorbuch_ of
Mayence. It was Rabbi Moses who, while still in Russia, corresponded
with Samuel ben Ali, head of the Babylonian Academy, and called the
attention of Western scholars to certain Gaonic decisions. Another
rabbi, Isaac, or Itshke, of Chernigov, was probably the first Talmudist
in England, and his decisions were regarded as authoritative on certain
occasions. These and others like them wrote super-commentaries on the
commentaries of Rashi and Ibn Ezra, the most popular and profound
scholars medieval Jewry produced, and made copies of the works of other
authors.[18]