Kassiani was an Eastern Roman abbess, poet, composer, and hymnographer. She is one of the first medieval composers whose scores are both extant and able to be interpreted by modern scholars and musicians. Approximately fifty of her hymns are extant and twenty-three are included in Orthodox Church liturgical books. The exact number is difficult to assess, as many hymns are ascribed to different authors in different manuscripts and are often identified as anonymous.
-from Wikipedia – https://en.wikipedia.org/wiki/Kassiani