When The next we hear of Kassiani is that in 843 she founded a monastery in the west of Constantinople, near the Constantinian Walls, and became its first [[abbess]]. <ref>[http://home.infionline.net/~ddisse/kassia.html "Other Women's Voices"]</ref> Although many scholars attribute this to bitterness at having failed to marry Theophilos and becoming Empress, a letter from [[Theodore the Studite]] indicates that she had other motivations for wanting a monastic life. It had a close relationship with the nearby monastery of Stoudios, which was to play a central role in re-editing the Byzantine liturgical books in the 9th and 10th centuries, thus ensuring the survival of her work (Kurt Sherry, p. 56).

She wrote many hymns for liturgies; the most famous being the eponymous '''[[Hymn of Kassiani]]''', sung every [[Holy Week}|Holy Wednesday]] (liturgically; actually chanted late in the evening of [[Holy Week|Holy Tuesday]]).