Kassia (810?–867?), Constantinople 

Byzantine abbess, composer, and poet. She wrote about 50 Byzantine hymns, 23 of which were included in the official liturgy books of the Orthodox Church (many hymns from this source are still used today). Her most well-known hymn is the Hymn of Kassia, which is sung on the Wednesday of Holy Week (the week before Easter).

Music example:

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