No Horologion (“Book of the Hours”) has survived in the Old Church Slavonic corpus. Since early Russian sources, however, tend to retain South Slavic liturgical traditions, the authors attempt to reconstruct such a book for daily prayer on the basis of Russian manuscripts from the 13th–14th centuries. A key factor in the reconstruction are the so-called kata stichon hymns, an archaic genre of Byzantine hymnography used for night prayer. The authors analyze the text and meter of these hymns, including one hymn originally composed in Slavonic in imitation of the Byzantine genre, and argue that the later Russian sources reflect an Horologion translated in Bulgaria in the late 9th or early 10th century.