Pope Gregory the Great is one of the prominent Christian authors transmitted in the medieval manuscripts in the Biblioteca Capitolare in Piacenza. Among the 84 codices in this library one of the oldest contains his Regula pastoralis and another from c. 1215 the Moralia in Iob, but his authorship is especially represented in the twelfth-century sources for the celebration of both the mass and the divine office of the episcopal liturgy, revised in the wake of the Gregorian reform in the late 1070s.

In my contribution I analyse some mass chants in the Graduale part of the liturgical totum codex 65 from 1142, also known as the Liber magistri, e.g. the non-biblical introit antiphon Gaudeamus in domino which Gregory is said to have composed for the re-dedication of the former Arian church Agatha dei Gothi in Rome in 592, and the texts for the celebration of his feast-day on March 12, as well as various aspects of the liturgical use and reception of a large number of his homilies, especially the Homiliae in Euangelia, and some of the hagiographical texts from his Dialogi that had been selected and assigned as lessons in the full lectionary for the divine office.