Thesis (Ph.D.) - Indiana University, Department of Art History, 2023The Breviary of Saint-Sépulcre (Cambrai bibliothèque municipale MSS 102 and 103) actively participated in liturgical performance and contributed to spiritual experience at the abbey of Saint-Sépulcre in Cambrai in the late thirteenth and early fourteenth centuries. This project explains what its contributions were by uniting careful attention to the individual manuscript with a study of one hundred seventy-one other books connected to it by artists' hands, the monastery's library, or by contemporary use in neighboring Benedictine institutions. By analyzing signs of use like dirtied margins and rubbed images, alongside the location and iconography of the illustrations appearing in the monastic breviaries in this corpus, this study demonstrates that liturgical manuscripts like the Breviary of Saint-Sépulcre were simultaneously supports for corporate devotion and spaces for private contemplation. The images in the breviary's margins functioned as mechanisms for affecting difficulty, a response capable of uniting thought and action, deepening and extending the spiritual and intellectual experience of the liturgy, and guiding the manuscript's reader-viewer to enact their monastic community's ideals. The images accomplished this by requiring extended effort and offering opportunities to be tempted and to fail. This in turn encouraged compunction and the cultivation of humility which turned the reader-viewer toward their community and their god. In this way, profane and obscene marginalia in the Breviary of Saint-Sépulcre and liturgical books like it are newly cast by this dissertation as devotional images. No mere technology of the book, ornamentation required by period style, or artistic whimsy, marginalia are difficult images—and they were key to the performance of the Breviary of Saint-Sépulcre.