The manuscripts made in Rome during the sixteenth century, often unknown and reduced to a stylistic study, have a complex relationship with the artistic context of the period. Rome brings together a number of artists whose origins and training permeate the local idiom, leading to exceptional creations. Giulio Clovio, Vincent Raymond, Jacopo del Giallo and Apollonio di Bronfratelli insert in their miniatures not only the motifs of the monumental decorations. They also adapt the principles of the ornament to the fields of the manuscript decoration. The illuminated manuscript is transformed into a field of experimentation where the ornament embodies various artistic problems. Unexpected agents during the act of reading, the decorative figures also participate in the actualization of meditative reading, thus proposing a new conceptualization of medieval ruminatio. Reporting on both private and official commissions, the study of these illuminations will give rise to observations concerning the function of ornamentation according to the context and the type of use. Through a semiological approach and a systematic study of the production of the period, this research proposes to fully integrate the illuminated book into the artistic universe of the Italian sixteenth century.