Starting from the concept and definition of littera in the Grammar treatises of the Late Antiquity and the Early Middle Ages, the contribution analyzes common graphic elements which were used by the scribes to create initials, ornamental patterns and the layout of the manuscript page. These elements and their functions were partly described in encyclopaedic works, e. g. of Isidor of Sevilla and Martianus Capella in the chapters about Geometry. Not only were these features well known through the study of (...) the Artes, they also represented useful tools for the invention and production of medieval diagrams. (shrink)