English summary: Starting with a detailed iconographic analysis of the four angles (gammadia) placed in the four corners of the book covers gifted by the Lombard queen Theodelinda to the basilica San Giovanni in Monza (ca. 600 a. D.) the study tries to reconstruct the historical process that led to the development of the book cover as a mirror of its content in early Christian art and established the four gospel codex as a medium representing...