This chapter provides the first attempt at a comprehensive survey of the diagrams attached to the so-called Corpus Hermogenanium. Found mostly in the margins of the manuscripts of the Corpus, diagrams visually complement the handbook as well as the collections of commentaries examining it: they provide a schematic representation of sections and/or definitions featuring in the text so as to clarify and summarize them. A preliminary grouping of the diagrams based on the relationships they express will show, on the one hand, their wide application in the Corpus and, on the other, their variability. The analysis of a case study, additionally, will prove that not only did diagrams supplement the study of rhetoric but also actively contributed to its long-term process of reconceptualization unfolding in the Middle Byzantine period.