The ars dictaminis, the teaching of socially appropriate and stylistically correct drafting of public letters, has so far been regarded as a specialized field of philology in historical research. This study comprehensively tests and demonstrates the historical value of the ars dictaminis for the first time using various methodological approaches. In doing so, the ars dictaminis is interpreted as a direct, almost normative reference to communicative conventions. Using the example primarily of the Italian city communes, the study illustrates the source value of the ars dictaminis, among other things, in relation to value concepts, mentality, and constitutional thinking of the early commune, as well as their efforts for legitimacy. Thus, the ars dictaminis provides insights into the self-image and generally into the functioning of the commune.