This study compares the building projects, written and epigraphical testimonies, and performative actions of two outstanding figures among fourth century bishops, Damasus and Ambrosius. These monumenta sanctorum worked as catalysts of the emerging cult of the martyrs. Moreover, the different manifestations of episcopal presence, some of which are here examined critically for the first time, illustrate the influence of the two bishops on the process of christianisation in their dioceses, Rome and Milan. Using partly different strategies, they both had a large part in the development and representation of a local Christian history. Their approach in this served as a model for numerous other cities and shaped the Christian cult of the saints into the Middle Ages and beyond.