This chapter explores the development of the tradition around the altar of Saint Maurice that informed letter of canon of Emperor Constantine, and takes as its premise the idea that the basilica functioned as a material expression of evolving traditions and rituals. The manoeuvrings around its architecture, decor and furniture, offer important insights into the ways the liturgical life of Saint Peter's changed and how such changes were justified. Once established and mythologized in the coming centuries, the tradition of the altar of Saint Maurice was perpetuated. In many ways it offers an exemplar for the development of the basilica more generally. From the twelfth century, the imperial coronation ritual became reasonably solidified in the ceremonial texts. Saint Peter's might well be understood as a marble-clad materialization of tradition, its altars expressing the mutations, reconstructions and inventions that that tradition has undergone throughout its history.