ABSTRACT
This introductory chapter begins with a discussion of the importance of the threshold of heaven, or porta coeli, for the medieval world. Christ first described himself as the “gate of heaven” in Jn. 10:9, but he also gave the authority to open or close the gate of heaven to his apostles in Mt. 16:18–19. With this inherited role to save or condemn, the medieval pope and the episcopal clergy would eventually claim ultimate political authority on earth. Because of this ecclesiastical authority at the porta coeli, the motif of the gate had layered symbolic meaning in medieval art. The porta coeli was particularly important for the theology, liturgy and artistic patronage of Saint Ambrose of Milan, the patron saint of the city. Ambrose designed a system of physical gates in Milan to work in tandem with his theology of spiritual transformation at the threshold. His spatial theology of the porta coeli continued to be of lasting significance for medieval Lombardy, particularly as it reinforced the authority of the archbishop of Milan and supported the political and spiritual goals of the local reform movement.
