The church of S. Maria in Trastevere was constructed after the Concordat of Worms (1122), at a time when the original ideals of the Church Reform of the eleventh and twelfth centuries were being replaced by a new strategy intended to demonstrate the power of the papacy. The city of Rome and the Church were emerging from a difficult period of conflict culminated in the schism provoked by the double election of Innocent II and Anacletus II as pope, an event that deeply marked the church of S. Maria in Trastevere and its decoration. During the Reform of the Church, significant changes took place in visual language, in its processes of elaboration and creation, as well as in the theoretical debates that reflect the historical, political, and cultural changes that involved all of medieval European society. The apse mosaic of S. Maria in Trastevere provide important evidence to understand this transitional period for the Roman Church.