The focus of this lavishly illuminated page is a large initial B containing a representation of the Holy Trinity (three persons in one godhead). The text, Benedicta sit sancta Trinitas, introduces the opening of the Introit for Mass on Trinity Sunday, celebrated one week after Pentecost. An illusion has been created by the artist who painted the framing initial to appear three-dimensional. Beyond the initial a landscape recedes as if viewed through an open window. The decoration extends into all four margins that are filled with small miniatures depicting saints (one was left blank). This page is a masterful example of Renaissance manuscript painting with classicizing leaf scrolls, masks, urns, putti, and other decorative motifs fashionable in Italy at the close of the 15th century. It may come from a set of choir books illuminated for Perugia Cathedral.