Zenith lighting in Christian places of worship between reality and fiction (West-East, 4th-13th centuries)

This article analyses the light irradiation from the top in the places of worship of medieval Christianity, whether as phenomenon of natural origin, produced by an oculus, or figuratively, through the creation of two-dimensional medallions at the summit of the vault. Few but significant examples refer to the first aspect of the question, such as the Rotunda of the Anastasis and Santa Maria ad Martyres (Pantheon). The image of the zenithal light, instead, often occurs inside the coverings of the domes, especially in the mosaic decorations (Santa Costanza, Baptistery of the Orthodox, Rotunda of Saint George, etc.). In these and other contexts, the effect of a circular window open at the top of the vault is suggested by the iconographic theme, which evokes the vertical motion of transcendence, ascendant (Resurrection and Assumption) or descendant (Pentecost, Baptism, Second Coming), and through the fake frames or particular colour combinations (gold/silver, gold/blue, degrading shades from blue to white, rainbow bands). Both in the physical manifestation and in the iconographic representation, the light from above plays a central role in some medieval rituals related to the celebration of Baptism, Pentecost and Resurrection.