One of the oldest churches in Rome – Santa Maria in Trastevere – has one of the most ‘avant-garde’ mosaic apse decoration in the city’s history. In the turmoil that plagued the papacy in the early twelfth century, Pope Innocent II had created a unique monumental image of the Royal Couple (the adult Christ and his mother). It took more than a century for the mosaic’s striking innovations to be digested and carried forward by Italian artists. In preparation for the auspicious date of 1300 and the founding of the first Holy Year, Cimabue in Assisi, Torriti in Santa Maria Maggiore, and finally Cavallini in Santa Maria in Trastevere, demonstrated their response to the earlier mosaic, and their equally ‘avant-garde’ amplifications of its visual motifs and theological ideas. Cavallini, moreover, worked in concert with an aristocratic churchman, literary expert, poet, and brother of the patron of his mosaics. The Cardinal Jacopo Stefaneschi provided six three-line hexameter poems – one for each scene in the Marian cycle that circles the apse. Together the artist and the poet devised synchronized units, verbal and visual, that coordinate with the image in the conch above. The aim of this essay is to define these unparalleled occurrences and the relations between them for the first time.