The studies developed by the team of the School of Specialization in Architectural Heritage and Landscape of "Sapienza" University of Rome, concerned the mosaics, mural paintings and coloring have been aimed to the comprehension of the complicated relation between the single analyzed part and the architectural complex. The ”reading” of the current state of the Basilica, i.e. the historical events that made it as we can see today, has been the starting point for the necessary critical to start the restoration project. Mosaics decorated all the walls in the Church of the Nativity. The decorative cycle included a Tree of Jesse on the counter-façade, whereas the provincial councils of Palestine, the seven Ecumenical Councils, a lower band showing Christ’s ancestors and an upper band between the windows with full-length images of angels were put on display in the central nave. The mosaic is made of glass tesserae, gold tesserae, silver tesserae and stone tesserae.