Inside the church
In its interior, the church has preserved all of the architectural elements from the sixth century. When he first saw the actual project, the Byzantine emperor did not approve the choices made by the architect, accused him of having squandered the funds, and ordered that he be beheaded. Despite the emperor´s dissatisfaction, the building has shown itself to be very solid, surviving intact until the present day.
Excavations carried out by the British government in 1932 showed that the Constantinian-era floor had been completely covered over with finely-crafted mosaics displaying geometric and floral decorations.
Among these is to be highlighted the mosaic remnant preserved to the west of the presbytery, where by raising the wooden trapdoor one can see the monogram ΙΧΘΥΣ (“fish” in Greek) used in ancient times to indicate the name of Christ. While today the floor consists of a simple rough stone pavement, the Byzantine-era floor had white marble slabs whose veins were particularly accentuated. A remnant of this can be seen in the area of the north transept.
The Constantinian pavement was slightly inclined relative to the current floor, which is about a meter above the original level. The internal space, divided by columns into a nave and four aisles, is dark and dimly lit. In the sixth century the church was completely covered in marble: traces of the holes used to attach the marble can still be seen in the re-plastered walls.
The colonnade, which today finishes at the end of the area of the apse, carried on, creating an ambulatory around the Grotto of the Nativity. This type of architectural structure was used in a number of Holy Places, especially those for Martyrs, because, according to tradition, pilgrims who walked repeatedly around the holy site would in this manner obtain grace. The columns and capitals, made from red stone from Bethlehem, are the original ones from the Byzantine period, the product of local craftsmen. The capitals, works of exquisite craftsmanship, were painted in blue. On the columns were representations of a number of Eastern and Western saints, both religious and lay. The architraves are also from this period, although their adornment goes back only to Crusader times and is very similar to that of the architraves in the Church of the Holy Sepulchre, which also date from this latter period. The high walls of the nave are decorated with superb mosaics dating from the 12th century, the works of Eastern masters.
The mosaics are divided into three groups and show, starting from the bottom: the genealogy of Jesus, the councils and local synods and, at the top, a procession of angels. According to a Greek account from the ninth century, earlier there had been additional mosaic decorations dating from the Byzantine period.
Among these special note was made of the representation of the Magi who arrived in Bethlehem to adore Jesus, which adorned the façade. A truly singular event occurred in 614 AD when the Persian soldiers who were invading the town took fright at the sight of the mosaic and renounced their intention to sack the church, which thus escaped unscathed.
The transepts, which still preserve the original marble pavement from the Byzantine period, are today decorated with icons and vestments from the Greek Orthodox (right transept) and Armenian Orthodox (left transept) traditions. This part of the church also preserves mosaic decorations skillfully portraying scenes from the Gospels.