Fragments of high-quality wall mosaics dating from the 1160s decorate both sides of the nave.
Each side once had three registers, of which we know the details because of a description made in 1628.
The gospel accounts don't mention a cave, but less than a century later, both Justin Martyr and the say Jesus was born in a cave.
The outline of the Justinian square entrance can also be seen above the door.
The wide nave survives intact from Justinian's time, although the roof is 15th-century with 19th-century restorations.
Muslims prevented the application of Hakim's decree (1009) ordering the destruction of Christian monuments because, since the time of Omar (639), they had been permitted to use the south transept for worship. Baldwin I and II were crowned there, and in an impressive display of tolerance the Franks and Byzantines cooperated in fully redecorating the interior (1165-69).
A Greek inscription in the north transept records this event.