Grotto of the Nativity is precisely the place where tradition says that Jesus was born. The Basilica of the Nativity of Bethlehem, Palestine, contains below the altar the Grotto of the Nativity.
The entrance today is placed sideways with respect to the location where Jesus was born, but it is thought that in the fourth century the entrance was located behind the presbytery. The small façades of the two side entrances date back to the times of the Crusaders.
The Grotto is entered by descending the stairs to the right of the iconostasis. Here the space is very narrow and restricted and the walls, which were originally irregular, form an almost-rectangular perimeter.
The natural walls of the cave, decorated in the Constantine period, were covered with marble during the Byzantine period.
The Altar of the Nativity only began to be venerated in the Byzantine period when this space was created to commemorate the precise place in which Jesus had been born.