The floor of the original Constantininan church was completely paved over in mosaic. This was discovered as a result of the excavations carried out by the British government between 1932 and 1934. The fourth century pavement rose in the direction of the area of the apse, with a difference in level that varied between 75 and 31 centimeters. During the Byzantine period, due to the variations in the floor level within the church, the floor was re-done using white-veined marble. Through trapdoors opening in the pavement it is still possible to enjoy a view of the ancient mosaics. Their workmanship is truly detailed and refined, above all those in the nave. It has been calculated that the density of tesserae (small squares of stone or glass) is 20 per cm2, compared to the 10 per cm2 characteristic of ordinary mosaics. This factor by itself allows one to understand why these decorations are so highly valued, as their higher density permitted the representation of more refined images, and the reproduction of more shades of color. The result was decorative mosaics that are extremely detailed, reflecting the importance of this Holy Place. These mosaics, which cover the nave and apse, display geometrical and decorative elements (swastikas, circles and cornices with interwoven bands). More rare are themes related to plants, such as acanthus leaves and vines. Rarer still is the representation of a rooster in the north transept. The absence of living beings is consistent with the Middle Eastern tradition which did not use representations of either animals or humans. A very interesting part of the mosaic decoration is preserved in the left corner of the nave where, opening a trapdoor, one can see a monogram bearing the Greek letters ΙΧΘΥΣ. Literally meaning “fish” in Greek, this was used as an acronym and symbol in ancient times to indicate the name of Christ (“Jesus Christ, God’s Son, Savior”): this is the only element that confirms that the Holy Place was Christian. A similar use of a monogram had come to be used during the Classical period at the entrance to houses of Roman patricians, along with busts of the owners. This fact has led to the hypothesis that the monogram marked the ancient entrance to the sacred area and to the “house of Jesus”. Based on the analysis of the excavations carried out by the British, it has been hypothesized that the entry to the presbytery in the Constantinian church was by means of a staircase starting precisely from the spot where the mosaic is located. According to Father Bagatti, the stairs used to enter the presbytery were torn down in order to construct a direct entrance to the grotto.