The tradition that the Baptistery was once a Roman temple is understandable when we enter the building. In general arrangement, this vast, domed space recalls the Pantheon, and in fact is enriched with elements taken from ancient monuments: monolithic columns, two sculptured sarcophagi, and part of the marble wall-sheathing. By contrast, the pavements evoke the Islamic world; in the "carpets" between the Gates of Paradise and the hall's center, oriental zodiac motifs are clearly visible. The geometric wall decoration combines late-Imperial patterns with others, of distant Germanic parentage. And the sumptuous mosaics of the dome suggest the influence of Byzantine art in central Italy. The overall effect is that of a magnificent crossroads of the several cultures of medieval Europe.


The old baptismal font, with its octagonal enclosing wall, stood at the center of this interior space (the outlines are traced in the pavement). Looking up from the font toward the dome, believers saw a huge Christ in the l3th-century mosaics, and -under Christ's feet -the dead rising from their sepulchers. These figures represent the Last Judgement, when the Risen Lord will summon living and dead alike to account for their actions. To Christ's right (the viewer's left) are the souls of the righteous "in the bosom" of Abraham, Isaac and Jacob, the Patriarchs of ancient Israel; to his left (the viewer's right) is Hell. These images of death and resurrection have singular impact due to the presence of tombs inside and, formerly, outside the Baptistery, and suggest the deepest meaning of Christian Baptism. "When we were baptised in Christ Jesus ... we went into the tomb with him and joined him in death, so that as Christ was raised from the dead by the Father's glory, we too might have a new life", as Saint Paul explains (Letter to the Romans, 6, 3-4).


Plan of the mosaics in the Baptistery dome.

1 Last Judgement

2 Choirs of Angels

3 Stories from the Book of Genesis

4 Stories of Joseph

5 Stories of Mary and Christ

6 Stories of Saint John the Baptist

 

In the remaining five sectors of the dome, horizontal tiers of mosaic decoration tell the stories of Saint John the Baptist, Christ, the Patriarch Joseph, and the beginnings of human life (Adam and Eve, Cain and Abel, Noah and his family). Gazing up at these biblical personages, the faithful could see themselves as members of God's people and part of the history of salvation: could say, with the author of Hebrews 12,1, "with so many witnesses in a great cloud on every side of us, we too then ... keep running steadily in the race we have started, our gaze fixed on Jesus" who is visible in the mosaics above the altar.
In the uppermost tier, nearest the light, we see the choirs of angels.