Detail of dedicatory mosaic. The lengthy Latin text, written in gold on a blue background, is flanked by two female figures who personify the Church of the Jews and the Church of the Gentiles. The inscription translates as follows:
"When Celestinus held the highest apostolic throne and shone forth gloriously as the foremost bishop of the whole world, a presbyter of the city, Illyrian by brith, named Peter and worthy of that great name, established this building at which you look in wonder. From his earliest years he was brought up in the hall of Christ - rich to the poor, poor to himself, one who shunned the good things of life on earth and deserved to hope for the life to come."
This inscription is important not only because it gives the founder's name and date of the church, but also because it expresses the doctrine of papal supremacy, which was still developing at that time.