Let us stop now on a treasure both of art and faith, the most precious of the Basilica: the mosaic floor. It is the widest and oldest floor in the Christian western world, it is a magnificient example of Constantinian Art. 
The mosaic is made up of ten carpets separated by strips with "girali" (wreaths) of shoots and leaves of Acanthus. The biggest carpet, which covered the presbytery is the western one. 
It can be defined as a catechism through images, as each image has relevance, liveliness, imagination and the truth of faith, those truths which, in the year 313, could finally be, freely and openly, proclamed to everyone in public with joy and with no more fear of persecution