Crossing vault (detail of the south cell)

Either writing or absorbed in scripture, the evangelists occupy one half of each triangular field; a table writing desk is in the middle; and a view of a city is in the other half. In the pinnacle of each vault cell is a patch of cloud from which an angel descends and, as a visual sign of divine inspiration, touches the ear of the evangelist. The cities depicted represent, or once represented, the parts of the world to which each evangelist directed his message: YTALIA, ACCHAIA, ASIA, IUDEA.

The view of Rome opposite the evangelist Mark features prominent buildings in the city - e.g., the Castel Sant’Angelo, the Meta Romuili, Old St Peter’s, the Pantheon, the Capitol with the Palazzo dei Senatori, the Torre delle Milizie, and apparently the church of Santi Apostoli - with a fidelity that was unusual for the time.