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The Basilica of St. Paul Outside the Walls. The mosaic of the triumphal arch, also called “of Galla Placidia.” At the center is Christ Pantocrator and on either side are the symbols of the four Evangelists. Below them are 24 old men, and under them, on a blue background, are St. Paul and St. Peter.

© Zvonimir Atletic | Shutterstock