This ancient church, the oldest and most important Christian monument in the Roman Forum, is a unique treasure trove of early Christian art. Its cavernous interior is lined with exquisite 6th- to 9th-century frescoes. At the time of research it was closed to the public, but it is occasionally opened for temporary exhibitions. And if it's open, it's a must-see.
Particularly impressive is an image on the east wall showing Christ with the fathers of the Eastern and Western churches and a hanging depiction of the Virgin Mary with child, one of the earliest icons in existence.
The church, which was originally built inside a complex of Roman buildings, was buried in rubble during an earthquake in 847 and only rediscovered in 1900.