This is one of the oldest and most interesting Umbrian churches. It stands on the site of Vicus ad Martis Tudertium, a way station on the old Via Flaminia. It has been the subject of annual excavation since 2008.
The church seems to have been adapted from a late imperial building, whose remains are still visible in the right wall and in the presbytery. Recent studies suggest that the present building, which incorporates these earlier walls, was built in the 7th or 8th century.
The church, which is named for the swamp in which it was built, was often flooded and fell into disrepair. A community of Benedictines reclaimed it in the 10th century and built the adjacent monastery. The Emperor Henry V confirmed the transfer of the monastery from Count Rapizzone to the Abbazia di Farfa in 1118.
Exterior
The plain rectangular façade (14th or 15th century) leans sharply forwards. The portal is made of alternate red and white ashlars with a marble cornice, and there is a beautiful rose window above.
A Roman funerary urn with relief of the sacrifice of Iphigenia is embedded in the external monastery wall.
Interior
A number of Roman cinerary urns, inscriptions and decorative reliefs are preserved inside the church.
A cippus with the inscription “Vicani Vici Martis” forms the base of the high altar.
Fragments of an old mosaic floor and of an area of pavement in opus spicatum were found during a recent restoration.
SS Antony Abbot, Peter, Fortunatus and Onuphrius (14th century)
This fresco is on the back wall.
Madonna and Child with SS Felix and Benedict (14th or 15th century)
This panel is on the back wall of the apse. The figures of SS Felix and Benedict were later additions to the original composition.
Madonna and Child with SS Barbara and Antony Abbot (15th century)
This fresco above the altar at the end of the right aisle is attributed to Nicolò di Vannuccio.