Inside the cemetary of Ardea, the Church of St. Marina nestles against the sandstone rock known as della Civitavecchia. An inscription over the entrance establishes that the building was built in 1191 by Cencio Savelli, the future Pope Honorius III.
The construction was preceded by a small porch, which is now only ruins and traces of pictorial decoration. The lintels of the entrance door are supported by two lions and the architrave is decorated with the representation of three monks, the central one being St. Marina.
The interior features a single nave and three pairs of columns which support the pitched roof. There is a cell dug out of the sandstone, accessible from behind the altar. This is a rectangular space with apses in the walls, probably a pagan nympheum from the 2nd century which was later used as a crypt or chapel in the 12th century.
According to legend, St. Marina lived like a monk and was willing to be unjustly accused to keep her true sex a secret as promised to her father on his death bed. She was later thrown out of the monastery and found refuge in a cave where she lived as a hermit. There is a 17th century fresco of the saint in the central niche.