The cathedral of Ferentino was built in Romanesque style during the episcopacy of Bishop Augustine at the beginning of the 12th century. It is dedicated to the Roman martyr brothers John and Paul. It was built using the remains of previous pagan temples and buildings, built on the esplanade of the acropolis.

The front of the church is sober; the central door and the doors on right and on left are decorated with lunettes. In the early 1900s the painter Eugenio Cisterna frescoed the three lunettes of the portals with new decorations: the painting of the lunette over the main portal depicts the Madonna and child between Saints John and Paul; the painting of the lunette on the right door represents St. Ambrose with his white horse; the painting of the lunette on the left door represents St. Peter, in memory of the church dedicated to him and destroyed in the middle-nineteenth for a new cathedral never built.

The interior of the church is made beautiful from the mosaics that the Cosmati have realized in the thirteenth century. The floor was the work of Paul. The high altar, which is accessed by five steps, is adorned by the ciborium of the Roman marble worker DRUDO DE TRIVIO (in the first half of the 13th century).

On the walls, on triumphant arch and on arch apse there are frescoes, decorative painting by Eugenio Cisterna in 1904. Very interesting fresco of the triumphal arch which depicts the Annunciation of Mary; such as the fresco of the arch ap hich depicts Christ Pantocrator in Majesty.