One of the most remarkable churches in the city. The complex contains two churches, one above the other, where the 10th-century Romanesque style impressively blends with the 11th-century Gothic style.

The lower church was built during the 11th–12th centuries on the remains of an earlier church and was dedicated to Saints Fermo and Rustico (Fermo e Rustico), who were executed at this site. In the 14th century, the upper church was established by the Franciscan order, introducing the Gothic style to the building, and over the years they also added frescoes, small spires, and other symbols.

The church façade clearly reflects this combination: the lower part features a Romanesque entrance, while the upper part alternates tuff and terracotta stones, includes four Gothic windows, and has prominent spires that visually extend the church upward. The entrance door bears 24 panels depicting the story of the two saints.

Inside, the church has a magnificent wooden ceiling, five longitudinal naves, and side chapels. Among the ancient paintings and sculptures on the right side, there is access to the lower church and the Romanesque cloister.