Just outside the walls of the fortified castle of San Terenziano, locus petrosus (stony place) due to the abundance and prestige of travertine and limestone quarries and the quality of the labor of local stonemasons, a rare example of a 'double church'.
The church is named after two martyr saints: St Terenziano and St Flacco.
Terenziano, the first bishop of Todi, was beheaded by Emperor Adriano together with Flacco: the following night, some Christian women collected the remains of the martyrs and brought them to the Petroso plateau, which from that moment on was called S. Terenziano.
Its structure is very interesting, in fact, mainly due to its double overlying church confirmation: the lower one dates back to the first decades of the 11th century, the upper one rebuilt in the late 13th century, when the one below it was also enlarged according to a logic reminiscent of the structure of the double Basilica of St. Francis in Assisi.
The pink limestone used is locally sourced. Flacco's sarcophagus remained in its original state and can still be seen in its place in a grotto on the left wall, while Terenziano's sarcophagus was moved under the altar of the upper church.
Numerous Roman and early medieval decorative fragments have been reused all over the interior.
The interior has a single nave, with a semicircular apse, gabled roof and façade. It is a typical Romanesque construction and was rebuilt in the 13th century. On the side, walls are two late Renaissance aedicules.
Beneath the main church is the present crypt, which is accessed not internally, but by external stairs: it is the original body on which the upper one was later erected. Numerous Roman and early medieval decorative fragments are walled up almost everywhere.
The travertine sarcophagus containing the bones of St Terenziano was moved under the altar of the upper church. Flacco's sarcophagus remained in its original state and can still be seen in its place: a grotto opening in the left wall, with access from the penultimate bay towards the back, through a brick arch.
