The town's main church, Santa Maria Assunta, dates to at least the 11th century.
Many ancient stones carved with pagan and early Christian iconographs dating to the 7th and 8th centuries were incorporated into the present structure.
 It was likely that these stones were part of a pagan temple that originally sat on the same site.
It is unclear if the present structure was standing at the time of Pope Leo IX’s visit in 1053, but the diocese records clearly show that the designation of Santa Maria dell'Assunta was elevated to a cathedral in 1061 and was presided over a Bishop by the name of Peter.

On April 7, 1751 relics of Saint Gaudentius (San Gaudenzio) were transported by two Capuchin friars from the catacombs of St. Priscilla to the Cathedral in Guardialfiera.
These were given to Mons.
Pasquale Zaini, the Bishop of Guardialfiera, by Pope Benedict XIV.
The relics can still be seen today in Santa Maria dell'Assunta and are paraded through the town on the feast of San Gaudenzio (1 and 2 June).
It remains unclear who exactly Saint Gaudentius was, although from historical texts he is referred to as a martyr.
It has been alternatively claimed that he was either the architect who designed the Flavian Amphitheater in Rome (also known as the "Colosseum"), or Saint Gaudentius of Rimini.

After an earthquake in 1456, the cathedral was rebuilt and in 1460 a Holy Door (Porta Santa) was added to the north-east facing wall of the cathedral by Bishop Jacopo.
This is one of the few Holy Doors outside of Rome and is opened once every year during the feast of San Gaudenzio except during Jubilee Years when the Holy Doors in Rome are opened.

In 1975 a medieval crypt was discovered during the restoration of the cathedral.
The town's main church, Santa Maria Assunta, dates to at least the 11th century. Many ancient stones carved with pagan and early Christian iconographs dating to the 7th and 8th centuries were incorporated into the present structure.  It was likely that these stones were part of a pagan temple that originally sat on the same site. It is unclear if the present structure was standing at the time of Pope Leo IX’s visit in 1053, but the diocese records clearly show that the designation of Santa Maria dell'Assunta was elevated to a cathedral in 1061 and was presided over a Bishop by the name of Peter.
On April 7, 1751 relics of Saint Gaudentius (San Gaudenzio) were transported by two Capuchin friars from the catacombs of St. Priscilla to the Cathedral in Guardialfiera. These were given to Mons. Pasquale Zaini, the Bishop of Guardialfiera, by Pope Benedict XIV. The relics can still be seen today in Santa Maria dell'Assunta and are paraded through the town on the feast of San Gaudenzio (1 and 2 June). It remains unclear who exactly Saint Gaudentius was, although from historical texts he is referred to as a martyr. It has been alternatively claimed that he was either the architect who designed the Flavian Amphitheater in Rome (also known as the "Colosseum"), or Saint Gaudentius of Rimini.
After an earthquake in 1456, the cathedral was rebuilt and in 1460 a Holy Door (Porta Santa) was added to the north-east facing wall of the cathedral by Bishop Jacopo. This is one of the few Holy Doors outside of Rome and is opened once every year during the feast of San Gaudenzio except during Jubilee Years when the Holy Doors in Rome are opened.
In 1975 a medieval crypt was discovered during the restoration of the cathedral.
Guardialfiera