The patron San Sisto has two days of festivities: January 11 and the Wednesday after Easter. St. Sixtus I was the 7th bishop of Rome and pope under the Emperor Hadrian, from 117-126, but other historians give other time intervals. During his papacy the first disagreements arose between the Church of Rome and the Eastern churches on the feast of Passover, which at that time was celebrated only in the East. According to a legend, Pope Sixtus I sent the first missionary, Bishop Pilgrim, to evangelize Gaul.

The history of the relationship between Alatri and San Sisto is very interesting because it seems likely that the Saint had agreed to become the patron of Alatri and to protect it. It is said that in 1132 the Count of Alife, Rainolf, requested to the Pope Anacleto II to have a relic of some saint to help him free his city from a terrible plague. The pope granted an urn containing the relics of St. Sixtus and the urn was loaded on the back of a mule.

In their journey back to Alife the mule refused in any way to obey the orders of commanders and headed to Alatri where he arrived knelt in front of the church of San Matteo and than at the Acropolis in front of the cathedral. The mule waited for Bishop Crescenzio who took the urn containing the relics of the saint and since that day, 11 January 1132, Alatri was freed from the plague. To give thanks for the miracle citizens of Alatri donated to the inhabitants of Alife a finger as a relic of the saint. For this reason, on January 11 we celebrate the saint.

The Wednesday after Easter holiday, on which a solemn procession takes place through the streets of Alatri, is due instead to another miracle. In 1186 Alatri was besieged by the troops of Henry VI, son of Frederick Barbarossa, and after nine days of resistance the Alatri residents went exhausted in front of their Patron Saint Sixtus to invoke help and protection.

The inhabitants felt reinforced and managed to defeat the enemy just on the Wednesday after Easter and, from that day, it was declared a festive day dedicated to their patron saint.

The statue of the saint is covered with gold wood with the head, arm and palm in silver. Its weight is about 7 tons and is carried in procession through the streets of the city on the shoulders by 20/25 members of the Brotherhood.