The patron saints of Trivento are Saints Nazarius, Celsus and Victor, celebrated on 28 July. The town's cathedral was dedicated to them, as attested by the consecration inscription dated 15 May 1076; the building stands on an ancient altar dedicated to the goddess Diana, from some centuries before Christ. Enlarged in the 13th century and fully restored in Baroque style in 1726, the cathedral also houses the paleo-Christian crypt of San Casto, arranged in seven small naves with cross vaults, where a medieval bas-relief depicts the Trinity between two angels and two dolphins.
Near the saint's tomb — according to tradition the founder of the diocese by the will of Pope Clement I — the relic of the Holy Thorn is also kept. The episcopal see of Trivento is reliably documented from the 10th century and reached its greatest development in the 14th century, when the town became one of the most important religious centres of what is now Molise.
