Towards the end of the fifth century it was certainly a bishopric, since Valerius, Bishop of Calenum, was present at the Roman Council held by Pope Symmachus in 499.

[3] In the first six centuries, only eight names have been recorded, and these only in a list of bishops found in the Breviarium et Martyrologium of the Church of Calvi, a devotional and hagiographic work.

The cathedral of Calvi, dedicated to the taking up of the body of the Virgin Mary into heaven, is administered and served by a corporation called the Chapter, composed of twelve Canons, headed by the Primicerius.

[7] The seminary of Calvi was founded by Bishop Giuseppe del Pozzo (1718–1724), and was blessed by Pope Benedict XIII as he was returning to Rome from Benevento in 1727.

[11] In 1575, the new bishop, Giovanni Paolo Marincola (1575–1588), held a diocesan synod, and ordered the construction of a seminary, in accordance with the decrees of the Council of Trent.

Pope John Paul II issued a decree, "Quamquam Ecclesia," on 30 April 1979, ordering the changes.

The dioceses formerly members of the suppressed Province of Capua (Gaeta, Calvi and Teano, Caserta, and Sessa Arunca) became suffragans of Naples.

[17] On 18 February 1984, the Vatican and the Italian State signed a new and revised concordat, which was accompanied in the next year by enabling legislation.

According to the agreement, the practice of having one bishop govern two separate dioceses at the same time, aeque personaliter, was abolished.