The museum, housed in the southern wing of the historic Episcopal Palace (Palazzo Vescovile), is home to artefacts from the churches of the city which have been collected since the late 19th century.
Its displays of paintings, hangings and gold jewellery contain some that have considerable and undisputed importance. These artefacts demonstrate the important role played by the diocese of Velletri, with its rich historical tradition, important territorial position and leading role as patrons of the arts, all factors which encouraged artistic production.
The small archaeological section on the ground floor serves as an introduction to the five rooms upstairs, which open with a interesting Crucifixion from the workshop of Antoniazzo Romano, from the Church of the Crocifisso (the Church of the Crucifix). This can be found in the first room where works from the period between the 12th and 16th centuries are on display, among them the Veliterna Cross, a precious artefact of 12th century Palermo goldsmiths.
The second room contains works dating from the 17th to the 20th centuries, including the reliquary bust of St. Clement, a precious sculpture of Giuliano Finelli, a student and assistant of Bernini, and many liturgical objects and sacred paraments.
The third and fourth rooms contain panel paintings arranged in chronological order: among them the Madonna and Child by Gentile da Fabriano, who came to Velletri in 1633 from the Roman church of Saints Cosma and Damian, two Madonnas by Antoniazzo Romano, from different periods, and a rare painting by Giovan Battista Rositi from 1500, representing the transport of the Holy House of Loreto.
The last room contains paintings on canvas from the 17th and 19th centuries, including the Madonna of the Rosary by Sebastiano Conca, 1741, and portrait of Cardinal Ginette, a notable historical figure from Velletri, from the 19th century.