The Diocesan museum and of the Codex was the first diocesan museum founded in Calabria in 1952.

On 3rd July 2016 a brand new museum has been opened divided in two sections: one entirely dedicated to the Codex Purpureus while the other is dedicated to the history of the Diocese and of the city of Rossano through centuries with an interesting exhibition of different art-works of various periods and types, divided into chronological and thematic areas. Both sections are enriched by the presence of touch-screen devices that allow further knowledge of the Codex and the other masterpieces.

The Codex Purpureus is without any doubt the most important and representative jewel of the museum, it is a Greek-byzantine manuscript of the VI century , made of 188 pages and written on purple-dyed vellum. It contains the gospels of Matthew and Mark and a series of 15 superb illuminations .On 9th October 2015, the Codex has been recognized as world heritage and inscribed in the section "Memory of the World" by the UNESCO.

The art collection of the museum is furthermore enriched by the presence of a Greek-mirror in bronze, dating V century B.C., an imposing silver bust depicting the Achiropita, the Our Lady well venerated in the city of Rossano; a post-Byzantine icon depicting the Pietà, made in 1499 by the Cretan artist Andrea Pavias, a precious miniature of parchment called The mystical marriage of Saint Catherine, painted by a tuscan-roman painter between XVI and XVII century, a silver monstrance called Greek sphere , numerous liturgical objects and musical codices.