The Diocesan Museum is not very big but it has some rarities.
First of all are the medieval avory altar pieces. Well, nobody knows, sincerely, what it is and even how the pieces of this puzzle were composed originally. But the 69 pieces work that represents scenes from New and Old Testament is the only so complete collection in the world.
The second rarity are the pages of the Exultet -a "book" of images used to show to the believers what is the priest telling during the Mass. The persons did not understand latin and they used these pictures to make them participate consciously.
The next interesting object exposed in the diocesan Museum is the cross of Robert Guiscard. I'm not very sure that this cross is effectively the property of Robert Guiscard, the Normann Conquirer of Salerno but the artifact is very special in any case.