Latin inscriptions are present on the exterior of the reliquary; they tell us to whom these relics belonged.

We can read: "IN HOC VASE HABETUR COSTA PETRI APOSTOLI", which can be translated as: "In this vessel lies the rib of the Apostle Peter."

Saint Peter, considered the patron and founding father of the Roman Catholic Church, is one of the twelve apostles entrusted with spreading Christianity.

The provenance of this relic remains unknown. Several hypotheses can be considered: it may have been a gift made in honor of Jacques de Vitry or acquisitions obtained during his journey to the Middle East, as is the case for other relics preserved in the reliquary and attested by authentic documents. In any case, it is the relic of Saint Peter that prevailed among all these relics in determining its shape.