In France, more than 250 churches have Treasuries that can be visited. The criteria for placing objects in a Treasury have not varied much over the centuries, even though the reasons for keeping the objects have changed. The prime reason is conserving religious objects and protecting their sacred nature.
All objects in contact with the body of Christ in the form of the consecrated host and wine have a sacred nature and therefore were, until recently, made of, or at least covered with, precious materials. This category of object includes chalices that receive the precious blood, ciboria that hold the consecrated host, pyxes that are used for carrying the host, monstrances used to present the host for adoration.
Many other objects are used to celebrate mass: cruets and cruet trays, ewers and basins, or for administering sacraments: chrismatories (or chrismaria) used to hold Chrism used in baptisms and ordinations and oil for anointing of the sick were made of precious metals using highly sophisticated design.
The Treasuries also hold bishops’ attributes: mitres,
crooks and rings along with procession crosses and crucifixes.
Liturgical vestments: albs, chasubles, dalmatics, copes, stoles, and
historical illuminated books that could not withstand exposure to light and
require careful attention.
Nearby, there are objects used to celebrate the religion, and
many of them hold reliquaries. In various forms:
crosses, shrines, medallions, monstrances, pyxes, statuettes, busts etc. They contain the remains of saints the Church honours with particular devotion. Notre-Dame de Paris has the relics of many saints, but its holiest possession are the Holy Relics of the Passion of the Christ acquired by Saint Louis and kept at Sainte Chapelle until the Revolution.