The word, bull comes from the Latin, bubble. It is the lead seal that is appended to the end of a document acting as the signature of the pope. On one side, it contains the pope’s name and on the other, images of Saints Peter and Paul from whom he is given his authority.
The bull is generally an official document of the Holy Father. We know by the choice of threading used, either silk or twine, the importance of any particular bull.
This bulla is extremely rare as it was used during the reign of Pope Paschal II who reigned from 1099-1118.
It is the oldest artifact in the Collection.
Here is a link to Papal History/Paschal II