This is the most historic document in the collection. It was signed by Pope Pius V and dated June 20th, 1667.
The document was written to the senate of Milan asking them to give support to Cardinal Charles Borromeo, the greatest saint of the Counter Reformation. He was the Cardinal-Archbishop of Milan at the time of Pius V. He is asking the senate to give Borromeo support in the suppression of a religious order referred to as the Humiliati. They were a religious order that became very corrupt during the time of the Counter Reformation. Pius V was suppressing this order using Charles Borromeo as the main operative since the Humiliati were based in Milan.
This document has a great deal of significance because it lent strength to the suppression of this order.