The secret -- or, more accurately, "private" -- archives were founded by Pope Paul V in 1612. Since 1881, they have been opened to scholars conducting research.

The documents in the exhibit include the "Privilegium Ottonianum," signed by Pope John XII and Emperor Otto I in 962, establishing the Papal States; the letter that members of the English Parliament wrote to Pope Clement VII in 1530 asking him to annul the marriage of King Henry VIII and Catherine of Aragon; selections of documents from 1616 to 1633 related to the trial of Galileo Galilei; a letter written on silk in 1650 from Empress Helena Wang of China to Pope Innocent X; and a letter on birch bark from the Ojibwe people of Grassy Lake, Ontario, written to Pope Leo XIII in 1887.

The exhibit also includes some fragments collected behind St. Peter's Basilica from an Allied bomb that fell nearby in 1943, and the report of a Vatican policeman who was on duty that night.

In the preface to the exhibit catalogue, Cardinal Raffaele Farina, archivist and librarian of the Holy Roman Church, said the exhibit would introduce visitors to the archives' "service to the church and to culture, carried out over four centuries with a tireless work of safekeeping, cataloging and care" using the most advanced technology available.

Bishop Sergio Pagano, prefect of the archives, told Vatican Radio that the documents in the exhibit were selected to give people an idea of the historical range of the archives' holdings, the diversity of materials preserved and the global reach of the Vatican's interests and concerns.