Tiara of Pope Gregory XIII
The Tiara of Pope Gregory XIII is the oldest surviving papal tiara in existence. Its actual date of manufacture is not recorded. It is known, however, that it was manufactured during the reign of Pope Gregory XIII (1572-1585), the creator of the Gregorian calendar.
Until 1798 many ancient tiaras existed in the Vatican, but invading French troops stole and smashed all the tiaras they could get their hands on, stealing their jewels, which they transported back to Paris. It is unknown how Gregory XIII's tiara survived the destruction.
Though it is the oldest papal tiara, there are no modern recorded cases of it being worn by popes, many of whom used the 1834 tiara of Pope Gregory XVI, the Palatine Tiara, or a tiara donated to them on their election.
The Tiara of Gregory XIII continues to be used to crown a statue of Saint Peter in St. Peter's Basilica on the saint's feast day every year.