Tradition dictates that each Jubilee is proclaimed through the publication of a Papal (or Pontifical) ‘Bull of Indiction’. By ‘Bull’ is meant an official document, generally written in Latin, bearing the seal of the Pope, the shape of which gives its name to the document itself.
In the past the seal was usually made of lead and bore, on the front, the image of the Holy Apostles Peter and Paul, founders of the Church of Rome, and, on the back, the name of the current Pontiff. Later an ink stamp replaced the metal seal, which, however, continued to be used for more important documents.
Each Bull is identified by its initial words. For example, Saint John Paul II proclaimed the Great Jubilee of the Year 2000 with the Bull Incarnationis Mysterium (The Mystery of the Incarnation), while Pope Francis proclaimed the Extraordinary Jubilee of Mercy (2015-2016) with the Bull Misericordiae vultus (The face of mercy).
The Bull announcing the Jubilee, which indicates the dates of the beginning and end of the Holy Year, is usually issued the previous year, coinciding with the Solemnity of the Ascension. For the 2025 Jubilee, publication is expected on May 9, 2024.