ROME — To observe the Jubilee Year of Mercy and to connect it with past jubilee years, the pilgrimage office of the Diocese of Rome is displaying historical documents proclaiming the jubilees dating back to 1300.

“Holy Pilgrimage: The Jubilee Bulls From the Vatican Secret Archives” is an exhibition of the Opera Romana Pellegrinaggi, which displays papal bulls of indiction of the jubilee years from 1300 to 2000.

The bulls are normally not available to public view and are restricted to scholars and conservationists who work with the Vatican Secret Archives, the historical archives of the papacy.

The exhibition also features bulls from the archives of the Chapter of St. Peter kept in the Vatican Library, as well as incunabula — books printed before the year 1500 — stored at the Biblioteca Casanatense.

Beginning today, the exhibition is on display daily through July 31, from 10am to 9pm, at the Palazzo del Vicariato Vechio on the Via della Pigna, a two-minute walk south of Santa Maria sopra Minerva. Each bull is accompanied by explanatory texts in English and Italian, which provide historical context for the jubilees.

Papal bulls are a kind of letter, named for the lead seal, or bulla, which were appended to the letters to verify their authenticity.

Jubilee years were historically established by papal bulls. The practice of jubilees has biblical roots, as the Mosaic era established jubilee years to be held every 50 years for the freeing of slaves and forgiveness of debts as manifestations of God’s mercy.

The practice was formally re-established in 1300 by Boniface VIII. Pilgrims to Rome were granted a plenary indulgence, under the usual conditions. Between 1300 and 2000, 29 jubilee years were held in Rome.

Pope Francis opened the Jubilee of Mercy, an extraordinary holy year, on Dec. 8, the Solemnity of the Immaculate Conception, last year. It will close Nov. 20, with the Solemnity of Christ the King.

The jubilee was officially inaugurated by the Pope when he opened the holy door in St. Peter’s Basilica. Pilgrims who pass through the door — which is only opened during jubilee years, ordinarily every 25 years or when a Pope calls for an extraordinary jubilee — can receive a plenary indulgence under the usual conditions.

The Jubilee was officially inaugurated when Pope Francis opened the Holy Door in St. Peter’s Basilica. Pilgrims who pass through the door – which is only opened during Jubilee years – can receive a plenary indulgence under the usual conditions.