Read the article Why the Catholic Church Celebrates Jubilee Years: Restoration, Renewal, Mercy and Freedom in the Denver Catholic.
In the face of great suffering caused by wars and diseases such as the plague, thousands of pilgrims came to Rome at Christmas in 1299. Cardinal Giacomo Gaetani Stefaneschi, the contemporary and counsellor of Pope Boniface VIII, and author of a treatise on the first Christian jubilee, noted that the proclamation of the jubilee owed its origin to the statements of certain aged pilgrims who persuaded Boniface that great indulgences had been granted to all pilgrims in Rome about a hundred years before.
On 22 February 1300, Boniface published the bull "Antiquorum habet fida relatio", in which, appealing vaguely to the precedent of past ages, he declared "...the most full, pardon of all their sins", to those who fulfill certain conditions. These are, first, that being truly penitent they confess their sins, and secondly, that they visit the basilicas of St. Peter and St. Paul in Rome, at least once a day for a specified time—in the case of the inhabitants of the city for 30 days, in the case of strangers for 15 days.