When Boniface introduced the idea in this form, he intended for Jubilees to happen every 100 years, but in 1343, Pope Clement VI shortened the interval to 50 years. Their popularity was such that Urban VI declared 40 years later that every 33 years was an appropriate way to remember the life of Christ and made 1390 a Jubilee as well. Enough people flocked to Rome in 1400 that an unofficial Holy Year took place then too. Finally, people settled on 25 years as the appropriate interval.
The declaration of a Jubilee produced more than just spiritual benefits. The great numbers of pilgrims crowding to Rome brought economic prosperity to the city and to those towns on the way there as well. Charitable institutions, particularly religious ones, received large donations.
However, the large numbers had the potential to create problems too, some more serious than others. As space ran out in inns and hospitals, some pilgrims found themselves without somewhere to sleep until householders began offering space in their homes. More pressing was the danger presented by large numbers of people in small places. A spooked donkey or simply a few individuals suddenly inspired to religious fervor could cause a crush of people, leading to a number of deaths and serious injuries, as happened in St. Peter’s in 1300 and on the Ponte Sant’ Angelo in 1450.
Jubilees have continued to occur every 50 years up to the present day, with the most recent in 2000. While ordinarily the next one would not occur ‘til 2050, the current pope, Francis, has declared a special Jubilee from December 2015 to November 2016, the Year of Mercy.
*He pulled the idea from Leviticus and the Jewish idea of a Jubilee Year. Jews, however, no longer celebrate Jubilees as they are only observed when the twelve tribes all reside in Israel.
**This would not gain them absolution. It simply meant they did not have to perform the penance imposed.