WHAT HAPPENED TO POPES WHO REIGNED IN THE PAST: ONE WAS IMPRISONED FOR RESIGNING, ANOTHER WAS...

He is the first Pope to resign after 598 years, Pope Benedict XVI's resignation made us unruffle history. Out of the 65 Popes known in history, he's one of the few who resigned. 

Pope benedict says he's stepping down on health grounds, but past Pope's resigned for other reasons.

The last pope to resign before him, Gregory XII, did so in 1415, 10 years into his tenure, in the midst of a leadership crisis in the church known as the Great Western Schism. Three rival popes had been selected by separate factions of the church, and a group of bishops called the Council of Constance was trying to heal the schism. In an interview with Vatican Radio, Donald S. Prudlo, a papal historian at Jacksonville State University in Jacksonville, Ala., said Gregory XII had offered to resign so that the council could choose a new pope whom all factions would recognize. It took two years after Gregory XII’s departure to elect his successor, Martin V.

Other popes known to have resigned:

Pope Celestine V: A recluse who only reluctantly accepted his election in 1294, Celestine V resigned and fled the Vatican after just three months to wander in the mountains. According to a history timeline on Christianity.com, the bishop who became his successor, Boniface VIII, was intent on ensuring that Celestine V did not become an example for future popes, and ordered Celestine V seized and imprisoned as he was about to sail to Greece. He died in custody in 1296 at the age of 81, and was declared a saint in 1313.

Benedict IX: One of the youngest popes, he was elected at the age of about 20 in 1032, and became notorious for licentious behavior and for selling the papacy to his godfather, Gregory VI, in 1045, and then twice reclaiming the position.

Gregory VI: Considered a man of great reputation, Gregory VI had thought Benedict IX unworthy of the papacy, and essentially bribed him to resign. He was recognized as pope in Benedict’s stead, but when Benedict’s attempt at marriage failed and he wanted to return to the papacy, a power struggle ensued. A council of bishops called upon Gregory VI to resign after less than two years in office because he had obtained the papacy through bribery.

By contrast, the resignation of Benedict XVI after an eight-year tenure will essentially be a retirement at the age of 85, after the pope showed increasingly public signs of fatigue in recent months. His last day as pope will be Feb. 28, coincidentally the feast day of a revered fifth-century pope, Saint Hilarius.