Pope Gregory XII - who reigned from 1406 to 1415 - did so to end what was called the Western Schism.

BBC: How does a Pope resign from office?

But resignation is extremely rare: the last pontiff to step aside was Pope Gregory XII, who resigned in 1415 amid a schism within the Church.

BBC: Pope Benedict has a pacemaker, the Vatican confirms

ROME Whatever challenges the Roman Catholic Church faces in 2013, they pale compare to those that prompted the resignation 598 years ago of Pope Gregory XII.

WSJ: When Last Pope Retired, Church Was in Turmoil