The papal throne had been vacant for 27 months when the cardinals finally elected Pietro del Morrone.

He was a hermit with a reputation for helping the poor and healing the sick, and he lived in a tiny grotto on a hillside.

The cardinals who chose him were impressed by his image as a holy man. Pietro protested that he did not want the job, but was persuaded to accept the papacy.

It was a big mistake. His lack of education led to chaos, and after just five months he decided to abdicate. He was kept a virtual prisoner until his death.

Although others have been forced from office, Celestine was the last pope to resign voluntarily, assuring him a place in Vatican history.