Pope Benedict XVI, who is 85, surprised the world Monday morning by announcing he will resign "due to an advanced age."
• Many news organizations have reported that Pope Gregory XII was the last leader of the Roman Catholic Church to resign, in 1415. However, in this clip NBC Vatican analyst George Weigel says it's been "717 years" since the last pope abdicated, by which he probably means Celestine V, who resigned 719 years ago, in 1294. Gregory was not the pope for whom was named the Gregorian calendar (that was Gregory XIII) or Gregorian chant (Gregory the Great or Gregory II, opinions differ). XII resigned so the church could unite under a single pope after a schism. He died in 1417. Here's some background on papal resignations.