Pope Ratzinger suddenly quits
The first pope to quit in 600 years. What's really going on here?
Too tired to go on, Pope Benedict resigns - CNN.com

It's the first time a pope has stepped down in nearly 600 years.
"Strength of mind and body are necessary, strength which in the last few months has deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me," said Benedict, 85, according to the Vatican.
The news startled and shocked the Catholic world and led to frenzied speculation about who would replace him.
. . .
Benedict will become the first pope to resign since Gregory XII in 1415. In that case, Gregory quit to end a civil war within the church in which more than one man claimed to be pope.