Too tired to go on, Pope Benedict resigns

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Rome (CNN) -- The spiritual leader of 1.2 billion Roman Catholics, Pope Benedict XVI, surprised the world Monday by saying he will resign at the end of the month "because of advanced age."

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 the Catholic world and led to frenzied speculation about who would replace him, including a debate about the merits of naming a pontiff from the developing world, where the church continues to grow, versus one from Europe, where it has deep historical roots.

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But that decision will not be made by Benedict, who will leave his post at 8 p.m. on February 28, said the Rev. Federico Lombardi, a Vatican spokesman.

"Before Easter, we will have the new pope," he said.

While Benedict won't be directly involved in his successor's selection, his influence will undoubtedly be felt. He appointed 67 of the 117 cardinals that -- as of Monday -- are set to make the decision.

The number of electors could drop to 115, as two cardinals will turn 80 in March, when their age makes them ineligible to cast a vote. More than two thirds of whatever the final number must agree on the next pope, a decision that will be announced to the world in the form a puff of white smoke emerging from a chimney in the Vatican.

CNN Senior Vatican Analyst John Allen said that means the next pope, no matter where he is from, will probably continue in Benedict's conservative tradition, which has seen the church take a firm line on issues such as abortion, birth control and divorce.