Citing failing strength of "mind and body," Pope Benedict XVI stunned his closest aides and more than 1 billion Catholics Monday by announcing his resignation, becoming the first pope to do so in nearly 600 years and ending the tenure of a formidable theologian who preached a gospel of conservative faith to a fast-changing world.
Keeping with his reputation as a traditionalist, the pontiff delivered his resignation effective Feb. 28 in Latin to a routine meeting of cardinals.
Benedict emphasized that to carry out the duties of being pope, "both strength of mind and body are necessary — strengths which in the last few months, have deteriorated in me."
"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited" to the demands of being the pope, he told the cardinals.
"For this reason, and well-aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of bishop of Rome, successor of Saint Peter," he said.
The decision by the 85-year-old German pontiff sets up a pivotal leadership contest in the marbled halls of the Vatican that is coming sooner than observers expected.
Although questions about the pope's health have long swirled — he was occasionally filmed nodding off during mass — he seemed committed to continuing a papacy that divided Catholics and non-Catholics alike.
But the pope's brother, Georg Ratzinger, also a priest, said the pontiff had informed him of his decision "months ago."
"He has gotten tired faster and faster and walking has become hard for him," Ratzinger said. He added that his brother, who was born Joseph Aloisius Ratzinger and ordained a priest in the aftermath of World War II, did "the best he possibly could have done" in his role.
The conclave to choose the next pope is expected to convene in mid-March, with a new pope in place for Easter.
Although Benedict will not vote, he has hand-picked the bulk of the College of Cardinals — the princes of the church who will elect his successor — to guarantee his conservative legacy and ensure an orthodox future for the church.
The resignation may mean that age will become less of a factor when electing a new pope, since candidates may no longer feel compelled to stay for life.
"For the century to come, I think that none of Benedict's successors will feel morally obliged to remain until their death," said Paris Cardinal Andre Vingt-Trois.
The Vatican said Benedict would live in a congregation for cloistered nuns inside the Vatican, although he will be free to go in and out. Much of this is unchartered territory. The Vatican's chief spokesman, the Rev. Federico Lombardi, said he isn't even sure of Benedict's title — perhaps "pope emeritus."
Since becoming pope in 2005, Benedict has charted a very conservative course for the church, trying to reawaken Christianity in Europe where it had fallen by the wayside.
He tried to return the church to its traditional roots, which he felt had been betrayed by a botched interpretation of the modernizing reforms of the Second Vatican Council.
His efforts though, were overshadowed by a worldwide clerical sex abuse scandal, communication gaffes that outraged Jews and Muslims alike and, more recently, a scandal over leaked documents by his own butler.
There are several papal contenders in the wings, but no obvious front-runner — the same situation as when Benedict was elected after the death of John Paul.
As in recent elections, some push is expected for the election of a Third World pope, with several names emerging from Asia, Africa and Latin America, home to about 40 percent of the world's Catholics.
Perhaps the greatest challenge of his papacy has emerged in the spread of clerical sex abuse scandals from the United States into other places including Ireland and Germany, where the pope was born and served as archbishop.
He encouraged a revival of the Latin Mass and promoted traditionalists in the Vatican hierarchy, determined to amplify the church's message of morality and the role of Roman Catholicism as the one true faith.
He sought to win back conservative Catholics opposed to the Second Vatican Council of 1962, and attempted to recruit new members, including Anglicans disenchanted with liberal views on female as well as openly gay clergy in their denomination.
Liberal Catholics have bemoaned his promotion of a generation of conservative bishops who believe the church will hold together best if its teachings are communicated as black and white.
A symbol to them has been the crackdown on the largest group of U.S. nuns who the Vatican said were straying too far in their writings and lectures about homosexuality and contraception.
Traditional Catholics, however, celebrated his focus on orthodoxy.
"If you don't sell full-throttle Catholicism, people are not going to buy it," said George Weigel, who has written multiple books about the church and the pope. "Everyone knows the whole package is more compelling and interesting than some sort of Catholic hors d'oeuvres that leave you hungry."
The Vatican newspaper, L'Osservatore Romano, said Benedict decided to resign after his March 2012 trip to Mexico and Cuba, an exhausting but exhilarating visit where he met with fellow-octogenarian Fidel Castro and was treated to a raucous and warm welcome.
It stressed that no specific medical condition prompted Benedict's decision, saying he remains fully lucid and took his decision independently.
Although popes are allowed to resign, only a handful has done it — and none for a very long time.
The last pope to resign was Pope Gregory XII, who stepped down in 1415 in a deal to end the Great Western Schism, a dispute among competing papal claimants. The most famous resignation was Pope Celestine V in 1294; Dante placed him in hell for it.
On Monday, Benedict said he plans to serve the church for the remainder of his days "through a life dedicated to prayer." The Vatican said after he resigns he will travel to Castel Gandolfo, the papal summer retreat, and then live in the monastery.
Contenders to be Benedict's successor include Cardinal Angelo Scola, archbishop of Milan; Cardinal Christoph Schoenborn, a protege and former theology student of Benedict's; and Cardinal Marc Ouellet, the Canadian head of the Vatican's office for bishops.
Only four popes have resigned. Benedict is the first pontiff to step down since Pope Gregory XII, who quit in 1415 in a deal to end the Great Western Schism.
Cardinals meet in mid-March in the Sistine Chapel to elect a pope. Ballots are burned after each round of voting. White smoke from the chimney means a pope has been elected.
Benedict said he plans to serve the church for the remainder of his days "through a life dedicated to prayer." Church officials said he will live in a monastery inside the Vatican.