VATICAN CITY — With a few words in Latin, Pope Benedict XVI did what no pope has done in more than half a millennium, stunning the world by announcing his resignation Monday and leaving the already troubled Catholic Church to replace the leader of its 1 billion followers by Easter.

Not even his closest associates had advance word of the news, a bombshell that he dropped during a routine meeting of Vatican cardinals. And with no clear favorites to succeed him, another surprise likely awaits when the cardinals elect Benedict’s successor next month.

“Without doubt this is a historic moment,” said Cardinal Christoph Schoenborn, a protege and former theology student of Benedict’s who is considered a papal contender. “Right now, 1.2 billion Catholics the world over are holding their breath.”The Feb. 28 resignation allows for a fast-track conclave to elect a new pope, since the traditional nine days of mourning that would follow a pope’s death doesn’t have to be observed. It also gives the 85-year-old Benedict great sway over the choice of his successor. Though he will not himself 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.

Benedict said as recently as 2010 that a pontiff should resign if he got too old or infirm to do the job, but it was a tremendous surprise when he said in Latin that his “strength of mind and body” had diminished and that he couldn’t carry on. He said he would resign effective 8 p.m. local time on Feb. 28.

“All the cardinals remained shocked and were looking at each other,” said Monsignor Oscar Sanchez of Mexico, who was in the room at the time of the announcement.

As a top aide, Benedict watched from up close as Pope John Paul II suffered publicly from the Parkinson’s disease that enfeebled him in the final years of his papacy. Clearly Benedict wanted to avoid the same fate as his advancing age took its toll, though the Vatican insisted the announcement was not prompted by any specific malady.

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 and 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. Many of his stated priorities as pope also fell short: He failed to establish relations with China, heal the schism and reunite with the Orthodox Church, or reconcile with a group of breakaway, traditionalist Catholics.

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.

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.

The timing of Benedict’s announcement was significant: Lent begins this week on Ash Wednesday, the most solemn period on the church’s calendar that culminates with Holy Week and Easter on March 31.

It is also the period in which the world witnessed the final days of John Paul’s papacy in 2005.