VATICAN CITY (AP) — With a few words in Latin, Pope Benedict XVI did yesterday what no pope has done in half a millennium, announcing his resignation and sending the already troubled Catholic Church scrambling to replace the leader of its one billion followers by Easter.

Not even his closest collaborators had advance word of the news, a bombshell that he dropped during a routine morning meeting of Vatican cardinals. And with no clear favourites 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 protegé 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 move 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 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 had 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 8:00 pm local time on February 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 modernising 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 half the world’s Catholics.

The Vatican stressed that no specific medical condition prompted Benedict’s decision, saying he remains fully lucid and took his decision independently.

“Any interference or intervention is alien to his style,” Lombardi said.

The pope has clearly slowed down significantly in recent years, cutting back his foreign travel and limiting his audiences. He now goes to and from the altar in St Peter’s Basilica on a moving platform to spare him the 100-yard walk down the aisle. Occasionally he uses a cane.

That Benedict is tired would be a perfectly normal diagnosis for an 85-year-old pope, even someone with no known serious health problems and a still-agile mind.

He has acknowledged having suffered a haemorrhagic stroke in 1991 that temporarily affected his vision, but he later made a full recovery. In 2009, the pope fell and suffered minor injuries when he broke one of his wrists while vacationing in the Alps.

A doctor familiar with the pope’s medical team told The Associated Press yesterday that the pontiff has no grave or life-threatening illnesses. But, the doctor said, the pope — like many men his age — has suffered some prostate problems. Beyond that, the pope is simply old and tired, the doctor said on condition of anonymity.

As early as 2010, Benedict began to look worn out: He had lost weight and didn’t seem fully engaged when visiting bishops briefed him on their dioceses. But as tired as he often seemed, he would also bounce back, enduring searing heat in Benin to caress a child and gamely hanging on when a freak storm forced him to cut short a speech during a youth festival in Madrid in 2011.

His 89-year-old brother, Georg Ratzinger, said doctors recently advised the pope not to take any more trans-Atlantic trips.

“His age is weighing on him,” Ratzinger told the dpa news agency in Germany. “At this age, my brother wants more rest.”

Benedict emphasised 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.

In a way, it shouldn’t have come as a surprise. Benedict himself in 2010 raised the possibility of resigning if he were too old or sick to continue.

“If a pope clearly realises that he is no longer physically, psychologically and spiritually capable of handling the duties of his office, then he has a right, and under some circumstances, also an obligation to resign,” Benedict said in the book Light of the World.

But he stressed that resignation was not an option to escape a particular burden, such as the sex abuse scandal.

“When the danger is great one must not run away. For that reason, now is certainly not the time to resign. Precisely at a time like this one must stand fast and endure the situation,” he said.

Although popes are allowed to resign, only a handful have 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.

There are good reasons why others haven’t followed suit, primarily because of the fear of a schism with two living popes. Lombardi sought to rule out such a scenario, saying church law makes clear that a resigning pope no longer has the right to govern the church.

When Benedict was elected in 2005 at age 78, he was the oldest pope chosen in nearly 300 years. At the time, he had already been planning to retire as the Vatican’s chief orthodoxy watchdog to spend his final years writing in the “peace and quiet” of his native Bavaria.

Yesterday, 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 south of Rome, and then live in the monastery.

All cardinals under age 80 are allowed to vote in the conclave, the secret meeting held in the Sistine Chapel where cardinals cast ballots to elect a new pope. As per tradition, the ballots are burned after each voting round; black smoke that snakes out of the chimney means no pope has been chosen, while white smoke means a pope has been elected.

There are currently 118 cardinals under age 80 and thus eligible to vote, 67 of whom were appointed by Benedict. However, four of them will turn 80 before the end of March. Depending on the date of the conclave, they may or may not be allowed to vote.

Benedict in 2007 passed a decree requiring a two-thirds majority to elect a pope, changing the rules established by John Paul in which the voting could shift to a simple majority after about 12 days of inconclusive balloting. Benedict did so to prevent cardinals from merely holding out until the 12 days had passed to push through a candidate who had only a slim majority.

Contenders to be his successor include Cardinal Angelo Scola, archbishop of Milan; Schoenborn, the archbishop of Vienna, and Cardinal Marc Ouellet, the Canadian head of the Vatican’s office for bishops.

Longshots include Cardinal Timothy Dolan of New York. Although Dolan is popular and backs the pope’s conservative line, being from a world superpower would probably hurt his chances. That might also rule out Cardinal Raymond Burke, an arch-conservative and the Vatican’s top judge, even though he is known and respected by most Vatican cardinals.

Monsignor Antonio Marto, the bishop of Fatima in central Portugal, said Benedict XVI’s resignation presents an opportunity to pick a church leader from a country outside Europe.