The conclaves of cardinals which elect a new pope are laden with rituals and shrouded in secrecy, but tantalising details have emerged from previous votes of what really happens behind the sealed doors of the Sistine Chapel.
The 115 cardinals who have made their way to Rome are members of one of the most exclusive clubs in the world -- and once the doors close behind them on Tuesday with a cry of "Extra Omnes!" ("Everyone Out!") their deliberations must stay exclusive too.
Dressed in scarlet vestments and birettas (skullcaps), they must swear a solemn oath of secrecy or face ex-communication.
Even the cleaners and cooks who serve the cardinals must take a pledge to reveal nothing of what they overhear.
The cardinals' splendid isolation is all the more extraordinary in a world of camera phones, Twitter and Facebook -- no electronic devices can be taken in and the Sistine Chapel is swept for bugs.
Machiavellian maneuvering shroud papal conclave?
"The isolation is really complete. Television, radio and newspapers are inaccessible. Phones and mobiles are blocked. But we can talk," one cardinal said of the 2005 conclave which chose German-born Joseph Ratzinger as Benedict XVI.
The level of detail about the conclave that the cardinal revealed is rare, which is why he remains anonymous in the account published in Italian international foreign affairs review Limes.
He recalled that when he arrived at Casa Santa Marta, the spartan residence where the electors stay during their deliberations, he thought the blinds on the windows were broken because they failed to open. In fact, he soon discovered, they were sealed shut.
British cardinal Cormac Murphy-O'Connor, now the Archbishop Emeritus of Westminster, said that at the conclave eight years ago he was struck by the fact that the future leader of the world's 1.2 billion Catholics had to come from among the men locked in the room. Key locations for the papal election
"I remember looking around at all of the other 114 cardinals and thinking: 'One of us will be going out with a white cassock on," he told the BBC.
Unlike this time, there was a strong favourite from the start and the cardinals took just two days to elect Ratzinger and send up the puff of white smoke that signals a new pope has been found.
Know more: Timetable of papal conclave
"When the majority was reached... there was a gasp all around, and then everyone clapped," Murphy-O'Connor said.
Once Ratzinger had accepted his new role -- and chosen the name Benedict XVI -- he invited all of the cardinals to stay for a "convivial dinner", followed by the closest thing to a party that the elderly cardinals can have.
"In he comes, all dressed up. I often wondered what he felt, really. So anyway, we gave him a great clap, we had a very pleasant dinner with some champagne to drink a toast. Then we tried some songs," said Murphy-O'Connor, although it proved hard to settle on one that the polyglot gathering all knew.
While Benedict appeared happy to be elevated to pope, others have been extremely reluctant. In 1978, Cardinal Franz Koenig of Austria was part of the conclave which elected John Paul I. He recalled that after the new pope had gone onto the balcony to bless the crowd in St Peter's Square, "he said hardly anything, except to complain that we'd elected him".
Perhaps John Paul I felt what was coming -- he was found dead just 33 days later. The tension of that election in 1978 saw one nicotine-deprived cardinal -- some stories say it was an American, others say he was Spanish -- ask the new pope if he could have a cigarette.
John Paul I thought hard and long before replying: "Eminence, you may smoke, just as long as the smoke is white."
Will vested interests dissolve the sanctity of the conclave?
Although the Vatican insists that the cardinals participating in the upcoming conclave will vote their conscience, everybody knows, however, that power plays, vested interests and Machiavellian maneuvering are all part of the game, and that the horse-trading is already under way.
Can the fractious Italians rally behind a single candidate? Can the Americans live up to their surprise billing as a power broker? A look at last papal conclaves
And will all 115 cardinals from around the world be able to reach a meeting of minds on whether the church needs a people-friendly pope or a hard-edged manager able to tame Vatican bureaucrats?
This time there are no star cardinals and no big favorites, making the election wide open and allowing the possibility of a compromise candidate should there be deadlock.
One, dominated by the powerful Vatican bureaucracy called the Curia, is believed to be seeking a pope who will let it continue calling the shots as usual.
The one certainty about next pope? He'll wear Gammarelli
The speculation is that the Curia is pushing the candidacy of Brazilian Odilo Scherer, who has close ties to the Curia and would be expected to name an Italian insider as Secretary of State — the Vatican No. 2 who runs day-to-day affairs at the Holy See.
The frontrunners in the race
Narrowing down lists of about a dozen potential popes to a handful of serious hopefuls will definitely be one of the main tasks of the closed-door meetings that Catholic cardinals.
But as the rumours go, some of the expected top contenders to become the next head of the world's 1.2 billion Catholics, as cardinals gather in the Sistine Chapel are:
Angelo Scola -- The 71-year-old archbishop of Milan, an expert on bioethics, is a keen promoter of inter-religious dialogue, particularly between Muslims and Christians. His dense oratory could put off cardinals seeking a charismatic communicator.
Odilo Scherer -- The 63-year-old Brazilian is archbishop of Sao Paolo, home to five million faithful in a country that has the world's biggest Catholic population.
Looking for a new pope
On his archdiocesan website and in newspapers, Scherer regularly offers commentary on key issues. He is also very active on Twitter, boasting 20,000 followers of his account @DomOdiloScherer.
Marc Ouellet -- Canada's former archbishop of Quebec, 68, Ouellet now heads the influential Congregation of Bishops and is seen as the leading North American candidate for the papacy.
He could widen a rift between conservatives and reformists, according to Gilles Routhier, head of Laval University's theology faculty in Quebec City.
Peter Erdo -- Archbishop of Budapest since 2002 and a canon law expert who has taught at the Pontifical Lateran University in Rome, the 60-year-old Hungarian is known for his efforts to combat secularisation.
Christoph Schoenborn -- The archbishop of Vienna, 68, has called for a re-examination of the issue of priest celibacy in the wake of the child sex abuse scandal.
Know more about the top favorites for papacy
Jose Francisco Robles Ortega -- The 64-year-old archbishop of Guadalajara, has been described as reserved and lacking charisma and has taken a stand against the rampant violence linked to drug traffickers in his country, as well as rising secularism.
Luis Antonio Tagle -- The archbishop of Manila was last year appointed the Church's second youngest cardinal. The 55-year-old is tipped as an outsider to watch for his dynamism, charisma and stellar rise.
Timothy Dolan -- Archbishop of New York and a "modernist conservative", 63-year-old Dolan is media savvy -- a plus in today's social media society.
Sean O'malley -- The staunchly pro-life archbishop of Boston, 68, is a member of the Capuchin order who became the first cardinal with a blog in 2006.
Wilfrid Napier -- South African Cardinal Wilfrid Fox Napier is the 71-year-old archbishop of Durban who has said the Church is in a "profound crisis" and needs a new pope to implement "spiritual renewal".
The chances of an Indian pope are slim
The odds of an Indian cardinal being elected as the next pope may be slim, but they exist — about 100/1 to be precise. Bookmakers from around the world are offering odds on one of the five Indian cardinals of the 115 who will vote at the conclave that begins on Tuesday.
Can an Indian become the next pope? Bets are on
Odds are available through seven international bookmakers on Ivan Dias, former archbishop of Mumbai, even if they are heavily stacked against him.
Dias is on a list of about 90 candidates compiled by Oddschecker.com, which has aggregated odds from across bookmakers, including Paddy Power (125/1) and Ladbrookes (100/1). No other Indian cardinal features on the list.
Aside from Dias, cardinals from India who will be at the conclave are Telesphore Toppo (Archbishop of Patna), Oswald Gracias (Archbishop of Mumbai), George Alenchery and Baselios Cleemis, both from Kerala.
Read the goodbye tweets from cardinals
Last tweet before conclave: May Our Father hear and answer with love and mercy all prayers and sacrifices offered for fruitful outcome. God bless!" South African cardinal Wilfrid Napier told his thousands of followers. Cardinals will be completely isolated inside the Vatican walls for the duration of the conclave, which could last up to a few days. Jamming devices in the Sistine Chapel block all communications and the Vatican has said anyone caught tweeting will be excommunicated.
(With inputs from AP, AFP and Reuters)