Now all eyes will turn to the chimney installed on the roof of the historic chapel.
From this point on, the only clue the world will have of what is happening inside will be periodic puffs of smoke that follow each round of voting.
Black smoke, no pope. White smoke, success.
On a day rich with symbolism, the scarlet-clad cardinals entered the Sistine Chapel in solemn procession, chanting prayers and watched over by the magnificent paintings of Renaissance artist Michelangelo.
Each of the cardinal-electors — those under age 80 who are eligible to vote — then swore an oath of secrecy, led by Cardinal Giovanni Battista Re, the most senior cardinal in the conclave.
A designated official then gave the order in Latin, “Extra omnes” — that is, “Those who are extra, leave.”
With all those not taking part in the conclave gone, the cardinals will remain locked in total isolation until one candidate can garner two-thirds of their votes.
That man will emerge from the process as the new spiritual leader of the world’s 1.2 billion Roman Catholics.
The cardinals will probably vote Tuesday, but they don’t have to, Vatican spokesman the Rev. Federico Lombardi said Monday.
If they do, it’s likely the first smoke might be seen around 8 p.m. (3 p.m. ET), he said.
Huddled under umbrellas as the rain came down, crowds of curious onlookers watched on big screens set up in St. Peter’s Square until the doors to the Sistine Chapel were shut.
Earlier, the cardinals celebrated a special morning Mass at St. Peter’s Basilica, where they prayed for guidance in making a choice that could be crucial to the future direction of a church rocked by scandal in recent years.
Applause echoed around St. Peter’s as Cardinal Angelo Sodano, dean of the College of Cardinals, offered thanks for the “brilliant pontificate” of Benedict XVI, whose unexpected resignation precipitated the selection of a new pope.
Sodano’s homily focused on a message of love and unity, calling on all to cooperate with the new pontiff in the service of the church.
“My brothers, let us pray that the Lord will grant us a pontiff who will embrace this noble mission with a generous heart,” he concluded.
Members of the public had waited in long lines Tuesday morning to join the Mass, which was open to all. As the service began, the morning’s brilliant sunshine came to an abrupt end, with the skies letting loose thunder, lightning and a torrential downpour.
Before the service, the cardinal-electors moved into Casa Santa Marta, their residence at the Vatican for the duration of the conclave.
Jamming devices have been put in place to stop them from communicating with the outside world using mobile phones or other electronic means as they make their decision.
Rome is abuzz
Rome was abuzz Monday with preparations for the conclave, from the 5,600 journalists the Vatican said had been accredited to cover the event to the red curtains unfurled from the central balcony at St. Peter’s, the spot where the world will meet the new pope once he is elected.
Tailors have also completed sets of clothes for the new pope to wear as soon as he is elected, in three different sizes.
Video released by the Vatican over the weekend showed the installation of a pair of stoves inside the chapel. One is used to burn the cardinals’ ballots after they are cast and the other to send up the smoke signal — the one that alerts the world that a vote has been taken and whether there’s a new pope.
Workers scaled the roof of the chapel Saturday to install the chimneys.
When cardinals elected Benedict in 2005, the white smoke signaling the decision came about six hours after an earlier, inconclusive vote, Lombardi said.
It took another 50 minutes for Benedict to dress, pray and finally appear on the balcony of St. Peter’s, he said.
The longest conclave held since the turn of the 20th century lasted five days.
On Monday, cardinals held the last of several days of meetings, known as General Congregations, to discuss church affairs and get acquainted. Lombardi said 152 cardinals were on hand for the final meeting.
As well as getting to know their counterparts from around the world, the cardinals discussed the major issues facing the church, including its handling of allegations of child sex abuse by priests and a scandal over leaks from the Vatican last year that revealed claims of corruption, as well as the church’s future direction.
Church rules prevent cardinals over the age of 80 from participating in the conclave but allow them to attend the meetings that precede the vote.
Who will be chosen?
Meanwhile, the Italian press is full of speculation about which cardinal may win enough support from his counterparts to be elected, and what regional alliances are being formed.
According to CNN Vatican analyst John Allen, also a correspondent for the National Catholic Reporter, the race is wide open as the cardinals enter the conclave.
Unlike in 2005, when Benedict XVI was believed to be the favorite going into the secret election, no one has emerged as a clear frontrunner this time around, he said.
Some names have cropped up in media reports as possible contenders, however. They include Italy’s Cardinal Angelo Scola; Brazil’s Odilo Scherer; Marc Ouellet of Quebec, Canada; U.S. cardinals Sean O’Malley of Boston and Timothy Dolan of New York; and Ghana’s Peter Turkson.
More than 80% of Africans believe their continent is ready for an African pope, but only 61% believe the world is, an exclusive survey for CNN has found.
A mobile phone survey of 20,000 Africans from 11 nations, conducted by CNN in conjunction with crowd sourcing company Jana, also found that 86% thought an African pope would increase support for Catholicism in Africa.
Italy potentially wields the most power within the conclave, with 28 of the 115 votes, making it the largest bloc in the College of Cardinals. The United States is second with 11. Altogether, 48 countries are represented among the cardinal-electors.
“Many would say it’s all about politics at this point,” Monsignor Rick Hilgartner, head of U.S. Conference of Catholic Bishops Secretariat on Divine Worship, told CNN, “but I think it’s important to remember that they also recognize that this is a very spiritual moment.”
Once the doors close and the conclave begins, he says, it’s less about politicking and “more about prayer as they each in silence write their votes.”
Sixty-seven of the cardinal-electors were appointed by Benedict, who stepped down at the end of last month, becoming the first pontiff to do so in six centuries.
CNN’s Dan Rivers and Richard Allen Greene reported from Rome, and Laura Smith-Spark wrote and reported in London. CNN’s Hada Messia, Ed Payne and Michael Pearson and journalist Livia Borghese also contributed to this report.