Cardinals prepared on Tuesday for the start of an historic conclave to elect a new pope after Benedict XVI's shock resignation, with the odds favouring a Western conservative to lead the Catholic world.
At a grandiose mass in St Peter's Basilica the cardinals prayed for unity in the Church -- a stark reminder of the infighting that often overshadowed Benedict's eight-year pontificate.
The 115 scarlet-robed cardinals burst into thunderous applause when the dean of the College of Cardinals, Angelo Sodano, publicly thanked the "beloved and venerable" Benedict in his homily.
As the cardinals prepared for the conclave, rainstorms drenched thousands of pilgrims watching the momentous event on four giant screens in St Peter's Square.
One barefoot man in a sackcloth habit knelt on the cobblestones in the pouring rain and was joined by another pilgrim who bowed his head in prayer, as a hymn echoed across the square.
The "Princes of the Church" will be cut off from the outside world inside the Vatican walls until they have made their choice in a centuries-old ritual -- much of it carried out in Latin.
They took to Twitter to say their goodbyes to their online flock before the conclave, where jamming devices will block any communications.
"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 said.
The cardinals have to swear not to reveal anything about their talks on pain of excommunication.
They will enter the Sistine Chapel in a procession under Michelangelo's famous frescoes starting at 1530 GMT, chanting to invoke divine guidance.
The cardinals are then set to hold a first round of voting after which the ballots will be burnt in a special stove in the chapel.
The smoke famously turns white if there is a new pope but the Vatican has already said it expects the smoke from the burning of Tuesday's ballots to be black, indicating no pope has been elected.
From Wednesday, ballots will be burnt after two rounds of voting in the morning and two rounds in the afternoon.
Conclaves normally last no more than a few days. A two-thirds majority is required for a winner, a rule that led the first-ever conclave in the 13th century to drag on for nearly three years.
The longest conclave in the past century -- in 1922 -- lasted only five days. Benedict's election after John Paul II's death in 2005 took just two days.
Trio of frontrunners
Among the candidates, three have emerged as favourites -- Italy's Angelo Scola, Brazil's Odilo Scherer and Canada's Marc Ouellet -- all of them conservatives like "pope emeritus" Benedict XVI.
But there are more names in the rumour mill including cardinals from Austria, Hungary, Mexico, the Philippines, South Africa and the United States.
Bookmakers said Scola was the favourite, followed by Ghana's Peter Turkson and Scherer.
Irish bookmaker Paddy Power and Britain's William Hill said Scola's chances had improved dramatically and both gave the Milan archbishop odds of 9/4 to be the next pope.
But Mexican cardinal Norberto Rivera Carrera told Italian daily La Stampa that there was no agreement yet among the cardinals.
"Some imagine him to be more academic, able to establish a dialogue with culture. Others ask for someone who is close to the people. Others still want someone with more authority to put some Church problems in order," he said.
"So far, there is no majority."
A few key aims unite many of the cardinals, like reforming the intrigue-ridden Vatican bureaucracy, countering rising secularism in the West and re-igniting Catholic faith in the way the charismatic John Paul II did.
The scandal over decades of sexual abuse of children by paedophile priests -- and the efforts made by senior prelates to cover up the crimes -- has cast a
long shadow over the Church.
British cardinal Keith O'Brien was forced to recuse himself from the conclave just days ago after claims surfaced of sexual misconduct with priests and seminarians in the 1980s.
There have been calls too from within the Church for a rethink of some basic tenets such as priestly celibacy, the uniform ban on artificial contraception and even allowing women to be priests as in other Christian denominations.
A series of pre-conclave meetings last week offered a rare chance to air grievances, and Italian media on Tuesday reported a clash between two senior cardinals over what to do about the Vatican's scandal-tainted bank.
The tradition of holding conclaves goes back to the 13th century when cardinals were locked into the papal palace in Viterbo near Rome by an angry crowd because they were taking too long to choose a pope.
The 85-year-old Benedict announced on February 11 that he no longer had the strength of body and mind to keep up with the modern world.
In a series of emotional farewells, the German said he would live "hidden from the world" and wanted only to be "a simple pilgrim".