Cardinals on Tuesday began a conclave under Michelangelo's famous frescoes in the Sistine Chapel to elect a successor to Benedict XVI, with the odds favouring another Western conservative as pope.
The 115 scarlet-robed cardinals filed into the chapel past liveried Swiss Guards, chanting the Latin hymn "Veni Creator Spiritus" ("Come Creator Spirit") to ask for divine guidance after Benedict's troubled eight-year papacy.
The "Princes of the Church" swore on the Bible never to reveal the secrets of their deliberations or face being cast out of the Church forever, before the doors of the chapel swung shut to indicate the beginning of the lock-in.
The chapel has been swept for bugs and installed with jamming devices to prevent electronic communications, with cardinals entirely cut off from the outside world behind the Vatican's walls until they have elected a new pontiff.
At an extravagant pre-conclave 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 reign over the world's 1.2 billion Catholics.
Several cardinals took to Twitter to say their goodbyes to their online flock before the conclave.
"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 — who were all appointed by Benedict XVI or his predecessor John Paul II — were set to hold a first round of voting later today after which the ballots will be burnt in a special stove in the Sistine Chapel.
The smoke is famously turned white if there is a new pope but the Vatican has already said it expects the smoke from the burning of ballots today to be black, indicating no pope has been elected.
From tomorrow, ballots will be burnt after two rounds of voting in the morning and two rounds in the afternoon — with the eyes of the world focused on the colour of the wisps of smoke emanating from a special chimney installed on the chapel's roof.
Among the candidates, three have emerged as favourites — Italy's Angelo Scola, Brazil's Odilo Scherer and Canada's Marc Ouellet.
Like "pope emeritus" Benedict XVI, all of them combine conservative views with social advocacy on issues like poverty, conflict and immigration.
But cardinals from Austria, Hungary, Mexico, the Philippines, South Africa and the United States — some of them with more reformist outlooks — were also rumoured to be in contention.