It was the first of a series of highly
ritualistic ceremonies which will take place as 115 cardinals from
around the world gather in the Sistine Chapel beneath Michelangelo's
famous frescoed ceiling to choose a successor to Pope Benedict XVI, who
resigned last month.
The oath of
secrecy was taken by the Vatican's master of ceremonies, the doctors and
nurses who will assist elderly and infirm cardinals, members of the
Swiss Guard and the Vatican gendarmerie, staff from the Vatican 'hotel'
where the cardinals will stay and the drivers of mini-buses that will
take the less mobile cardinals to the Sistine Chapel.
The
conclave, a centuries-old tradition that mixes theatre, theology and
the utmost secrecy, will for a few days restore to Rome its ancient
title - "caput mundi" or capital of the world – as all eyes focus on the
chimney that has been installed on the roof of the chapel.
Black smoke means the cardinals have been unable to decide on a candidate, whereas white smoke signals that the election is over and the world's 1.2 billion Catholics have a new spiritual leader – the 265th successor to St Peter.
In their last meeting before the start of the conclave, the cardinals discussed the state of the Vatican bank, officially known as the Institute for Religious Works (IOR).
The bank has struggled to convince international authorities, including the Council of Europe's Moneyval committee on money laundering and terrorist financing, of its probity and transparency.
The cardinals were addressed by Tarcisio Bertone, who was the Vatican's de facto prime minister under Benedict XVI.
He heads a commission of cardinals that oversees the bank and outlined efforts to clean up its reputation.
The first day of the conclave begins with the cardinals in their scarlet vestments attending a special Mass known as Pro Eligendo Papa – For electing the Pope - in St Peter's Basilica.
In the afternoon they will process into the Sistine Chapel, led by a choir chanting the Litany of Saints, a Gregorian chant imploring the intercession of the saints to help guide voting.
One by one they will approach the altar beneath Michelangelo's Last Judgment, place their hands on a Bible and take an oath of secrecy in Latin by which they "promise and swear to observe with the greatest fidelity and with all persons, secrecy regarding everything that in any way relates to the election of the Roman Pontiff."
The chapel will have been swept for bugs and other recording devices and cardinals will be banned from using laptops or mobile phones – breaching the rules can result in excommunication.
A Vatican official, the master of liturgical ceremonies, will then deliver an order in Latin – "Extra omnes!" (Everybody out!) telling anybody who is not directly involved in the election to leave immediately.
The cardinals will be seated on chairs made of cherry wood behind 12 wooden tables covered in satin and cloth.
There will be a 13th table positioned in front of the altar, on which will be placed a silver urn into which the cardinals will cast their secret ballot papers.
Each cardinal writes his choice on a ballot paper inscribed with the words "Eligo in summum pontificem," or "I elect as Supreme Pontiff."
The folded ballot is placed on a shallow metal "paten" plate, used to hold communion wafers during Mass, and then slid into a large silver urn.
The votes will then be burned in a special stove that has been installed in one corner of the Sistine Chapel, with the first wisps of smoke expected at around 8pm Italy time (7pm UK).
Under Vatican constitutional law, cardinals must come to a two-thirds majority agreement, and voting is expected to continue at least until Wednesday.
Once the majority has been achieved, the most senior cardinal from the order of deacons will ask the chosen cardinal if he is prepared to become Pope.
If the answer in Latin is "Accepto" (I Accept), he is taken into a side room known as the Stanza delle Lacrime, or Room of Tears, where he is given help to take off his scarlet cassock and change into the white vestments of the papacy.
He also has to decide by what name he wishes to be called – the name-changing tradition dates back to the sixth century when a priest named Mercury who was elected Pope felt his name was too pagan and changed it to John II.
The senior cardinal, in this case a Frenchman, Jean-Louis Tauran, will then step out onto the balcony of St Peter's and announce in Latin: "Annuntio vobis gaudium magnum. Habemus papam! (I announce to you a great joy. We have a pope!)".
He will announce the name of the elected cardinal and the papal title he has chosen.
The new Pope then gives his first blessing, watched by huge crowds in St Peter's Square and on television by millions of people around the world.
This will be the 25th conclave held in the Sistine Chapel – in the past, some conclaves were held in Rome's Quirinale Palace, in other cities such as Venice or even outside Italy, in Avignon and Lyons.
The word derives from the Latin "cum clavi", with a key, because cardinals used to be shut behind locked doors until they came to a decision.
In past centuries cardinals argued for months, even years, but the longest conclave of the 20th century lasted five days – when Pius XI was elected in 1922.