Vatican City, March 12 - Cardinals will gather in the Sistine Chapel later on Tuesday, when the conclave to elect the new pope begins. Early on Tuesday cardinals attended the pre-conclave 'pro eligendo' mass in St Peter's Basilica. That mass was open to all of the Catholic Church's cardinals, most of whom have been in Rome for over a week for the "general congregations" to prepare for the election of Benedict XVI's successor. At around 16:30 Italian time the 115 of them who are eligible to vote as they are under 80 will enter the chapel that hosts Michelangelo's famous frescoed ceiling and his depiction of the Last Judgment and the conclave will begin. During the conclave the cardinal electors are sworn to total secrecy and they will be shut off from all contact with the outside world, spending their time between the Sistine Chapel and Vatican's Santa Martha hotel. The cardinals are expected to hold their first vote late on Tuesday afternoon. This is likely to be inconclusive and Vatican spokesman Father Federico Lombardy said the cardinals may not hold a vote at all on Tuesday. They hold four ballots a day from Wednesday. To be elected pope, a cardinal needs a two-thirds majority in the conclave - or 77 votes. Black smoke from the chimney on the roof of the Sistine Chapel indicates a vote has been inconclusive, while white smoke and the ringing of St. Peter's bells will announce a new pope has been elected. Benedict, 85, stepped down at the end of last month after announcing that he no longer had the mental and physical strength to lead the world's 1.2 billion Catholics.