Surrounded by Michelangelo's imposing frescos imagining the beginning and the end of the world, cardinals locked themselves into the chapel following a final appeal for unity to heal the divisions that have been exposed by Pope Benedict XVI's shocking resignation and revelations of corruption and mismanagement in the Vatican bureaucracy.
Led by prelates holding a crucifix and candles, the 115 scarlet-robed prelates chanted the Litany of Saints, the hypnotic Gregorian chant imploring the intercession of the saints to guide their voting, before the master of liturgical ceremonies intoned "Extra omnes" or "all out" and closed the heavy wooden doors.
Outside, thousands of people braved cold night rain and packed St. Peter's Square, eyes fixed on the narrow chimney poking out of the Sistine Chapel roof. They were rewarded some three hours after the conclave began when thick black smoke billowed out of the chimney, signaling that no pope had been elected.
The cardinals now return to the Vatican hotel for the night and resume voting Wednesday morning.
Benedict XVI's surprise resignation has thrown the church into turmoil and exposed deep divisions among cardinals grappling with whether they need a manager to clean up the Vatican's dysfunctional bureaucracy or a pastor who can inspire Catholics at a time of waning faith and growing secularism.
The leading contenders for pope have fallen into one of the two camps, with Cardinal Angelo Scola, seen as favored by those hoping to shake up the powerful Vatican bureaucracy, and Brazilian Cardinal Odilo Scherer, favored by Vatican-based insiders who have defended the status quo. Other names included Canadian Cardinal Marc Ouellet, who heads the Vatican's powerful office for bishops, and U.S. Cardinal Timothy Dolan, the exuberant archbishop of New York.
In a final appeal before the conclave began, the dean of the College of Cardinals, retired Cardinal Angelo Sodano, urged unity within the church, asking the cardinal electors to put their differences aside for the good of the church and the future pope.
"Each of us is therefore called to cooperate with the Successor of Peter, the visible foundation of such an ecclesial unity," Sodano said. He said the job of pope is to be merciful, charitable and "tirelessly promote justice and peace."
He was interrupted by applause from the pews - not so much from the cardinals - when he referred to the "beloved and venerated" Benedict XVI and his "brilliant" pontificate.
Sitting in the front row was Benedict's longtime aide, Archbishop Georg Gaenswein, who reported that Benedict was watching the proceedings from the papal residence in Castel Gandolfo, according to a Vatican spokesman the Rev. Thomas Rosica.
For over a week, the cardinals have met behind closed doors to try to figure out who among them has the stuff to be pope and what his priorities should be. But they ended the debate on Monday with questions still unanswered, and many cardinals predicting a drawn-out election that will further expose the church's divisions. The conclave proceeds in silence, with no formal debate, behind closed doors.
During the discussions, Vatican-based cardinals defended their administration against complaints that they have been indifferent to the needs of cardinals in the field. At one point on Monday, the Brazilian head of one Vatican office reportedly drew applause for challenging the Vatican No. 2, who has been blamed for most of the bureaucracy's administrative failings.
"Let us pray for the cardinals who are to elect the Roman pontiff," read one of the prayers during the Mass. "May the Lord fill them with his Holy Spirit with understanding and good counsel, wisdom and discernment."
In his final radio address before being sequestered, Dolan on Tuesday said a certain calm had taken hold over him, as if "this gentle Roman rain is a sign of the grace of the Holy Spirit coming upon us."
He said he at least felt more settled about the task at hand. "And there's a sense of resignation and conformity with God's plan. It's magnificent," he said during his regular radio show on SiriusXM's Catholic Channel.
One of the pilgrims in the crowds Tuesday alluded to the challenges facing the church.
"It's a moment of crisis for the church, so we have to show support of the new pope," said Veronica Herrera, a real estate agent from Mexico who traveled to Rome for the conclave with her husband and daughter.
Yet the mood was not entirely somber.
A group of women who say they are priests launched pink smoke from a balcony overlooking the square to demand female ordination - a play on the famous smoke signals that will tell the world whether a pope has been elected. Two topless activists from Femen were dragged away from the edge of St. Peter's Square by police. Femen activists have previously protested the Vatican's opposition to gay marriage.
And in a bizarre twist, basketball star Dennis Rodman promised to be in St. Peter's Square on Wednesday in a makeshift popemobile as he campaigns for Cardinal Peter Turkson of Ghana to become the church's first black pope.
None of the cardinals will see it, since they will be sequestered inside the Vatican walls. They are allowed to travel only from the Vatican hotel through the gardens to the Sistine Chapel and back until they have elected a pope. No telephones, no newspapers, no television, no tweeting.
The focus of the ritual is on the Sistine Chapel, the Michelangelo masterwork painted over the course of nearly 30 years starting in 1508, so astonishing Pope John Paul II that he called it "the sanctuary of the theology of the body."
The most famous frescoes are "Creation" is a series of nine frescos running the length of the ceiling, the most well-known of which is the "Creation of Adam," showing God and Adam, their fingers reaching out to one another. "The Last Judgment" fresco behind the altar depicts a muscular Jesus surrounded by naked masses ascending to heaven and falling to hell.
Benedict, the former Cardinal Joseph Ratzinger, once wrote that the images of the beginning and the end of creation weighed on him when he was an elector in the 1978 conclave that brought John Paul to the papacy.
"I know well how we were exposed to those images in the hour of the important decisions, how they challenged us and how they instilled in our souls the greatness of our responsibility," Ratzinger said in 2003, at the presentation of a book of poetry by John Paul about the Sistine frescoes.
While few people expect a pontiff to be elected on the first ballot, the Vatican was ready: In the Room of Tears off the Sistine Chapel, three sizes of white cassocks hung from a clothes rack. Underneath, seven white shoe boxes were piled, presumably containing the various sizes of the red leather shoes that popes traditionally wear. The room gets its name from the weight of the job thrust upon the new pontiff.
The papal tailor Gammarelli delivered the clothes on Monday to ensure that the newly elected pope could change immediately into papal white as soon as he accepts the election. With the words "Habemus Papam" - or "We have a pope" - the pontiff then appears on the balcony of St. Peter's Basilica to greet the crowd.
But with so much uncertainty and upheaval going into the conclave, even the American cardinals couldn't agree on whether to expect a short or long conclave.
Cardinal Dolan this week publicly expressed optimism that the election would be wrapped up quickly. And on the eve of the conclave, he wrote a letter to New York priests, saying: "My guess is that we'd have a new Successor of St. Peter by Thursday evening," according to Dolan's spokesman, Joseph Zwilling.
That bullish stance stood in stark contrast with the view of Chicago Cardinal Francis George: His spokeswoman, Colleen Dolan, told The Associated Press that the cardinal suggested it could be a long affair. George raised the possibility that the cardinals may still be meeting by Saturday, when conclave rules require the cardinals to take a break and spend some time in prayer before resuming voting.
The faithful in St. Peter's square were also weighing in on the papal stakes.
"I don't think it's going to be a European pope," said Michael Flueckiger, a 38-year-old caretaker and sacristan of a church in Flamatt, Switzerland. "In Europe sometimes I think we have given away the gift of faith. Many people have lost the faith. They have lost their expectation in God."
Rachel Zoll, Karl Ritter and Daniela Petroff contributed.